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Human activity affects global surface temperatures by changing Earth ’s radiative balance—the “give and take” between what comes in during the day and what Earth emits at night. Increases in greenhouse gases —i.e., trace gases such as carbon dioxide and methane that absorb heat energy emitted from Earth’s surface and reradiate it back—generated by industry and transportation cause the atmosphere to retain more heat, which increases temperatures and alters precipitation patterns.

Global warming, the phenomenon of increasing average air temperatures near Earth’s surface over the past one to two centuries, happens mostly in the troposphere , the lowest level of the atmosphere, which extends from Earth’s surface up to a height of 6–11 miles. This layer contains most of Earth’s clouds and is where living things and their habitats and weather primarily occur.

Continued global warming is expected to impact everything from energy use to water availability to crop productivity throughout the world. Poor countries and communities with limited abilities to adapt to these changes are expected to suffer disproportionately. Global warming is already being associated with increases in the incidence of severe and extreme weather, heavy flooding , and wildfires —phenomena that threaten homes, dams, transportation networks, and other facets of human infrastructure. Learn more about how the IPCC’s Sixth Assessment Report, released in 2021, describes the social impacts of global warming.

Polar bears live in the Arctic , where they use the region’s ice floes as they hunt seals and other marine mammals . Temperature increases related to global warming have been the most pronounced at the poles, where they often make the difference between frozen and melted ice. Polar bears rely on small gaps in the ice to hunt their prey. As these gaps widen because of continued melting, prey capture has become more challenging for these animals.

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global warming , the phenomenon of increasing average air temperatures near the surface of Earth over the past one to two centuries. Climate scientists have since the mid-20th century gathered detailed observations of various weather phenomena (such as temperatures, precipitation , and storms) and of related influences on climate (such as ocean currents and the atmosphere’s chemical composition). These data indicate that Earth’s climate has changed over almost every conceivable timescale since the beginning of geologic time and that human activities since at least the beginning of the Industrial Revolution have a growing influence over the pace and extent of present-day climate change .

Giving voice to a growing conviction of most of the scientific community , the Intergovernmental Panel on Climate Change (IPCC) was formed in 1988 by the World Meteorological Organization (WMO) and the United Nations Environment Program (UNEP). The IPCC’s Sixth Assessment Report (AR6), published in 2021, noted that the best estimate of the increase in global average surface temperature between 1850 and 2019 was 1.07 °C (1.9 °F). An IPCC special report produced in 2018 noted that human beings and their activities have been responsible for a worldwide average temperature increase between 0.8 and 1.2 °C (1.4 and 2.2 °F) since preindustrial times, and most of the warming over the second half of the 20th century could be attributed to human activities.

AR6 produced a series of global climate predictions based on modeling five greenhouse gas emission scenarios that accounted for future emissions, mitigation (severity reduction) measures, and uncertainties in the model projections. Some of the main uncertainties include the precise role of feedback processes and the impacts of industrial pollutants known as aerosols , which may offset some warming. The lowest-emissions scenario, which assumed steep cuts in greenhouse gas emissions beginning in 2015, predicted that the global mean surface temperature would increase between 1.0 and 1.8 °C (1.8 and 3.2 °F) by 2100 relative to the 1850–1900 average. This range stood in stark contrast to the highest-emissions scenario, which predicted that the mean surface temperature would rise between 3.3 and 5.7 °C (5.9 and 10.2 °F) by 2100 based on the assumption that greenhouse gas emissions would continue to increase throughout the 21st century. The intermediate-emissions scenario, which assumed that emissions would stabilize by 2050 before declining gradually, projected an increase of between 2.1 and 3.5 °C (3.8 and 6.3 °F) by 2100.

Many climate scientists agree that significant societal, economic, and ecological damage would result if the global average temperature rose by more than 2 °C (3.6 °F) in such a short time. Such damage would include increased extinction of many plant and animal species, shifts in patterns of agriculture , and rising sea levels. By 2015 all but a few national governments had begun the process of instituting carbon reduction plans as part of the Paris Agreement , a treaty designed to help countries keep global warming to 1.5 °C (2.7 °F) above preindustrial levels in order to avoid the worst of the predicted effects. Whereas authors of the 2018 special report noted that should carbon emissions continue at their present rate, the increase in average near-surface air temperature would reach 1.5 °C sometime between 2030 and 2052, authors of the AR6 report suggested that this threshold would be reached by 2041 at the latest.

The AR6 report also noted that the global average sea level had risen by some 20 cm (7.9 inches) between 1901 and 2018 and that sea level rose faster in the second half of the 20th century than in the first half. It also predicted, again depending on a wide range of scenarios, that the global average sea level would rise by different amounts by 2100 relative to the 1995–2014 average. Under the report’s lowest-emission scenario, sea level would rise by 28–55 cm (11–21.7 inches), whereas, under the intermediate emissions scenario, sea level would rise by 44–76 cm (17.3–29.9 inches). The highest-emissions scenario suggested that sea level would rise by 63–101 cm (24.8–39.8 inches) by 2100.

The scenarios referred to above depend mainly on future concentrations of certain trace gases, called greenhouse gases , that have been injected into the lower atmosphere in increasing amounts through the burning of fossil fuels for industry, transportation , and residential uses. Modern global warming is the result of an increase in magnitude of the so-called greenhouse effect , a warming of Earth’s surface and lower atmosphere caused by the presence of water vapour , carbon dioxide , methane , nitrous oxides , and other greenhouse gases. In 2014 the IPCC first reported that concentrations of carbon dioxide, methane, and nitrous oxides in the atmosphere surpassed those found in ice cores dating back 800,000 years.

Of all these gases, carbon dioxide is the most important, both for its role in the greenhouse effect and for its role in the human economy. It has been estimated that, at the beginning of the industrial age in the mid-18th century, carbon dioxide concentrations in the atmosphere were roughly 280 parts per million (ppm). By the end of 2022 they had risen to 419 ppm, and, if fossil fuels continue to be burned at current rates, they are projected to reach 550 ppm by the mid-21st century—essentially, a doubling of carbon dioxide concentrations in 300 years.

A vigorous debate is in progress over the extent and seriousness of rising surface temperatures, the effects of past and future warming on human life, and the need for action to reduce future warming and deal with its consequences. This article provides an overview of the scientific background related to the subject of global warming. It considers the causes of rising near-surface air temperatures, the influencing factors, the process of climate research and forecasting, and the possible ecological and social impacts of rising temperatures. For an overview of the public policy developments related to global warming occurring since the mid-20th century, see global warming policy . For a detailed description of Earth’s climate, its processes, and the responses of living things to its changing nature, see climate . For additional background on how Earth’s climate has changed throughout geologic time , see climatic variation and change . For a full description of Earth’s gaseous envelope, within which climate change and global warming occur, see atmosphere .

Causes of global warming, explained

Human activity is driving climate change, including global temperature rise.

The average temperature of the Earth is rising at nearly twice the rate it was 50 years ago. This rapid warming trend cannot be explained by natural cycles alone, scientists have concluded. The only way to explain the pattern is to include the effect of greenhouse gases (GHGs) emitted by humans.

Current levels of the greenhouse gases carbon dioxide, methane, and nitrous oxide in our atmosphere are higher than at any point over the past 800,000 years , and their ability to trap heat is changing our climate in multiple ways .

IPCC conclusions

To come to a scientific conclusion on climate change and what to do about it, the United Nations in 1988 formed a group called the Intergovernmental Panel on Climate Change , or IPCC. The IPCC meets every few years to review the latest scientific findings and write a report summarizing all that is known about global warming. Each report represents a consensus, or agreement, among hundreds of leading scientists.

One of the first things the IPCC concluded is that there are several greenhouse gases responsible for warming, and humans emit them in a variety of ways. Most come from the combustion of fossil fuels in cars, buildings, factories, and power plants. The gas responsible for the most warming is carbon dioxide, or CO2. Other contributors include methane released from landfills, natural gas and petroleum industries, and agriculture (especially from the digestive systems of grazing animals); nitrous oxide from fertilizers; gases used for refrigeration and industrial processes; and the loss of forests that would otherwise store CO2.

Gaseous abilities

Different greenhouse gases have very different heat-trapping abilities. Some of them can trap more heat than an equivalent amount of CO2. A molecule of methane doesn't hang around the atmosphere as long as a molecule of carbon dioxide will, but it is at least 84 times more potent over two decades. Nitrous oxide is 264 times more powerful than CO2.

Other gases, such as chlorofluorocarbons, or CFCs—which have been banned in much of the world because they also degrade the ozone layer—have heat-trapping potential thousands of times greater than CO2. But because their emissions are much lower than CO2 , none of these gases trap as much heat in the atmosphere as CO2 does.

When those gases that humans are adding to Earth's atmosphere trap heat, it’s called the "greenhouse effect." The gases let light through but then keep much of the heat that radiates from the surface from escaping back into space, like the glass walls of a greenhouse. The more greenhouse gases in the atmosphere, the more dramatic the effect, and the more warming that happens.

Climate change continues

Despite global efforts to address climate change, including the landmark 2015 Paris climate agreement , carbon dioxide emissions from fossil fuels continue to rise, hitting record levels in 2018 .

Many people think of global warming and climate change as synonyms, but scientists prefer to use “climate change” when describing the complex shifts now affecting our planet’s weather and climate systems. Climate change encompasses not only rising average temperatures but also extreme weather events, shifting wildlife populations and and habitats, rising seas , and a range of other impacts.

Read next: Global Warming Effects

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ENCYCLOPEDIC ENTRY

Global warming.

The causes, effects, and complexities of global warming are important to understand so that we can fight for the health of our planet.

Earth Science, Climatology

Tennessee Power Plant

Ash spews from a coal-fueled power plant in New Johnsonville, Tennessee, United States.

Photograph by Emory Kristof/ National Geographic

Global warming is the long-term warming of the planet’s overall temperature. Though this warming trend has been going on for a long time, its pace has significantly increased in the last hundred years due to the burning of fossil fuels . As the human population has increased, so has the volume of fossil fuels burned. Fossil fuels include coal, oil, and natural gas, and burning them causes what is known as the “greenhouse effect” in Earth’s atmosphere.

The greenhouse effect is when the sun’s rays penetrate the atmosphere, but when that heat is reflected off the surface cannot escape back into space. Gases produced by the burning of fossil fuels prevent the heat from leaving the atmosphere. These greenhouse gasses are carbon dioxide , chlorofluorocarbons, water vapor , methane , and nitrous oxide . The excess heat in the atmosphere has caused the average global temperature to rise overtime, otherwise known as global warming.

Global warming has presented another issue called climate change. Sometimes these phrases are used interchangeably, however, they are different. Climate change refers to changes in weather patterns and growing seasons around the world. It also refers to sea level rise caused by the expansion of warmer seas and melting ice sheets and glaciers . Global warming causes climate change, which poses a serious threat to life on Earth in the forms of widespread flooding and extreme weather. Scientists continue to study global warming and its impact on Earth.

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The Basics of Climate Change

Greenhouse gases affect Earth’s energy balance and climate

The Sun serves as the primary energy source for Earth’s climate. Some of the incoming sunlight is reflected directly back into space, especially by bright surfaces such as ice and clouds, and the rest is absorbed by the surface and the atmosphere. Much of this absorbed solar energy is re-emitted as heat (longwave or infrared radiation). The atmosphere in turn absorbs and re-radiates heat, some of which escapes to space. Any disturbance to this balance of incoming and outgoing energy will affect the climate. For example, small changes in the output of energy from the Sun will affect this balance directly.

If all heat energy emitted from the surface passed through the atmosphere directly into space, Earth’s average surface temperature would be tens of degrees colder than today. Greenhouse gases in the atmosphere, including water vapour, carbon dioxide, methane, and nitrous oxide, act to make the surface much warmer than this because they absorb and emit heat energy in all directions (including downwards), keeping Earth’s surface and lower atmosphere warm [Figure B1]. Without this greenhouse effect, life as we know it could not have evolved on our planet. Adding more greenhouse gases to the atmosphere makes it even more effective at preventing heat from escaping into space. When the energy leaving is less than the energy entering, Earth warms until a new balance is established.

Greenhouse gases emitted by human activities alter Earth’s energy balance and thus its climate. Humans also affect climate by changing the nature of the land surfaces (for example by clearing forests for farming) and through the emission of pollutants that affect the amount and type of particles in the atmosphere.

Scientists have determined that, when all human and natural factors are considered, Earth’s climate balance has been altered towards warming, with the biggest contributor being increases in CO 2 .

Figure b1. Greenhouse gases in the atmosphere, including water vapour, carbon dioxide, methane, and nitrous oxide, absorb heat energy and emit it in all directions (including downwards), keeping Earth’s surface and lower atmosphere warm. Adding more greenhouse gases to the atmosphere enhances the effect, making Earth’s surface and lower atmosphere even warmer. Image based on a figure from US EPA.

Human activities have added greenhouse gases to the atmosphere

The atmospheric concentrations of carbon dioxide, methane, and nitrous oxide have increased significantly since the Industrial Revolution began. In the case of carbon dioxide, the average concentration measured at the Mauna Loa Observatory in Hawaii has risen from 316 parts per million (ppm) in 1959 (the first full year of data available) to more than 411 ppm in 2019 [Figure B2]. The same rates of increase have since been recorded at numerous other stations worldwide. Since preindustrial times, the atmospheric concentration of CO 2  has increased by over 40%, methane has increased by more than 150%, and nitrous oxide has increased by roughly 20%. More than half of the increase in CO 2  has occurred since 1970. Increases in all three gases contribute to warming of Earth, with the increase in CO 2  playing the largest role. See page B3 to learn about the sources of human emitted greenhouse gases.  Learn about the sources of human emitted greenhouse gases.

Scientists have examined greenhouse gases in the context of the past. Analysis of air trapped inside ice that has been accumulating over time in Antarctica shows that the CO 2  concentration began to increase significantly in the 19th century [Figure B3], after staying in the range of 260 to 280 ppm for the previous 10,000 years. Ice core records extending back 800,000 years show that during that time, CO 2  concentrations remained within the range of 170 to 300 ppm throughout many “ice age” cycles -  learn about the ice ages  -  and no concentration above 300 ppm is seen in ice core records until the past 200 years.

Measurements of the forms (isotopes) of carbon in the modern atmosphere show a clear fingerprint of the addition of “old” carbon (depleted in natural radioactive  14 C) coming from the combustion of fossil fuels (as opposed to “newer” carbon coming from living systems). In addition, it is known that human activities (excluding land use changes) currently emit an estimated 10 billion tonnes of carbon each year, mostly by burning fossil fuels, which is more than enough to explain the observed increase in concentration. These and other lines of evidence point conclusively to the fact that the elevated CO 2  concentration in our atmosphere is the result of human activities. 

Fig b2. Measurements of atmospheric CO 2  since 1958 from the Mauna Loa Observatory in Hawaii (black) and from the South Pole (red) show a steady annual increase in atmospheric CO 2  concentration. The measurements are made at remote places like these because they are not greatly influenced by local processes, so therefore they are representative of the background atmosphere. The small up-and-down saw-tooth pattern reflects seasonal changes in the release and uptake of CO 2  by plants. Source: Scripps CO2 Program

Figure b3. CO 2  variations during the past 1,000 years, obtained from analysis of air trapped in an ice core extracted from Antarctica (red squares), show a sharp rise in atmospheric CO 2  starting in the late 19th century. Modern atmospheric measurements from Mauna Loa are superimposed in gray. Source: figure by Eric Wolff, data from Etheridge et al., 1996; MacFarling Meure et al., 2006; Scripps CO 2  Program. 

Climate records show a warming trend

Estimating global average surface air temperature increase requires careful analysis of millions of measurements from around the world, including from land stations, ships, and satellites. Despite the many complications of synthesising such data, multiple independent teams have concluded separately and unanimously that global average surface air temperature has risen by about 1 °C (1.8 °F) since 1900 [Figure B4]. Although the record shows several pauses and accelerations in the increasing trend, each of the last four decades has been warmer than any other decade in the instrumental record since 1850.

Going further back in time before accurate thermometers were widely available, temperatures can be reconstructed using climate-sensitive indicators “proxies” in materials such as tree rings, ice cores, and marine sediments. Comparisons of the thermometer record with these proxy measurements suggest that the time since the early 1980s has been the warmest 40-year period in at least eight centuries, and that global temperature is rising towards peak temperatures last seen 5,000 to 10,000 years ago in the warmest part of our current interglacial period.

Many other impacts associated with the warming trend have become evident in recent years. Arctic summer sea ice cover has shrunk dramatically. The heat content of the ocean has increased. Global average sea level has risen by approximately 16 cm (6 inches) since 1901, due both to the expansion of warmer ocean water and to the addition of melt waters from glaciers and ice sheets on land. Warming and precipitation changes are altering the geographical ranges of many plant and animal species and the timing of their life cycles. In addition to the effects on climate, some of the excess CO 2  in the atmosphere is being taken up by the ocean, changing its chemical composition (causing ocean acidification).

Figure b4. Earth’s global average surface temperature has risen, as shown in this plot of combined land and ocean measurements from 1850 to 2019 derived from three independent analyses of the available data sets. The top panel shows annual average values from the three analyses, and the bottom panel shows decadal average values, including the uncertainty range (grey bars) for the maroon (HadCRUT4) dataset. The temperature changes are relative to the global average surface temperature, averaged from 1961−1990. Source: Based on IPCC AR5, data from the HadCRUT4 dataset (black), NOAA Climate.gov; data from UK Met Office Hadley Centre (maroon), US National Aeronautics and Space Administration Goddard Institute for Space Studies (red), and US National Oceanic and Atmospheric Administration National Centers for Environmental Information (orange). 

Many complex processes shape our climate

Based just on the physics of the amount of energy that CO 2 absorbs and emits, a doubling of atmospheric CO 2 concentration from pre-industrial levels (up to about 560 ppm) would by itself cause a global average temperature increase of about 1 °C (1.8 °F). In the overall climate system, however, things are more complex; warming leads to further effects (feedbacks) that either amplify or diminish the initial warming.

The most important feedbacks involve various forms of water. A warmer atmosphere generally contains more water vapour. Water vapour is a potent greenhouse gas, thus causing more warming; its short lifetime in the atmosphere keeps its increase largely in step with warming. Thus, water vapour is treated as an amplifier, and not a driver, of climate change. Higher temperatures in the polar regions melt sea ice and reduce seasonal snow cover, exposing a darker ocean and land surface that can absorb more heat, causing further warming. Another important but uncertain feedback concerns changes in clouds. Warming and increases in water vapour together may cause cloud cover to increase or decrease which can either amplify or dampen temperature change depending on the changes in the horizontal extent, altitude, and properties of clouds. The latest assessment of the science indicates that the overall net global effect of cloud changes is likely to be to amplify warming.

The ocean moderates climate change. The ocean is a huge heat reservoir, but it is difficult to heat its full depth because warm water tends to stay near the surface. The rate at which heat is transferred to the deep ocean is therefore slow; it varies from year to year and from decade to decade, and it helps to determine the pace of warming at the surface. Observations of the sub-surface ocean are limited prior to about 1970, but since then, warming of the upper 700 m (2,300 feet) is readily apparent, and deeper warming is also clearly observed since about 1990.

Surface temperatures and rainfall in most regions vary greatly from the global average because of geographical location, in particular latitude and continental position. Both the average values of temperature, rainfall, and their extremes (which generally have the largest impacts on natural systems and human infrastructure), are also strongly affected by local patterns of winds.

Estimating the effects of feedback processes, the pace of the warming, and regional climate change requires the use of mathematical models of the atmosphere, ocean, land, and ice (the cryosphere) built upon established laws of physics and the latest understanding of the physical, chemical and biological processes affecting climate, and run on powerful computers. Models vary in their projections of how much additional warming to expect (depending on the type of model and on assumptions used in simulating certain climate processes, particularly cloud formation and ocean mixing), but all such models agree that the overall net effect of feedbacks is to amplify warming.

Human activities are changing the climate

Rigorous analysis of all data and lines of evidence shows that most of the observed global warming over the past 50 years or so cannot be explained by natural causes and instead requires a significant role for the influence of human activities.

In order to discern the human influence on climate, scientists must consider many natural variations that affect temperature, precipitation, and other aspects of climate from local to global scale, on timescales from days to decades and longer. One natural variation is the El Niño Southern Oscillation (ENSO), an irregular alternation between warming and cooling (lasting about two to seven years) in the equatorial Pacific Ocean that causes significant year-to-year regional and global shifts in temperature and rainfall patterns. Volcanic eruptions also alter climate, in part increasing the amount of small (aerosol) particles in the stratosphere that reflect or absorb sunlight, leading to a short-term surface cooling lasting typically about two to three years. Over hundreds of thousands of years, slow, recurring variations in Earth’s orbit around the Sun, which alter the distribution of solar energy received by Earth, have been enough to trigger the ice age cycles of the past 800,000 years.

Fingerprinting is a powerful way of studying the causes of climate change. Different influences on climate lead to different patterns seen in climate records. This becomes obvious when scientists probe beyond changes in the average temperature of the planet and look more closely at geographical and temporal patterns of climate change. For example, an increase in the Sun’s energy output will lead to a very different pattern of temperature change (across Earth’s surface and vertically in the atmosphere) compared to that induced by an increase in CO 2 concentration. Observed atmospheric temperature changes show a fingerprint much closer to that of a long-term CO 2 increase than to that of a fluctuating Sun alone. Scientists routinely test whether purely natural changes in the Sun, volcanic activity, or internal climate variability could plausibly explain the patterns of change they have observed in many different aspects of the climate system. These analyses have shown that the observed climate changes of the past several decades cannot be explained just by natural factors.

How will climate change in the future?

Scientists have made major advances in the observations, theory, and modelling of Earth’s climate system, and these advances have enabled them to project future climate change with increasing confidence. Nevertheless, several major issues make it impossible to give precise estimates of how global or regional temperature trends will evolve decade by decade into the future. Firstly, we cannot predict how much CO 2  human activities will emit, as this depends on factors such as how the global economy develops and how society’s production and consumption of energy changes in the coming decades. Secondly, with current understanding of the complexities of how climate feedbacks operate, there is a range of possible outcomes, even for a particular scenario of CO 2  emissions. Finally, over timescales of a decade or so, natural variability can modulate the effects of an underlying trend in temperature. Taken together, all model projections indicate that Earth will continue to warm considerably more over the next few decades to centuries. If there were no technological or policy changes to reduce emission trends from their current trajectory, then further globally-averaged warming of 2.6 to 4.8 °C (4.7 to 8.6 °F) in addition to that which has already occurred would be expected during the 21st century [Figure B5]. Projecting what those ranges will mean for the climate experienced at any particular location is a challenging scientific problem, but estimates are continuing to improve as regional and local-scale models advance.

Figure b5. The amount and rate of warming expected for the 21st century depends on the total amount of greenhouse gases that humankind emits. Models project the temperature increase for a business-as-usual emissions scenario (in red) and aggressive emission reductions, falling close to zero 50 years from now (in blue). Black is the modelled estimate of past warming. Each solid line represents the average of different model runs using the same emissions scenario, and the shaded areas provide a measure of the spread (one standard deviation) between the temperature changes projected by the different models. All data are relative to a reference period (set to zero) of 1986-2005. Source: Based on IPCC AR5

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Home / For Educators: Grades 6-12 / Climate Explained: Introductory Essays About Climate Change Topics

Climate Explained: Introductory Essays About Climate Change Topics

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Climate Explained, a part of Yale Climate Connections, is an essay collection that addresses an array of climate change questions and topics, including why it’s cold outside if global warming is real, how we know that humans are responsible for global warming, and the relationship between climate change and national security.

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Climate Change Basics: Five Facts, Ten Words

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Essay on Global Warming

• Updated on  
• Apr 27, 2024

Being able to write an essay is an integral part of mastering any language. Essays form an integral part of many academic and scholastic exams like the SAT , and UPSC amongst many others. It is a crucial evaluative part of English proficiency tests as well like IELTS , TOEFL , etc. Major essays are meant to emphasize public issues of concern that can have significant consequences on the world. To understand the concept of Global Warming and its causes and effects, we must first examine the many factors that influence the planet’s temperature and what this implies for the world’s future. Here’s an unbiased look at the essay on Global Warming and other essential related topics.

Short Essay on Global Warming and Climate Change?

Since the industrial and scientific revolutions, Earth’s resources have been gradually depleted. Furthermore, the start of the world’s population’s exponential expansion is particularly hard on the environment. Simply put, as the population’s need for consumption grows, so does the use of natural resources , as well as the waste generated by that consumption.

Climate change has been one of the most significant long-term consequences of this. Climate change is more than just the rise or fall of global temperatures; it also affects rain cycles, wind patterns, cyclone frequencies, sea levels, and other factors. It has an impact on all major life groupings on the planet.

Also Read: World Population Day

What is Global Warming?

Global warming is the unusually rapid increase in Earth’s average surface temperature over the past century, primarily due to the greenhouse gases released by people burning fossil fuels . The greenhouse gases consist of methane, nitrous oxide, ozone, carbon dioxide, water vapour, and chlorofluorocarbons. The weather prediction has been becoming more complex with every passing year, with seasons more indistinguishable, and the general temperatures hotter.

The number of hurricanes, cyclones, droughts, floods, etc., has risen steadily since the onset of the 21st century. The supervillain behind all these changes is Global Warming. The name is quite self-explanatory; it means the rise in the temperature of the Earth.

Also Read: What is a Natural Disaster?

What are the Causes of Global Warming?

According to recent studies, many scientists believe the following are the primary four causes of global warming:

• Deforestation 
• Greenhouse emissions
• Carbon emissions per capita

Extreme global warming is causing natural disasters , which can be seen all around us. One of the causes of global warming is the extreme release of greenhouse gases that become trapped on the earth’s surface, causing the temperature to rise. Similarly, volcanoes contribute to global warming by spewing excessive CO2 into the atmosphere.

The increase in population is one of the major causes of Global Warming. This increase in population also leads to increased air pollution . Automobiles emit a lot of CO2, which remains in the atmosphere. This increase in population is also causing deforestation, which contributes to global warming.

The earth’s surface emits energy into the atmosphere in the form of heat, keeping the balance with the incoming energy. Global warming depletes the ozone layer, bringing about the end of the world. There is a clear indication that increased global warming will result in the extinction of all life on Earth’s surface.

Also Read: Land, Soil, Water, Natural Vegetation, and Wildlife Resources

Solutions for Global Warming

Of course, industries and multinational conglomerates emit more carbon than the average citizen. Nonetheless, activism and community effort are the only viable ways to slow the worsening effects of global warming. Furthermore, at the state or government level, world leaders must develop concrete plans and step-by-step programmes to ensure that no further harm is done to the environment in general.

Although we are almost too late to slow the rate of global warming, finding the right solution is critical. Everyone, from individuals to governments, must work together to find a solution to Global Warming. Some of the factors to consider are pollution control, population growth, and the use of natural resources.

One very important contribution you can make is to reduce your use of plastic. Plastic is the primary cause of global warming, and recycling it takes years. Another factor to consider is deforestation, which will aid in the control of global warming. More tree planting should be encouraged to green the environment. Certain rules should also govern industrialization. Building industries in green zones that affect plants and species should be prohibited.

Also Read: Essay on Pollution

Effects of Global Warming

Global warming is a real problem that many people want to disprove to gain political advantage. However, as global citizens, we must ensure that only the truth is presented in the media.

This decade has seen a significant impact from global warming. The two most common phenomena observed are glacier retreat and arctic shrinkage. Glaciers are rapidly melting. These are clear manifestations of climate change.

Another significant effect of global warming is the rise in sea level. Flooding is occurring in low-lying areas as a result of sea-level rise. Many countries have experienced extreme weather conditions. Every year, we have unusually heavy rain, extreme heat and cold, wildfires, and other natural disasters.

Similarly, as global warming continues, marine life is being severely impacted. This is causing the extinction of marine species as well as other problems. Furthermore, changes are expected in coral reefs, which will face extinction in the coming years. These effects will intensify in the coming years, effectively halting species expansion. Furthermore, humans will eventually feel the negative effects of Global Warming.

Also Read: Concept of Sustainable Development

Sample Essays on Global Warming

Here are some sample essays on Global Warming:

Essay on Global Warming Paragraph in 100 – 150 words

Global Warming is caused by the increase of carbon dioxide levels in the earth’s atmosphere and is a result of human activities that have been causing harm to our environment for the past few centuries now. Global Warming is something that can’t be ignored and steps have to be taken to tackle the situation globally. The average temperature is constantly rising by 1.5 degrees Celsius over the last few years.

The best method to prevent future damage to the earth, cutting down more forests should be banned and Afforestation should be encouraged. Start by planting trees near your homes and offices, participate in events, and teach the importance of planting trees. It is impossible to undo the damage but it is possible to stop further harm.

Also Read: Social Forestry

Essay on Global Warming in 250 Words

Over a long period, it is observed that the temperature of the earth is increasing. This affected wildlife, animals, humans, and every living organism on earth. Glaciers have been melting, and many countries have started water shortages, flooding, and erosion and all this is because of global warming. 

No one can be blamed for global warming except for humans. Human activities such as gases released from power plants, transportation, and deforestation have increased gases such as carbon dioxide, CFCs, and other pollutants in the earth’s atmosphere.                                              The main question is how can we control the current situation and build a better world for future generations. It starts with little steps by every individual. 

Start using cloth bags made from sustainable materials for all shopping purposes, instead of using high-watt lights use energy-efficient bulbs, switch off the electricity, don’t waste water, abolish deforestation and encourage planting more trees. Shift the use of energy from petroleum or other fossil fuels to wind and solar energy. Instead of throwing out the old clothes donate them to someone so that it is recycled. 

Donate old books, don’t waste paper.  Above all, spread awareness about global warming. Every little thing a person does towards saving the earth will contribute in big or small amounts. We must learn that 1% effort is better than no effort. Pledge to take care of Mother Nature and speak up about global warming.

Also Read: Types of Water Pollution

Essay on Global Warming in 500 Words

Global warming isn’t a prediction, it is happening! A person denying it or unaware of it is in the most simple terms complicit. Do we have another planet to live on? Unfortunately, we have been bestowed with this one planet only that can sustain life yet over the years we have turned a blind eye to the plight it is in. Global warming is not an abstract concept but a global phenomenon occurring ever so slowly even at this moment. Global Warming is a phenomenon that is occurring every minute resulting in a gradual increase in the Earth’s overall climate. Brought about by greenhouse gases that trap the solar radiation in the atmosphere, global warming can change the entire map of the earth, displacing areas, flooding many countries, and destroying multiple lifeforms. Extreme weather is a direct consequence of global warming but it is not an exhaustive consequence. There are virtually limitless effects of global warming which are all harmful to life on earth. The sea level is increasing by 0.12 inches per year worldwide. This is happening because of the melting of polar ice caps because of global warming. This has increased the frequency of floods in many lowland areas and has caused damage to coral reefs. The Arctic is one of the worst-hit areas affected by global warming. Air quality has been adversely affected and the acidity of the seawater has also increased causing severe damage to marine life forms. Severe natural disasters are brought about by global warming which has had dire effects on life and property. As long as mankind produces greenhouse gases, global warming will continue to accelerate. The consequences are felt at a much smaller scale which will increase to become drastic shortly. The power to save the day lies in the hands of humans, the need is to seize the day. Energy consumption should be reduced on an individual basis. Fuel-efficient cars and other electronics should be encouraged to reduce the wastage of energy sources. This will also improve air quality and reduce the concentration of greenhouse gases in the atmosphere. Global warming is an evil that can only be defeated when fought together. It is better late than never. If we all take steps today, we will have a much brighter future tomorrow. Global warming is the bane of our existence and various policies have come up worldwide to fight it but that is not enough. The actual difference is made when we work at an individual level to fight it. Understanding its import now is crucial before it becomes an irrevocable mistake. Exterminating global warming is of utmost importance and each one of us is as responsible for it as the next.  

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Essay on Global Warming UPSC

Always hear about global warming everywhere, but do we know what it is? The evil of the worst form, global warming is a phenomenon that can affect life more fatally. Global warming refers to the increase in the earth’s temperature as a result of various human activities. The planet is gradually getting hotter and threatening the existence of lifeforms on it. Despite being relentlessly studied and researched, global warming for the majority of the population remains an abstract concept of science. It is this concept that over the years has culminated in making global warming a stark reality and not a concept covered in books. Global warming is not caused by one sole reason that can be curbed. Multifarious factors cause global warming most of which are a part of an individual’s daily existence. Burning of fuels for cooking, in vehicles, and for other conventional uses, a large amount of greenhouse gases like carbon dioxide, and methane amongst many others is produced which accelerates global warming. Rampant deforestation also results in global warming as lesser green cover results in an increased presence of carbon dioxide in the atmosphere which is a greenhouse gas.  Finding a solution to global warming is of immediate importance. Global warming is a phenomenon that has to be fought unitedly. Planting more trees can be the first step that can be taken toward warding off the severe consequences of global warming. Increasing the green cover will result in regulating the carbon cycle. There should be a shift from using nonrenewable energy to renewable energy such as wind or solar energy which causes less pollution and thereby hinder the acceleration of global warming. Reducing energy needs at an individual level and not wasting energy in any form is the most important step to be taken against global warming. The warning bells are tolling to awaken us from the deep slumber of complacency we have slipped into. Humans can fight against nature and it is high time we acknowledged that. With all our scientific progress and technological inventions, fighting off the negative effects of global warming is implausible. We have to remember that we do not inherit the earth from our ancestors but borrow it from our future generations and the responsibility lies on our shoulders to bequeath them a healthy planet for life to exist. 

Also Read: Essay on Disaster Management

Climate Change and Global Warming Essay

Global Warming and Climate Change are two sides of the same coin. Both are interrelated with each other and are two issues of major concern worldwide. Greenhouse gases released such as carbon dioxide, CFCs, and other pollutants in the earth’s atmosphere cause Global Warming which leads to climate change. Black holes have started to form in the ozone layer that protects the earth from harmful ultraviolet rays. 

Human activities have created climate change and global warming. Industrial waste and fumes are the major contributors to global warming. 

Another factor affecting is the burning of fossil fuels, deforestation and also one of the reasons for climate change.  Global warming has resulted in shrinking mountain glaciers in Antarctica, Greenland, and the Arctic and causing climate change. Switching from the use of fossil fuels to energy sources like wind and solar. 

When buying any electronic appliance buy the best quality with energy savings stars. Don’t waste water and encourage rainwater harvesting in your community. 

Also Read: Essay on Air Pollution

Tips to Write an Essay

Writing an effective essay needs skills that few people possess and even fewer know how to implement. While writing an essay can be an assiduous task that can be unnerving at times, some key pointers can be inculcated to draft a successful essay. These involve focusing on the structure of the essay, planning it out well, and emphasizing crucial details.

Mentioned below are some pointers that can help you write better structure and more thoughtful essays that will get across to your readers:

• Prepare an outline for the essay to ensure continuity and relevance and no break in the structure of the essay
• Decide on a thesis statement that will form the basis of your essay. It will be the point of your essay and help readers understand your contention
• Follow the structure of an introduction, a detailed body followed by a conclusion so that the readers can comprehend the essay in a particular manner without any dissonance.
• Make your beginning catchy and include solutions in your conclusion to make the essay insightful and lucrative to read
• Reread before putting it out and add your flair to the essay to make it more personal and thereby unique and intriguing for readers  

Also Read: I Love My India Essay: 100 and 500+ Words in English for School Students

Ans. Both natural and man-made factors contribute to global warming. The natural one also contains methane gas, volcanic eruptions, and greenhouse gases. Deforestation, mining, livestock raising, burning fossil fuels, and other man-made causes are next.

Ans. The government and the general public can work together to stop global warming. Trees must be planted more often, and deforestation must be prohibited. Auto usage needs to be curbed, and recycling needs to be promoted.

Ans. Switching to renewable energy sources , adopting sustainable farming, transportation, and energy methods, and conserving water and other natural resources.

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Digvijay Singh

Having 2+ years of experience in educational content writing, withholding a Bachelor's in Physical Education and Sports Science and a strong interest in writing educational content for students enrolled in domestic and foreign study abroad programmes. I believe in offering a distinct viewpoint to the table, to help students deal with the complexities of both domestic and foreign educational systems. Through engaging storytelling and insightful analysis, I aim to inspire my readers to embark on their educational journeys, whether abroad or at home, and to make the most of every learning opportunity that comes their way.

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This was really a good essay on global warming… There has been used many unic words..and I really liked it!!!Seriously I had been looking for a essay about Global warming just like this…

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I want to learn how to write essay writing so I joined this page.This page is very useful for everyone.

Hi, we are glad that we could help you to write essays. We have a beginner’s guide to write essays ( https://leverageedu.com/blog/essay-writing/ ) and we think this might help you.

It is not good , to have global warming in our earth .So we all have to afforestation program on all the world.

thank you so much

Very educative , helpful and it is really going to strength my English knowledge to structure my essay in future

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Global warming is the increase in 𝓽𝓱𝓮 ᴀᴠᴇʀᴀɢᴇ ᴛᴇᴍᴘᴇʀᴀᴛᴜʀᴇs ᴏғ ᴇᴀʀᴛʜ🌎 ᴀᴛᴍᴏsᴘʜᴇʀᴇ

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What Are the Causes of Climate Change?

We can’t fight climate change without understanding what drives it.

Low water levels at Shasta Lake, California, following a historic drought in October 2021

Andrew Innerarity/California Department of Water Resources

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At the root of climate change is the phenomenon known as the greenhouse effect , the term scientists use to describe the way that certain atmospheric gases “trap” heat that would otherwise radiate upward, from the planet’s surface, into outer space. On the one hand, we have the greenhouse effect to thank for the presence of life on earth; without it, our planet would be cold and unlivable.

But beginning in the mid- to late-19th century, human activity began pushing the greenhouse effect to new levels. The result? A planet that’s warmer right now than at any other point in human history, and getting ever warmer. This global warming has, in turn, dramatically altered natural cycles and weather patterns, with impacts that include extreme heat, protracted drought, increased flooding, more intense storms, and rising sea levels. Taken together, these miserable and sometimes deadly effects are what have come to be known as climate change .

Detailing and discussing the human causes of climate change isn’t about shaming people, or trying to make them feel guilty for their choices. It’s about defining the problem so that we can arrive at effective solutions. And we must honestly address its origins—even though it can sometimes be difficult, or even uncomfortable, to do so. Human civilization has made extraordinary productivity leaps, some of which have led to our currently overheated planet. But by harnessing that same ability to innovate and attaching it to a renewed sense of shared responsibility, we can find ways to cool the planet down, fight climate change , and chart a course toward a more just, equitable, and sustainable future.

Here’s a rough breakdown of the factors that are driving climate change.

Natural causes of climate change

Human-driven causes of climate change, transportation, electricity generation, industry & manufacturing, agriculture, oil & gas development, deforestation, our lifestyle choices.

Some amount of climate change can be attributed to natural phenomena. Over the course of Earth’s existence, volcanic eruptions , fluctuations in solar radiation , tectonic shifts , and even small changes in our orbit have all had observable effects on planetary warming and cooling patterns.

But climate records are able to show that today’s global warming—particularly what has occured since the start of the industrial revolution—is happening much, much faster than ever before. According to NASA , “[t]hese natural causes are still in play today, but their influence is too small or they occur too slowly to explain the rapid warming seen in recent decades.” And the records refute the misinformation that natural causes are the main culprits behind climate change, as some in the fossil fuel industry and conservative think tanks would like us to believe.

Chemical manufacturing plants emit fumes along Onondaga Lake in Solvay, New York, in the late-19th century. Over time, industrial development severely polluted the local area.

Library of Congress, Prints & Photographs Division, Detroit Publishing Company Collection

Scientists agree that human activity is the primary driver of what we’re seeing now worldwide. (This type of climate change is sometimes referred to as anthropogenic , which is just a way of saying “caused by human beings.”) The unchecked burning of fossil fuels over the past 150 years has drastically increased the presence of atmospheric greenhouse gases, most notably carbon dioxide . At the same time, logging and development have led to the widespread destruction of forests, wetlands, and other carbon sinks —natural resources that store carbon dioxide and prevent it from being released into the atmosphere.

Right now, atmospheric concentrations of greenhouse gases like carbon dioxide, methane , and nitrous oxide are the highest they’ve been in the last 800,000 years . Some greenhouse gases, like hydrochlorofluorocarbons (HFCs) , do not even exist in nature. By continuously pumping these gases into the air, we helped raise the earth’s average temperature by about 1.9 degrees Fahrenheit during the 20th century—which has brought us to our current era of deadly, and increasingly routine, weather extremes. And it’s important to note that while climate change affects everyone in some way, it doesn’t do so equally: All over the world, people of color and those living in economically disadvantaged or politically marginalized communities bear a much larger burden , despite the fact that these communities play a much smaller role in warming the planet.

Our ways of generating power for electricity, heat, and transportation, our built environment and industries, our ways of interacting with the land, and our consumption habits together serve as the primary drivers of climate change. While the percentages of greenhouse gases stemming from each source may fluctuate, the sources themselves remain relatively consistent.

Traffic on Interstate 25 in Denver

David Parsons/iStock

The cars, trucks, ships, and planes that we use to transport ourselves and our goods are a major source of global greenhouse gas emissions. (In the United States, they actually constitute the single-largest source.) Burning petroleum-based fuel in combustion engines releases massive amounts of carbon dioxide into the atmosphere. Passenger cars account for 41 percent of those emissions, with the typical passenger vehicle emitting about 4.6 metric tons of carbon dioxide per year. And trucks are by far the worst polluters on the road. They run almost constantly and largely burn diesel fuel, which is why, despite accounting for just 4 percent of U.S. vehicles, trucks emit 23 percent of all greenhouse gas emissions from transportation.

We can get these numbers down, but we need large-scale investments to get more zero-emission vehicles on the road and increase access to reliable public transit .

As of 2021, nearly 60 percent of the electricity used in the United States comes from the burning of coal, natural gas , and other fossil fuels . Because of the electricity sector’s historical investment in these dirty energy sources, it accounts for roughly a quarter of U.S. greenhouse gas emissions, including carbon dioxide, methane, and nitrous oxide.

That history is undergoing a major change, however: As renewable energy sources like wind and solar become cheaper and easier to develop, utilities are turning to them more frequently. The percentage of clean, renewable energy is growing every year—and with that growth comes a corresponding decrease in pollutants.

But while things are moving in the right direction, they’re not moving fast enough. If we’re to keep the earth’s average temperature from rising more than 1.5 degrees Celsius, which scientists say we must do in order to avoid the very worst impacts of climate change, we have to take every available opportunity to speed up the shift from fossil fuels to renewables in the electricity sector.

The factories and facilities that produce our goods are significant sources of greenhouse gases; in 2020, they were responsible for fully 24 percent of U.S. emissions. Most industrial emissions come from the production of a small set of carbon-intensive products, including basic chemicals, iron and steel, cement and concrete, aluminum, glass, and paper. To manufacture the building blocks of our infrastructure and the vast array of products demanded by consumers, producers must burn through massive amounts of energy. In addition, older facilities in need of efficiency upgrades frequently leak these gases, along with other harmful forms of air pollution .

One way to reduce the industrial sector’s carbon footprint is to increase efficiency through improved technology and stronger enforcement of pollution regulations. Another way is to rethink our attitudes toward consumption (particularly when it comes to plastics ), recycling , and reuse —so that we don’t need to be producing so many things in the first place. And, since major infrastructure projects rely heavily on industries like cement manufacturing (responsible for 7 percent of annual global greenhouse gas), policy mandates must leverage the government’s purchasing power to grow markets for cleaner alternatives, and ensure that state and federal agencies procure more sustainably produced materials for these projects. Hastening the switch from fossil fuels to renewables will also go a long way toward cleaning up this energy-intensive sector.

The advent of modern, industrialized agriculture has significantly altered the vital but delicate relationship between soil and the climate—so much so that agriculture accounted for 11 percent of U.S. greenhouse gas emissions in 2020. This sector is especially notorious for giving off large amounts of nitrous oxide and methane, powerful gases that are highly effective at trapping heat. The widespread adoption of chemical fertilizers , combined with certain crop-management practices that prioritize high yields over soil health, means that agriculture accounts for nearly three-quarters of the nitrous oxide found in our atmosphere. Meanwhile, large-scale industrialized livestock production continues to be a significant source of atmospheric methane, which is emitted as a function of the digestive processes of cattle and other ruminants.

Stephen McComber holds a squash harvested from the community garden in Kahnawà:ke Mohawk Territory, a First Nations reserve of the Mohawks of Kahnawà:ke, in Quebec.

Stephanie Foden for NRDC

But farmers and ranchers—especially Indigenous farmers, who have been tending the land according to sustainable principles —are reminding us that there’s more than one way to feed the world. By adopting the philosophies and methods associated with regenerative agriculture , we can slash emissions from this sector while boosting our soil’s capacity for sequestering carbon from the atmosphere, and producing healthier foods.

A decades-old, plugged and abandoned oil well at a cattle ranch in Crane County, Texas, in June 2021, when it was found to be leaking brine water

Matthew Busch/Bloomberg via Getty Images

Oil and gas lead to emissions at every stage of their production and consumption—not only when they’re burned as fuel, but just as soon as we drill a hole in the ground to begin extracting them. Fossil fuel development is a major source of methane, which invariably leaks from oil and gas operations : drilling, fracking , transporting, and refining. And while methane isn’t as prevalent a greenhouse gas as carbon dioxide, it’s many times more potent at trapping heat during the first 20 years of its release into the atmosphere. Even abandoned and inoperative wells—sometimes known as “orphaned” wells —leak methane. More than 3 million of these old, defunct wells are spread across the country and were responsible for emitting more than 280,000 metric tons of methane in 2018.

Unsurprisingly, given how much time we spend inside of them, our buildings—both residential and commercial—emit a lot of greenhouse gases. Heating, cooling, cooking, running appliances, and maintaining other building-wide systems accounted for 13 percent of U.S. emissions overall in 2020. And even worse, some 30 percent of the energy used in U.S. buildings goes to waste, on average.

Every day, great strides are being made in energy efficiency , allowing us to achieve the same (or even better) results with less energy expended. By requiring all new buildings to employ the highest efficiency standards—and by retrofitting existing buildings with the most up-to-date technologies—we’ll reduce emissions in this sector while simultaneously making it easier and cheaper for people in all communities to heat, cool, and power their homes: a top goal of the environmental justice movement.

An aerial view of clearcut sections of boreal forest near Dryden in Northwestern Ontario, Canada, in June 2019

River Jordan for NRDC

Another way we’re injecting more greenhouse gas into the atmosphere is through the clearcutting of the world’s forests and the degradation of its wetlands . Vegetation and soil store carbon by keeping it at ground level or underground. Through logging and other forms of development, we’re cutting down or digging up vegetative biomass and releasing all of its stored carbon into the air. In Canada’s boreal forest alone, clearcutting is responsible for releasing more than 25 million metric tons of carbon dioxide into the atmosphere each year—the emissions equivalent of 5.5 million vehicles.

Government policies that emphasize sustainable practices, combined with shifts in consumer behavior , are needed to offset this dynamic and restore the planet’s carbon sinks .

The Yellow Line Metro train crossing over the Potomac River from Washington, DC, to Virginia on June 24, 2022

Sarah Baker

The decisions we make every day as individuals—which products we purchase, how much electricity we consume, how we get around, what we eat (and what we don’t—food waste makes up 4 percent of total U.S. greenhouse gas emissions)—add up to our single, unique carbon footprints . Put all of them together and you end up with humanity’s collective carbon footprint. The first step in reducing it is for us to acknowledge the uneven distribution of climate change’s causes and effects, and for those who bear the greatest responsibility for global greenhouse gas emissions to slash them without bringing further harm to those who are least responsible .

The big, climate-affecting decisions made by utilities, industries, and governments are shaped, in the end, by us : our needs, our demands, our priorities. Winning the fight against climate change will require us to rethink those needs, ramp up those demands , and reset those priorities. Short-term thinking of the sort that enriches corporations must give way to long-term planning that strengthens communities and secures the health and safety of all people. And our definition of climate advocacy must go beyond slogans and move, swiftly, into the realm of collective action—fueled by righteous anger, perhaps, but guided by faith in science and in our ability to change the world for the better.

If our activity has brought us to this dangerous point in human history, breaking old patterns can help us find a way out.

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Causes and Effects of Climate Change

Fossil fuels – coal, oil and gas – are by far the largest contributor to global climate change, accounting for over 75 per cent of global greenhouse gas emissions and nearly 90 per cent of all carbon dioxide emissions. As greenhouse gas emissions blanket the Earth, they trap the sun’s heat. This leads to global warming and climate change. The world is now warming faster than at any point in recorded history. Warmer temperatures over time are changing weather patterns and disrupting the usual balance of nature. This poses many risks to human beings and all other forms of life on Earth. 

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“Verified for Climate” champions: Communicating science and solutions

Gustavo Figueirôa, biologist and communications director at SOS Pantanal, and Habiba Abdulrahman, eco-fashion educator, introduce themselves as champions for “Verified for Climate,” a joint initiative of the United Nations and Purpose to stand up to climate disinformation and put an end to the narratives of denialism, doomism, and delay.

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Are humans causing or contributing to global warming?

Yes, by increasing the abundance of greenhouse gases in the atmosphere, human activities are amplifying Earth’s natural greenhouse effect. Virtually all climate scientists agree that this increase in heat-trapping gases is the main reason for the 1.8°F (1.0°C) rise in global average temperature since the late nineteenth century. Carbon dioxide, methane, nitrous oxide, ozone, and various chlorofluorocarbons are all human-emitted  heat-trapping gases . Among these, carbon dioxide is of greatest concern to scientists because it exerts a larger overall warming influence than the  other gases combined .

Steam billows from the Intermountain Power Plant in Delta, Utah. This coal-fired plant is operated by the Los Angeles Department of Water and Power. Photo CC license by Matt Hintsa .

At present, humans are putting an estimated 9.5 billion metric tons of carbon into the atmosphere each year by burning fossil fuels, and another 1.5 billion through deforestation and other land cover changes. Of this human-produced carbon, forests and other vegetation absorb around 3.2 billion metric tons per year, while the ocean absorbs about 2.5 billion metric tons per year. A net 5 billion metric tons of human-produced carbon remain in the atmosphere each year, raising the global average carbon dioxide concentrations by about 2.3 parts per million per year. Since 1750, humans have increased the abundance of carbon dioxide in the atmosphere by nearly 50 percent.  Learn more .

USGCRP (2017). Climate Science Special Report: Fourth National Climate Assessment, Volume 1 [Wuebbles, D.J., D.W. Fahey, K.A. Hibbard, D.J. Dokken, B.C. Stewart, and T.K. Maycock (eds.)]. U.S. Global Change Research Program, Washington, DC, USA, 470 pp, doi:  10.7930/J0J964J6 .

Friedlingstein, P., Jones, M. W., O’Sullivan, M., Andrew, R. M., Hauck, J., Peters, G. P., Peters, W., Pongratz, J., Sitch, S., Le Quéré, C., Bakker, D. C. E., Canadell, J. G., Ciais, P., Jackson, R. B., Anthoni, P., Barbero, L., Bastos, A., Bastrikov, V., Becker, M., … Zaehle, S. (2019). Global carbon budget 2019. Earth System Science Data, 11(4), 1783–1838. https://doi.org/10.3929/ethz-b-000385668

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The global warming that’s causing our climate crisis is already having dire consequences.

In just the past few decades:

• Rising temperatures have worsened extreme weather events .
• Chunks of ice in the Antarctic have broken apart .
• Wildfire seasons are months longer .
• Coral reefs have been bleached of their colors .
• Mosquitoes are expanding their territory, able to spread disease .

What’s causing this climate crisis?

It’s mainly us.

Humans are the main cause of climate change — we burn fossil fuels and chop down forests, causing average temperatures to rise worldwide. That global warming trend is increasingly disrupting our climate — the average weather over many years.

Earth has already warmed by about 1 degree Celsius, or 1.8 degrees Fahrenheit, since the 19th century, before industry started to boom.

While we experience the effects , we’re on our way toward 1.5 degrees C (2.7 F) by as early as 2030.

7 facts about climate change

Why a half-degree more is such a big deal

A warmer world — even by a half-degree Celsius — has more evaporation, leading to more water in the atmosphere. Such changing conditions put our agriculture, health, water supply and more at risk.

Picture a North Carolina cotton farm that’s been around since 1960, with global average temperatures rising by roughly half a degree since it grew its first crop.

The increased evaporation and additional moisture to the atmosphere has led to 30% more intense rain during heavy downpours in that part of the U.S.

Then a hurricane like 2018’s Florence — already strengthened by warmer oceans and higher seas — dumps this excess rainfall on the farm. The crops get more flooded and damaged than they did half a century ago.

It's how you go from half-degree of warming to economic hardship.

Are record-breaking hurricanes our new normal?

There’s still time to act

Whether it’s a shift of 1.5 degrees or 2 degrees, these warming levels aren’t magic thresholds. Every rise in warming is worse for the planet than the last.

But they're not inevitable.

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How Climate Change Will Affect Plants

We human beings need plants for our survival. Everything we eat consists of plants or animals that depend on plants somewhere along the food chain. Plants also form the backbone of natural ecosystems, and they absorb about 30 percent of all the carbon dioxide emitted by humans each year. But as the impacts of climate change worsen, how are higher levels of CO2 in the atmosphere and warmer temperatures affecting the plant world?

CO2 boosts plant productivity

Plants use sunlight, carbon dioxide from the atmosphere, and water for photosynthesis to produce oxygen and carbohydrates that plants use for energy and growth.

Rising levels of CO2 in the atmosphere drive an increase in plant photosynthesis—an effect known as the carbon fertilization effect. New research  has found that between 1982 and 2020, global plant photosynthesis grew 12 percent, tracking CO2 levels in the atmosphere as they rose 17 percent. The vast majority of this increase in photosynthesis was due to carbon dioxide fertilization.

Increased photosynthesis results in more growth in some plants. Scientists have found  that in response to elevated CO2 levels, above-ground plant growth increased an average of 21 percent, while below-ground growth increased 28 percent. As a result, some crops such as wheat, rice and soybeans are expected to benefit from increased CO2 with an increase in yields from 12 to 14 percent. The growth of some tropical and sub-tropical grasses and several important crops, including corn, sugar cane, sorghum, and millet, however, are not as affected by increased CO2.

Under elevated CO2 concentrations, plants use less water during photosynthesis. Plants have openings called stomata that allow CO2 to be absorbed and moisture to be released into the atmosphere. When CO2 levels rise, plants can maintain a high rate of photosynthesis and partially close their stomata, which can decrease a plant’s water loss between 5 and 20 percent. Scientists have speculated that this could result in plants releasing less water to the atmosphere, thus keeping more on land, in the soil and streams.

But other factors count

Elevated levels of CO2 from climate change may enable plants to benefit from the carbon fertilization effect and use less water to grow, but it’s not all good news for plants. It’s more complicated than that, because climate change is also impacting other factors critical to plants’ growth, such as nutrients, temperature, and water.

Nitrogen limitations

Researchers that studied hundreds of plant species between 1980 and 2017 found that most unfertilized terrestrial ecosystems are becoming deficient in nutrients, particularly nitrogen. They attributed this decrease in nutrients to global changes, including rising temperatures and CO2 levels.

Nitrogen is the most abundant element on Earth, making up about 80 percent of the atmosphere. It is an essential element in DNA and RNA and is needed by plants to make carbohydrates and proteins for growth. However, plants cannot use the nitrogen gas found in the atmosphere because it has two atoms of nitrogen triply bonded together so tightly that they are difficult to break apart into a form plants can use. Lightning has enough energy to break the triple bond, a process called nitrogen fixation. Nitrogen is also fixed in the industrial process that produces fertilizer.

But most nitrogen fixation occurs in the soil, where certain kinds of bacteria attach to the roots of plants, such as legumes. The bacteria get carbon from the plant and in a symbiotic exchange, fix the nitrogen, combining it with oxygen or hydrogen into compounds plants can use.

Kevin Griffin , a professor in Columbia University’s Department of Ecology, Evolution and Environmental Biology and the Lamont-Doherty Earth Observatory, explained that most living things have a relatively fixed ratio between carbon and nitrogen. This means that if plants take up more CO2 to create carbohydrates because there’s more CO2 in the atmosphere, the amount of nitrogen in the leaves may be diluted, and a plant’s productivity depends on having enough nitrogen. “If you increase the CO2 around a leaf or around the plant or around the plot of forest, usually the productivity goes up,” he said. “But whether or not that increase in productivity lasts and is permanent, can be a function of whether you have [enough] nitrogen. So if nitrogen is limited, it could be that a plant just cannot use that extra CO2 and its boost in productivity can be short lived.”

Trees currently absorb about a third of human-caused CO2 emissions, but their ability to continue to do this depends on how much nitrogen is available to them. If nitrogen is limited, the benefit of increased CO2 will be limited too.

Earlier research on nitrogen fixation, based on measurements of free-living bacteria, had predicted that the fixation process works fastest at 25°C, and that as temperatures rose above 25°C, the rate of fixation would go down. In a warming world, this would have meant a runaway scenario where nitrogen fixing would decrease as temperatures rose, resulting in less plant productivity. Plants would then remove less CO2 from the atmosphere which would cause further warming and less nitrogen fixing, and so on. In a new paper , Griffin describes how he and his colleagues developed an instrument that enabled them to measure the temperature response of nitrogen on the bacteria that formed an association with the roots of plants, as opposed to on free-living bacteria.

“What we found with our new instrument looking at whole-plant symbioses in temperate and tropical trees, was that the optimal temperature for nitrogen fixation was actually about 5°C higher than any of these previous estimates, and in some cases as much as 11°C higher. This needs to be tested over a huge number of plants, but if it holds, it means that the likelihood of nitrogen fixation decreasing is much lower than we thought, which means that plants could stay more productive and prevent the runaway scenario.”

Rising temperatures

Griffin’s work also found that the temperature response of nitrogen fixation is independent from the temperature response of photosynthesis, which involves enzymes made with nitrogen. Higher temperatures can make these enzymes less efficient. Rubisco is the key enzyme that helps turn carbon dioxide into carbohydrates in photosynthesis, but as temperatures go up, it “relaxes” and the shape of its pocket that holds the CO2 gets less precise. Consequently, one fifth of the time, the enzyme winds up fixing oxygen instead of carbon dioxide, lowering the efficiency of photosynthesis and wasting the plant’s resources. With an even greater temperature increase, Rubisco can completely deactivate. Since plants respond to nitrogen fertilizer by increasing the amount of Rubisco they have and growing more, the finding that nitrogen fixation can be sustained at higher temperatures than previously thought offers the possibility that it could compensate for the decreasing efficiency of Rubisco at higher temperatures.

Rising temperatures are also causing growing seasons to become longer and warmer. Because plants will grow more and for a longer time, they will actually use more water, offsetting the benefits of partially closing their stomata. Contrary to what scientists believed in the past, the result will be drier soils and less runoff that is needed for streams and rivers. This could also lead to more local warming since evapotranspiration—when plants release moisture into the air—keeps the air cooler. In addition, when soils are dry, plants become stressed and do not absorb as much CO2, which could limit photosynthesis. Scientists found that even if plants absorbed excess carbon for photosynthesis during a wet year, the amount could not compensate for the reduced amount of CO2 absorbed during a previous dry year.

Warmer winters and a longer growing season also help the pests, pathogens, and invasive species that harm vegetation. During longer growing seasons, more generations of pests can reproduce as warmer temperatures speed up insect life cycles, and more pests and pathogens survive over warm winters. Rising temperatures are also driving some insects to invade new territories , sometimes with devastating effects for the local plants.

Higher temperatures and an increase in moisture also make crops more vulnerable. Weeds, many of which thrive in heat and elevated CO2, already cause about 34 percent of crop losses; insects cause 18 percent of losses, and disease 16 percent. Climate change will likely magnify these losses.

Many crops start to experience stress at temperatures above 32° to 35°C, although this depends on crop type and water availability. Models show that each degree of added warmth can cause a 3 to 7 percent loss in the yields of some important crops, such as corn and soybeans.

In addition, an increase in temperature speeds up the plant lifecycle so that as the plant matures more quickly, it has less time for photosynthesis, and consequently produces fewer grains and smaller yields.

Plants are also on the move in response to warming temperatures. Species that are adapted to certain climatic conditions are gradually moving north or to higher elevations where it is cooler. In the last several decades, many North American plants have moved approximately 36 feet to higher elevations or 10.5 miles to higher latitudes every 10 years. The Arctic tree line is also moving 131 to 164 feet northward towards the pole each year. New environments may be less hospitable for the species moving into them as there might be less space or more competition for resources. Some species may have nowhere left to move and ultimately, certain species will be disadvantaged by the changes while others will benefit.

Extreme weather

Climate change will bring more frequent and severe extreme weather events, including extreme precipitation, wind disturbance, heat waves, and drought. Extreme precipitation events can disturb plant growth, particularly in recently burned forests, and make plants more vulnerable to flooding and soils to erosion. More frequent high winds can stress tree stands.

Climate change is also expected to bring more combined heat waves and droughts , which would likely offset any benefits from the carbon fertilization effect. While crop yields often decrease during hot growing seasons, the combination of heat and dryness could cause maize yields to fall by 20 percent in some parts of the US, and 40 percent in Eastern Europe and southeast Africa. In addition, the combination of heat and water scarcity may reduce crop yields in places like the northern US, Canada, and Ukraine, where crop yields are projected to increase because of warmer temperatures.

Other effects of increased CO2

While some crop yields may increase, rising CO2 levels affect the level of important nutrients in crops. With elevated CO2, protein concentrations in grains of wheat, rice and barley, and in potato tubers decreased by 10 to 15 percent in one study . Crops also lose important minerals including calcium, magnesium, phosphorus, iron, and zinc. A 2018 study  of rice varieties found that while elevated CO2 concentrations increased vitamin E, they resulted in decreases in vitamins B1, B2, B5 and B9.

And, counterintuitively, the CO2-fueled increase in plant growth may result in less carbon storage in soil. Recent research found that plants have to draw more nutrients from the soil to keep up with the added growth triggered by carbon fertilization. This stimulates microbial activity, which ends up releasing CO2 into the atmosphere that might otherwise have stayed in the soil. The findings challenge the long-held belief that as plants grow more due to increased CO2, the additional biomass would turn into organic matter and soils could increase their carbon storage.

Plants face an uncertain future

Many of the studies into the response of plant life to climate change seem to suggest that most plants will be more stressed and less productive in the future. But there are still many unknowns about how the complex interactions between plant physiology and behavior, resource availability and use, shifting plant communities, and other factors will affect overall plant life in the face of climate change.

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Useful and accessible article; I’m using it to stimulate discussion in my undergraduate botany course

unlike sflint i found this confusing and wrong. I think global is good and we should make it happen more often then it does. Lets all tke action a=and make a better world

We all have our opinions. If you find it wrong, then you find it wrong. But this is a credible source. It is 99.99% right.

P.S. I only say 99.99% because nobody is 100% right.

Eco-evolutionary spatiotemporal scales, and their gradients, are going to be key. That is to say, in the real context of intense human development pressure that broadly threatens habitat and biodiversity, the destabilization and fragmentation of habitat has the potential to threaten plant communities, in combination with the background environmental changes related to climate change. It seems to me that in general, increased CO2 is going to help plants cope with elevated temperatures and water stresses; thus, my feelings are that large scale ecological conservation and recovery and the reversal of fragmentation and destructive human development patterns are increasingly important to provide ecological communities the stability – such as microclimate, needed to adapt to broader changes, and that most attention or resources should be spent reversing destructive human development which is the more direct threat. That’s also to say larger scale healthy ecoystems are more self-sustaining and will be resilient, and we should spend time and effort assisting their recovery in anticipation of potential stresses related to climate change.

Fascinating and a perfect example of benefits vs. harms. I am using this in a module on photosynthesis designed for adult learners. Thank you!

Nice piece of blog. There is a clear connection of man with nature. Man seems to be abusing this connection for his selfish needs.

You mean by growing from 1 to 8 billion people and rising. Are you repronouncing that whopping change to selfish abuse? You are here. Who exactly are you including in this sweeping comment. Everybody else but you?

I agree. When people say “man” does this or that, it means “the other guy” does it.

So you acknowledge you’re abusing this connection for YOUR selfish needs Noah. I agree, you are, we all are. It’s called survival and improvement Noah. If you don’t like it you know what to do to reduce the population.

More CO2 does the same thing in nutrient quality as more H2O does. It makes yields more abundant. And nutrient quality more dilute. What to do? As crop and soil sciences have known for decades, bring up soil fertility to balanced levels. That is important for agriculture, the part of the environment that moves nutrients into food and out of food producing areas. For the environment, those nutrients aren’t going anywhere.

Either way the earth is about 5 percent greener than it was 20 years ago.

As a student in earth and environmental science, I find this article helpful for the current curriculum. I learned a lot about climate change, and how plants can react to it.

The unanswered question in this article is ‘ What was his baseline for comparison?’ Its all very well saying yes many if not most plants will grow better and potentially faster, and balancing this positive against negatives like greater fertility and/or water requirements but this has been the case with all developments and improvements in crop varieties. More production always requires more input. Further big strawberries never taste as good or sweet as small ones, ie flavour and sugar gets diluted with increasing fruit size. But back to the baseline, what ever it is, what were crop yields like at only 280 ppm CO2. History records cold years without “summers” , failed crops and widespread famine. If it were possible to somehow return to 280 ppm CO2 would our modern crops actually produce anywhere near as much as they do. I seem to recall that some commercial greenhouses add CO2 to achieve atmospheric rates of up to 1000 ppm CO2

I find this article helpful. I see what global warming will do to our planet. It’s time to take a stand! We need to drop our CO2 levels. #GOGREEN!

A typical Phanerozoic CO2 level was about 1500 PPM and was as high as 7000 PPM. 500 million years ago. At 150 PPM of CO2 plants will die. As for global warming, it has been going on for hundreds of years. Greenland was once green and may be once again following the “little ice age.” Maybe Russia will become more hospitable. What’s the problem? If any, it would be the slow depletion of oxygen in the atmosphere.

Just accept the sky is falling. I haven’t time to explain…

I am not a scientist but one thing is abundantly clear to me , there’s more that we don’t know than there is what we do. That doesn’t mean the pursuit of knowledge is wrong , i would argue the contrary , we should pursue the truth and acknowledge it heartily when it presents itself. I found this an Interesting article , there did however seem to me that it is influenced by the politicization of this topic, we have had many doomsayers over the past years from a coming Ice age to world food shortages and my concern is that the politicization of this is being used primarily for political ends IE: there’s lots of action and posturing but little real progress , its more about optics than substance , if we were really serious we would first do what is achievable like nuclear energy and LNG , but the all or nothing mentality i currently see with the environmental groups and their dystopian views is more dangerous in my opinion than anything else.

Pursuit of knowledge is natural. Pursuit of agendas is destructive.

I am no scientist and would like to understand:

How mining of rare earth in order to cover land with solar panels to generate energy (with intense heat as a byproduct) aligns with global warming mitigation?

How does this compare to plants which absorb heat, cool the earth, store energy, provide nutrients to soil and living creatures, and are naturally occurring and self-sustaining with the ability to naturally evolve and adapt to the environment?

Is the vilification of nuclear power and carbon based energy politically (profit) driven or scientifically based?

Is there an unbiased study that shows how solar power with battery storage helps the climate and the ecological balance on earth?

How do obsolete solar panels and spent batteries polluting our earth compare to nuclear waste or elevated C02 in our atmosphere?

Can the plants that sustain our food supply, supply oxygen and cool our planet repair the damage done to the earth in support of solar energy like it can mitigate carbon in the atmosphere and maintain the life sustaining balance experienced on earth for millenniums?

We have seen plants thrive naturally at locations impacted by nuclear catastrophes. Is the same true for exhausted lithium mines, and battery and solar panel landfills? How does it compare to uranium mines? Is there a cost comparison on repairing these sites?

How much pollution is generated by mining, manufacturing, using and disposing of the current energy technologies being pushed to combat climate change compared to nuclear and carbon energy?

Does globalization help the environment or just the institutions that profit from it?

How does local production broadly across all goods and products compare to the costs to build, maintain and power global supply chains?

Is data and science unbiased when funding is agenda driven?

Is there a correlation between hysteria and fact? Harmony and hype?

Many of my same thoughts & questions but you articulated them very well. Additionally all that lithium is mined with child labor. Also, where & how are all those old solar panels & steel wind turbines being repurposed/ recycled??

Will running an electrical current in the soil promote nitrogen fixation?

You would most likely just change the soil composition by reducing and oxidizing various species in a manner that would be very difficult to predict, creating a hell of a grog. It would mess with pH and ionic concentrations and stuff I believe. To break a nitrogen-nitrogen triple bond, you would need an actual spark, lightning, to break it 🙂

Nice documentation. I really needed this kind of content. Thanks to the publisher of this amazing and interesting writing.

I think the fertilizing effect of increased CO2 far more that outweighs any concern with the heat impact that it is causing. Thank you for this article that documents its increased fertilizer value. My understanding is that CO2 has been reduced in the atmosphere over the last 2 million years due to the utilization of CaCO2 for sea shell formation which is then sequested in the crust of the earth. Would appreciate your thoughts in this regard.

As I understand it, the trend of reduction in CO2 levels in the atmosphere has been going on for about 520 million years. Which is roughly the time where sea life developed shells.

Carbon and other Green House Gases can be captured and put directly into the soil …see how this is being done in Africa with the help of the diesel tractor and how these African farmers do not use any fertilizer https://www.carbon-farmer.com/ Please do not simply dismiss the use of the diesel. Stop and think how Carbon Capture Utilization and Storage technology is becoming more and more available and economically feasible and abating the use of Diesel and other fossil fuel and to abate industries. The key word here is “ABATE”. Do not confuse the prohibition of non-ABATED fossil fuel with the use of ABATED fossil fuel. There is a huge difference. Plus think about and criticize how the minerals needed for batteries to electrify everything is causing soil degradation in a lot of places and how sand needed for glass to make solar panels and cellphones is causing sand mining to get out of control. https://youtu.be/5jyMTf3azfk?si=c_-s-TrX8dvmaVUA

Very Good Article Contains very good information

I find this to be a very interesting topic and I don’t claim to be a scientist, but everything on this earth shares in a balancing act. I didn’t read anywhere in the article about solar flares, volcanic activity, and an endless number of environmental events that contribute to the overall health of the planet. I agree with a lot of the those who commented that this is more of a political or economic driven issue than a true scientific based agenda!!

The earth was a lot warmer a thousand/million plus years ago and still coming out of the little ice age just about 500 to 600 years ago. It is just trying to get back to those days and nothing man does will stop it. Climate isn’t static. It constantly changes. You can’t control Mother Nature.

All you have to do is visit a successful greenhouse and observe the elevated level of CO2 the management spends good money to maintain in order to continue making a living. This global warming thing is falling apart despite saturation support from fake news and outright censorship by big tech.

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• Published: 04 June 2024

Global groundwater warming due to climate change

• Susanne A. Benz   ORCID: orcid.org/0000-0002-6092-5713 1 , 2 ,
• Dylan J. Irvine   ORCID: orcid.org/0000-0002-3543-6221 3 ,
• Gabriel C. Rau 4 ,
• Peter Bayer   ORCID: orcid.org/0000-0003-4884-5873 5 ,
• Kathrin Menberg 6 ,
• Philipp Blum 6 ,
• Rob C. Jamieson 1 ,
• Christian Griebler 7 &
• Barret L. Kurylyk   ORCID: orcid.org/0000-0002-8244-3838 1  

Nature Geoscience volume  17 ,  pages 545–551 ( 2024 ) Cite this article

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Aquifers contain the largest store of unfrozen freshwater, making groundwater critical for life on Earth. Surprisingly little is known about how groundwater responds to surface warming across spatial and temporal scales. Focusing on diffusive heat transport, we simulate current and projected groundwater temperatures at the global scale. We show that groundwater at the depth of the water table (excluding permafrost regions) is conservatively projected to warm on average by 2.1 °C between 2000 and 2100 under a medium emissions pathway. However, regional shallow groundwater warming patterns vary substantially due to spatial variability in climate change and water table depth. The lowest rates are projected in mountain regions such as the Andes or the Rocky Mountains. We illustrate that increasing groundwater temperatures influences stream thermal regimes, groundwater-dependent ecosystems, aquatic biogeochemical processes, groundwater quality and the geothermal potential. Results indicate that by 2100 following a medium emissions pathway, between 77 million and 188 million people are projected to live in areas where groundwater exceeds the highest threshold for drinking water temperatures set by any country.

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Earth’s climatic system warms holistically in response to the radiative imbalance from increased concentrations of greenhouse gases 1 . While the ocean absorbs most of this additional heat 2 , the terrestrial subsurface and groundwater also function as a heat sink. With a stable climate, seasonal temperature variation penetrates to a depth of 10–20 m, below which temperatures generally increase with depth in accordance with the geothermal gradient 3 . However, present-day borehole temperature–depth profiles frequently show an inversion (that is, temperature decreasing with depth) for up to 100 m due to recent, decadal surface warming 4 . Deviations from steady-state subsurface temperatures in deep boreholes (for example, >300 m) have been used to evaluate terrestrial heat storage and to estimate past, pre-observational surface temperature changes at a global scale 5 . Previous multi-continental synthesis studies on subsurface warming provide critical information on climate dynamics, but impacts on groundwater resources and associated implications are commonly ignored.

With the advent of the Gravity Recovery and Climate Experiment (GRACE) satellites, global datasets and global hydrological models, there is an emerging body of global-scale groundwater research 6 , 7 , 8 , 9 . However, global-scale groundwater studies so far have focused on resource quantity (for example, levels, recharge rates and gravity signals), whereas global-scale research into groundwater quality, including temperature, is rare. Furthermore, prominent syntheses of the relationship between anthropogenic climate change and groundwater (for example, refs. 10 , 11 ) concentrate on quantity leaving quality aspects unexplored 12 . Water temperature, sometimes known as the ‘master environmental variable’ (ref. 13 ), is an understudied groundwater quality parameter in the context of climate change.

Whereas global studies of river and lake warming have been conducted 14 , 15 , there are no global assessments of climate change impacts on groundwater temperatures (GWTs). This is despite the high importance of groundwater, which represents the largest global reservoir of unfrozen freshwater 16 , providing at least part of the water supply for half the world 17 and close to half of the global irrigation demand 18 . It also sustains terrestrial and aquatic ecosystems 19 , particularly in the face of climate change 10 . Given the role of temperature as an overarching water quality variable and observational evidence of groundwater warming in different countries in response to recent climate change 4 , 20 , 21 , the potential impact of climate warming on groundwater temperatures at a global scale remains a critical knowledge gap.

Groundwater temperature influences a suite of biogeochemical processes that alter groundwater quality 22 . For example, an increase in temperatures reduces gas solubility and raises metabolism of organisms, with an increased rate of oxygen consumption and a shift in redox conditions 23 . Because many aquifers already possess low oxygen concentrations, a small change in temperature could trigger a shift from an oxic to a hypoxic or even an anoxic regime 24 , 25 . This switch can in turn facilitate the mobilization of redox-sensitive constituents such as arsenic, manganese and phosphorus 26 , 27 . Increases in soluble phosphorus in groundwater discharging to surface water can trigger harmful algal blooms 28 , and elevated arsenic and manganese contents in potable water supplies pose direct risks to human health 29 . Groundwater warming will also cause a shift in groundwater community composition with a challenge to biodiversity and the risk of an impaired cycling of carbon and nutrients 24 , 25 . Shallow soil and groundwater warming may also cause temperatures in water distribution networks to cross critical thresholds, with potential health implications such as the growth of pathogens such as Legionella spp. 30 .

Diffusive discharge of thermally stable groundwater to surface water bodies modulates their temporal thermal regimes 30 . Also, focused groundwater inflows can create cold-water plumes that provide thermal refuge for stressed aquatic species 31 , including many prize cold-water fish. Accordingly, groundwater warming will increase ambient water temperatures in surface water bodies and the temperatures of groundwater-sourced thermal refuges. Spring ecosystems will also be affected. For example, crenobionts (true spring water species) have a very narrow temperature optimum and tolerance; hence, warming groundwater near the mouths of springs will lead to changes in their reproduction cycles, food web interactions and finally a loss of sensitive species 32 .

Groundwater warming can also have positive effects as the accumulated thermal energy can be recycled through shallow, low-carbon geothermal energy systems 33 . Whereas studies typically focus on recycling the waste heat from anthropogenic sources, particularly from subsurface urban heat islands 34 , the subsurface heat accumulating due to climate change also has the potential to sustainably satisfy local heating demands 35 . However, increased warming will make cooling systems less efficient 36 .

Here we develop and apply a global-scale heat-transport model (thermal diffusion) to quantify groundwater temperatures in space and time and their response to recent and projected climate change (Fig. 1a,b ). Our objective is to reveal the potential magnitude and long-term implications of ongoing shallow groundwater warming and to identify ‘hotspots’ of concern. The model utilizes standard climate projections to drive global groundwater warming down to 100 m below ground surface but with a focus on temperatures at the depth of the water table. We discuss (1) where aquifer warming will influence the viability of shallow geothermal heat recycling in the shallow subsurface (Fig. 1c ), (2) given how it impacts microbial activity and groundwater chemistry, where groundwater temperature may cross key thresholds set by drinking water standards (Fig. 1d ) and (3) where discharge of warmed groundwater will have the most pronounced impact on river temperatures and aquatic ecosystems (Fig. 1e ). Our model is global, and its resolution limits detailed capture of small-scale processes, producing conservative results based on tested hydraulic and thermal assumptions, including realistic advection from basin-scale recharge. More localized processes may lead to higher groundwater temperatures in areas with increased downward flow (for example, river-based recharge) or elevated surface temperatures (for example, urban heat islands) (Supplementary Note 1 provides details).

a – e , Increases in surface air and ground surface temperatures ( a ) drive increases in groundwater temperatures ( b ) that, in turn, impact the geothermal potential for shallow geothermal energy systems ( c ), groundwater chemistry and microbiology, which in turn impacts water quality ( d ) and groundwater-dependent ecosystems ( e ). Figure created with images from the UMCES IAN Media Library under a Creative Commons license CC BY-SA 4.0 .

Groundwater temperatures

We use gridded data to calculate transient subsurface temperature–depth profiles across the globe ( Methods ). Besides past and current temperatures, we present potential (modest mitigation) and worst-case (no mitigation) projections to 2100 based on the Shared Socioeconomic Pathway (SSP) 2–4.5 or SSP 5–8.5 climate scenarios of phase 6 the Coupled Model Intercomparison Project (CMIP6) (ref. 37 ). Results can be accessed and visually explored using an interactive Google Earth Engine app available at https://susanneabenz.users.earthengine.app/view/subsurface-temperature-profiles . Figure 2a–c displays maps of mean GWT at the depth of the water table and at 5 and 30 m below ground surface for 2020.

a – c , Map of modelled mean annual temperatures at the depth of the water table ( a ), at 5 m below ground surface ( b ) and at 30 m below ground surface ( c ) in 2020. d , Comparison of modelled and observed groundwater temperatures. Blue markers are (multi-) annual mean temperatures observed between 2000 and 2015 at an unspecified depth against modelled temperatures of the same time period at 30 m depth. Grey markers are temperatures of a single point in time versus modelled temperatures of the same time and depth. A histogram of the errors (observed minus modelled temperatures) is shown in the upper left corner. e , Modelled temperature–depth profiles showing mean annual temperatures and the seasonal envelope for the locations displayed in a . Please note that we use bulk thermal properties, and the water table depth is thus not an input parameter into our model.

Comparison with measured data demonstrates a good accuracy of the model given the global scale with a root mean square error of 1.4 °C and a coefficient of determination of 0.75 (Fig. 2d ). An in-depth discussion on model reliability, uncertainty and limitations is given in Supplementary Note 2 .

The median GWT at the water table in 2020 was 21.0 °C (5.6 °C, 29.3 °C; 10th, 90th percentile; Fig. 2a ). In comparison, using the same ECMWF re-analysis (ERA-5) data product, air temperatures in 2020 were lower at 17.6 °C (1.4 °C, 27.0 °C). This thermal offset is attributable to various processes and conditions including snow pack insulation in colder climates 38 and increased temperatures with depth following the geothermal gradient.

Simulated temperature–depth profiles are displayed at six example locations in Fig. 2e , including their seasonal envelope. Supplementary Note 3 provides a discussion of seasonality. Whereas all locations show an inversion of the temperature–depth profile, the depth at which this thermal gradient ‘inflection point’ (ref. 4 ) is reached varies greatly based on the rate and duration of recent climate change. At the example location in Mexico, temperatures begin to increase with depth (as expected based on the local geothermal gradient) from approximately 10 m downwards, whereas at the example location in Brazil, the inflection point reaches a depth of 45 m (Fig. 2c ). Globally, it has reached 15 (<1, 40) m (Extended Data Fig. 1a ). Heat advection from vertical groundwater flow may also influence the depth of the inflection point 4 , but only heat diffusion is considered in our model as this is the dominant heat-transport mechanism at the modelled spatial scale ( Methods ).

To better assess the impact of recent climate change on groundwater temperatures at the water table depth, we compare annual mean GWTs from 2000 and 2020. Over this 20-year period, GWTs increased on average by 0.3 (0.0, 0.8) °C (Fig. 3a ). We do not find any distinct large-scale patterns. However, some of the highest temperature increases occur in parts of Russia (for example, > + 1. 5 ∘ C north of Novosibirsk), while parts of Canada experienced cooling (for example, < −0. 5 °C in Saskatoon) between the two years. Both regions have shallow water tables, with GWTs tightly coupled to seasonal surface temperature variations and short-term intra-annual changes, rather than just the long-term surface temperature signals. As such, one hot summer can drastically alter the modelled GWT difference between 2000 and 2020. The influence of weather conditions for a given year is also notable in the depth profiles for six selected locations (Fig. 3d ). Noticeable variations occur in the upper 5 m of mean temperature range profiles with temperature changes of 1.1 °C at the location in Australia, compared with 0.5 °C at the location in Nigeria. These effects of intra-annual and short-term interannual variations in weather are attenuated at greater depths (for example, 30 m). Long-term (climate change) effects penetrate deeper, although groundwater warming may be less pronounced with depth due to the time lag between surface and subsurface temperature signals (Fig. 3c ).

a – d , Recent (2000 to 2020) changes. e – h , Projected (2000–2100) changes. a , e , Map of the change in annual mean temperature at the depth of the water table. The line in the legend indicates 0 °C. b , c , f , g , Temperature change 5 m below the land surface ( b , f ) and 30 m below the land surface ( c , g ). d , h , Change in temperatures between 2000 and 2020 ( d ) and difference between 2000 and 2100 ( h ) as depth profiles for selected locations (symbols in a and e ). Lines in h indicate median projections, whereas 25th to 75th percentiles (pct.) are presented as shading.

Over the entire century (between 2000 and 2100), groundwater warming is also projected to increase; globally averaged GWTs at the water table (at its current level) increase by 2.1 (0.8, 3.0) °C following SSP 2–4.5 median projections (Fig. 3e–g ; Extended Data Fig. 2 for 25th (1.7 (0.6, 2.5) °C) and 75th percentile (2.6 (1.0, 3.6) °C) projections) and by 3.5 (1.0, 5.5) °C following SSP 5–8.5 median projections (Extended Data Figs. 3a–d and 4 ; 25th percentile projections 3.0 (0.8, 5.8) °C; 25th percentile projections 4.6 (1.3, 7.1) °C).

We observe a clear signal of climate change by studying the depth down to which the temperature profile is reversed and temperatures are decreasing outside of seasonal effects. In 2100 the geothermal gradient inflection point is projected to reach 45 (9, 90) m on average following SSP 2–4.5 median projections (40 (6, 90) m for 25th percentile and 45 (15, 80) m for 75th percentile projections) or 60 (40, 100) m following SSP 5–8.5 median projections (60 (35, >100) m for 25th percentile and 60 (45, >100) m for 75th percentile projections; Extended Data Figs. 1b,c and 5 ).

Accumulated energy

The overall increase in GWT can be quantified as accumulated energy ( Methods ). By 2020, a net energy amount of 14 × 10 21  J has already been absorbed by the terrestrial subsurface (Fig. 4a ; 119 (45, 202) MJ m −2 ) since the beginning of the industrial revolution. In comparison, 436 × 10 21  J or about 25 times more has been absorbed by the oceans over a similar time period 39 . A review of Earth’s energy imbalance identifies a total heat gain of 358 × 10 21  J for the time period 1971–2018 only, attributing about 6% of that to land areas including permafrost regions (21 × 10 21  J, that is, a similar magnitude as our estimate) 40 . In a similar range is the 23.8 × 10 21  J that was stored in the continental landmass since 1960 following a recent study; 90% is from heat storage 41 .

a – c , Current status in 2020. d – f , Projected status in 2100 under SSP 2–4.5. a , d , Accumulated heat from the surface to 100 m depth. The line in the legend indicates 0 MJ m −2 . b , e , Map showing locations where maximum monthly GWTs at the thermal gradient inflection point (coldest depth) are above guidelines for drinking water temperatures (DWTs) 43 . c , f , GWT changes between 2000 and 2020 ( c ) and between 2000 and 2100 ( f ) at stream sites with a groundwater signature 49 . The line in the legend indicates 0 °C.

We project that by 2100 accumulated subsurface energy will be 41 × 10 21  J following SSP 2–4.5 median projections (343 (251, 463) MJ m −2 ; Fig. 4d ), 30 × 10 21  J following 25th percentile projections (255 (162, 361) MJ m −2 ) and 50 × 10 21  J following 75th percentile projections (424 (324, 560) MJ m −2 ; Extended Data Fig. 6 ). Under SSP 5–8.5 we get 62 × 10 21  J for the median projections (518 (384, 689) MJ m −2 ; Extended Data Fig. 3e ), 49 × 10 21  J for the 25th percentile projections (412 (285, 564) MJ m −2 ) and 77 × 10 21  J for the 75th percentile projections (644 (493, 844) MJ m −2 ; Extended Data Fig. 7 ). This accumulated heat can be extracted from the subsurface through wells in productive aquifers, but in lower-permeability zones and the unsaturated zone, less-efficient borehole heat exchangers would be necessary 33 . Hence, we assessed the energy accumulated in the saturated zone only (below the current water table) in Extended Data Fig. 8 —on average, there is 68 (13, 133) MJ m −2 of heat in the global subsurface saturated zone in 2020.

By comparing the accumulated aquifer thermal energy in the United States (about 45 MJ m −2 ) with local residential heating demands (about 35,000 MJ per household in 2015 following the US Energy Information Administration 2015 Energy Consumption Survey), we find that, if recycled, the energy accumulated below an average home (250 m 2 for the floor area in new single-family houses following the 2015 ‘Characteristics of new housing’ report, US Department of Commerce) in 2020 would fulfil about four months of heating demands. However, by 2100, global heat storage in the saturated zone is projected to increase to 233 (75, 363) MJ m −2 following SSP 2–4.5 and 352 (105, 536) MJ m −2 following SSP 5–8.5 median projections (Extended Data Figs. 8 and 9 for 25th and 75th percentile projections). With heating demands projected to decline due to higher temperatures and improved building insulation, recycling this subsurface heat will therefore become more feasible and is a carbon-reduced heat source that will benefit from climate change 35 . Conversely, cooling systems that rely on geothermal sources will be less efficient.

Implications for drinking water quality

Whereas groundwater warming offers benefits for geothermal heating systems, the accumulated heat also threatens water quality. In many developing countries or in poor and rural areas within developed countries, groundwater may be consumed directly without treatment or storage. It may also indirectly impact temperatures of drinking water within pipes 42 . In these regions in particular, the changes in water chemistry or microbiology that are associated with groundwater warming have to be carefully considered.

According to the World Health Organization, only 18 of 125 countries have temperature guidelines for drinking water 43 . These temperature guidelines, which are often aesthetic guidelines, range from 15 °C to 34 °C, with a median of 25 °C. Figure 4b shows where annual maximum groundwater temperatures at the geothermal gradient inflection point, that is, the most conservative depth as it is the coldest point in the temperature–depth profile, are above these thresholds in 2020. At this time, more than 29 million people live in areas where our modelled maximum GWT exceeded 34 °C. If water is extracted at the depth of the water table, this increases to close to 31 million (Extended Data Fig. 10 ). Following SSP 2–4.5 median projections by 2100, these numbers will increase to 77 million to 188 million depending on the depth of extraction (72 to 101 for 25th percentile projection; 86 to 395 for 75th percentile projections; Fig. 4d and Extended Data Figs. 5 and 9 ). Following SSP 5–8.5 median projections, 59 million to 588 million people will live in areas where maximum GWTs exceed the highest thresholds for drinking water temperatures (54 to 314 for 25th percentile projection; 66 to 1,078 for 75th percentile projections; Extended Data Figs. 3f , 6 and 9 ). Due to the different population distributions, SSP 5–8.5 projects fewer people at risk than SSP 2–4.5 for the lower estimates.

Implications for groundwater-dependent ecosystems

The ecosystems most dependent on groundwater are those in the aquifers themselves. A temperature increase may threaten groundwater biodiversity and ecosystem services 44 , 45 . Also, the increased metabolic rates of microbes caused by warming will accelerate the cycling of organic and inorganic matter, additionally fuelled by the increasing importance of dissolved organic carbon to the subsurface 46 . Combined with decreasing groundwater recharge as projected for many North African, southern European and Latin American countries 47 , this may transform oxic subsurface environments into anoxic 24 .

Groundwater warming also threatens many riverine groundwater-dependent ecosystems and the industries (for example, fisheries) that they support 48 . To capitalize on past continental-scale research related to groundwater, river temperature and ecosystems, we compare our modelled spatial patterns of groundwater warming in the conterminous United States to a recent distributed analysis of 1,729 stream sites 49 . The amplitude and phase of seasonal temperature signals in these surface water bodies were used to reveal the thermal influence and source depth of groundwater discharge to these streams, with about 40% classified as groundwater dominated. Our results show that GWT at the water table for the groundwater-dominated stream sites increased by 0.1 (0.0, 0.4) °C between 2000 and 2020 and 1.3 (0.3, 2.6) °C and 1.9 (0.4, 4.5) °C between 2000 and 2100 following SSP 2–4.5 and SSP 5–8.5 median projections, respectively (Fig. 4c,f and Extended Data Fig. 3g ). Twenty-fifth percentile projections reveal 0.7 (−0.1, 1.5) °C and 1.0 (0.0, 2.9) °C and 75th percentile projections 2.0 (0.5, 4.0) °C and 2.9 (0.6, 6.7) °C between 2000 and 2100 following SSP 2–4.5 and SSP 5–8.5, respectively (Extended Data Figs. 6 and 7 ).

The warming groundwater will inevitably raise the ambient temperature of surface water systems thermally influenced by groundwater discharge. Furthermore, such groundwater warming will even more strongly impact the thermal regimes of groundwater-fed thermal refuges (for example, at the outlets of springs or groundwater-dominated tributaries flowing into rivers) and cause them to more regularly cross critical temperature thresholds for resident species seeking relief from thermal stress. Given the connection between aquifer thermal regimes and river sediment temperatures 50 , groundwater warming also threatens the thermal suitability of benthic ecosystems and spawning areas for fish 51 , posing a major risk to fisheries and other dependent industries.

Summary and model application

In summary, global climate change is leading to increased atmospheric and surface water temperatures, both of which have already been assessed across spatial scales ranging from local to global. Here we contribute to the global analyses of environmental temperature change and of groundwater resources through the presentation of projected groundwater temperature change to 2100 at a global scale. Our analyses are based on reasonable hydraulic and thermal assumptions providing conservative estimates and allow for both the hindcasting and forecasting of groundwater temperatures. Future groundwater temperature forecasts are based on both SSP 2–4.5 and 5–8.5 climate scenarios. We provide global temperature maps at the depth of the water table, 5 and 30 m below land surface, and these highlight that places with shallow water tables and/or high rates of atmospheric warming will experience the highest groundwater warming rates globally. Importantly, given the vertical dimension of the subsurface, groundwater warming is inherently a three-dimensional (3D) phenomenon with increased lagging of warming with depth, making aquifer warming dynamics distinct from the warming of shallow or well-mixed surface water bodies.

To facilitate more detailed future analyses, the temperature maps are included in a Google Earth Engine app at https://susanneabenz.users.earthengine.app/view/subsurface-temperature-profiles . The gridded GWT output could be integrated with global river temperature models 52 to more holistically understand future warming in aquifers and connected rivers. Whereas the warming of Earth’s groundwater poses some opportunities for geothermal energy production, it increasingly threatens ecosystems and the industries depending on them, and it will degrade drinking water quality, primarily in less-developed regions.

Diffusive heat transport

We hindcast monthly subsurface temperatures (and therefore also groundwater temperatures (GWTs) based on the assumption of local equilibrium) from the surface to a depth of 100 m for the years 2000 to 2020. We also force our model with future projections following SSP 2–4.5 and SSP 5–8.5 up to the year 2100. Subsurface temperatures in the shallow crust are generally controlled by one-dimensional (1D) (vertical) diffusive heat transport. Heat advection due to water flow plays a lesser and often inconsequential role in controlling subsurface temperatures 54 , 55 , 56 , particularly at larger spatial scales that average out focused groundwater flows in faults and fractures and groundwater exchange with surface water bodies. We adopt our 1D diffusion-dominated approach rather than a 3D numerical model of coupled groundwater flow and heat transfer as there are presently neither the parameterization data nor the computing power to enable such a coupled, 3D water and thermal transport model at a global scale. Also, whereas the influence of heat advection on steady-state or transient, subsurface temperature–depth profiles can be detected with precise temperature loggers and yields valuable insight into vertical groundwater fluxes when heat is used as a groundwater tracer 57 , the rate of shallow groundwater warming is often not thought to be strongly influenced by typical basin-average, vertical groundwater flux rates. Accordingly, heat advection has been ignored in some past local-scale groundwater warming studies (for example, ref. 58 ). However, to further investigate the thermal effects of multi-dimensional flow, we run a suite of scenarios and find that advection only exerts a minor influence on groundwater warming rates for typical groundwater flow conditions (Supplementary Note 1 ), enabling us to employ our approach.

Appropriate initial conditions can be far more important for reliable simulation of temperature–depth profiles than the inclusion of heat advection 59 . To ensure our initial conditions are not influenced by any preceding climate change, we initiate our model in 1880 when the industrial revolution had not yet increased atmospheric greenhouse gasses and the climate was relatively stable. As default initial setting, we define a temperature–depth profile that increases linearly with depth z from the surface T S in accordance with the geothermal gradient a : T ( z ) =  T S  +  a z (ref. 55 ). In permafrost regions, warming above critical thresholds requires latent heat to thaw ground in addition to the sensible heat to raise the temperature. As we do not include latent heat effects, model results are not presented for permafrost regions 60 .

We use the following analytical solution to the transient 1D heat diffusion equation for a semi-infinite homogeneous medium subject to a series of n step changes in surface temperature 55 :

where j is a step change counter (counting by month), t is time, T S ( t ) is the time series of the ground surface temperature, D is the thermal diffusivity and erfc is the complementary error function. This equation is often used in an inverse manner to reconstruct pre-observational ground surface temperature history from observed, deep temperature–depth profiles, demonstrating its utility for investigating the response of subsurface thermal regimes to surface warming.

We run our model in Google Earth Engine (GEE) 61 , and the results are presented in the form of a Google Earth Engine app openly accessible at https://susanneabenz.users.earthengine.app/view/subsurface-temperature-profiles . The application presents zoomable maps of annual mean, maximum and minimum GWT at different depths and seasonal variability (maximum minus minimum) for selected years and climate scenarios. All datasets were created at a native 5 km resolution at Earth’s surface. However, Google Earth Engine automatically rescales images shown on the map based on the zoom level of the user. Charts that represent temperatures at a given location at a 5 km scale are created by clicking on the map and can be exported in CSV, SVQ or PNG file formats. For all analyses showing annual mean data at the water table depth, we first calculate monthly temperatures at the associated monthly groundwater level before averaging the results.

Ground surface temperatures

We use two distinct ground surface temperature time series: (1) one for the analysis of current (2020) temperatures based primarily on the ERA-5 data 62 and (2) one for the analysis of projected changes based on CMIP6 data 37 . On the basis of available computational power and data, we are not able to utilize monthly temperatures for the entire time period between the years 1880 and 2100. Instead, we present monthly temperatures from 1981 onwards and annual mean temperatures for 1880. The threshold 1981 is selected as ERA-5 data were available in Google Earth Engine from this point on when developing the model.

As these data are input into the analytical step function model (equation ( 1 )), we supplement them with mean temperatures of the early 1980s (that is, three-year mean 1981 to 1984) to reduce artefacts of the sudden onset of seasonal signals in our data. An example of the ground surface temperature time series is shown in Supplementary Fig. 11 .

For the analysis of current GWT, we use monthly mean soil temperature at 0–7 cm depth for the years 1981 to 2022 based on the ERA-5-Land monthly average reanalysis product 62 to form the ground surface temperature boundary condition for equation ( 1 ). These data have a native resolution of 9 km at the surface and are available through the GEE data catalogue. We also used annual ground temperature anomalies of 1880 of the top layer following the Goddard Institute for Space Studies (GISS) atmospheric model E 63 . This dataset gives the temperature difference between 1880 and 1980 in a horizontal resolution of 4° × 5° (approximately 444 km × 555 km at the equator) and can be extracted from https://data.giss.nasa.gov/modelE/transient/Rc_ij.1.11.html . To obtain absolute temperatures of 1880, we subtract the anomalies from three-year mean temperatures (1981 to 1984) of the ERA-5 data.

Future projections of ground surface temperatures are based on monthly soil temperatures closest to the surface for scenarios SSP 2–4.5 and SSP 5–8.5 from the CMIP6 programme available from 2015 to 2100. Model selection and methodology follow previous work 64 , but were updated to CMIP6 based on availability. In total we use nine models: BCC-CSM2-MR, CanESM5, GFDL-ESM4, GISS-E2-1-G, HadGEM3-GC31-LL, IPSL-CM6A-LR, MIROC6, MPI-ESM1-2-LR, NorESM2-MM. Where available, we used data from the variant label r1i1p1f1; however, for GISS-E2-1-G and HadGEM3-GC31-LL, these were not available, and we had to use r1i1p1f2 or r1i1p1f3 instead. Furthermore NorESM2-MM was missing data for January 2015; thus, we replaced them with data from December 2014 from the historic scenario. Data were collected from the World Climate Research Programme at https://esgf-node.llnl.gov/search/cmip6/ . In addition, monthly data of the historic scenario were prepared for January 1981 to December 2014 and the annual mean data for 1880. To account for the difference between the CMIP6 models and ERA-5 reanalysis, we adjust the CMIP6 outputs based on mean temperatures \(\overline{T}\) from ERA-5 between 1981 and 2014 (that is, the overlap between ERA-5 and the CMIP6 historic scenario) for each of the CMIP6 models separately as follows:

Temperatures are determined for each model before being presented as the median and the 25th and 75th percentiles.

Thermal diffusivity

For our analysis we use the ground thermal diffusivity D :

where λ (W m −1  °C −1 ) is the bulk thermal conductivity and C V (J m −3  °C −1 ) is the bulk volumetric heat capacity. Ground thermal conductivity and volumetric heat capacity for various water saturation values are derived following previous examples 35 , 65 . This method links λ and C V values for different soil and/or rock types following the VDI 4640 guidelines 66 to a global map of soil and/or rock type. This map is based on grain size information of the unconsolidated sediment map database (GUM) 67 . Where there is no available sediment class, we link to soil type in GUM. When this is also not available, we rely on the global lithological map database (GLiM) 68 . All required datasets were uploaded to Google Earth Engine in their native resolution. For assigned values, refer to Supplementary Table 1 .

We acknowledge that the distribution of subsurface thermal properties is heterogeneous. However, specific heat capacity and thermal conductivity for rocks are both well constrained to within less than half an order of magnitude 69 , 70 compared with the many orders of magnitude for hydraulic conductivity 71 . We also note that water saturation can change the individual thermal properties and have accordingly run our model for six example locations with three different diffusivity values: (1) a dry soil, (2) a moist soil (default) and (3) a water saturated soil (Supplementary Fig. 12 ). The influence of water saturation on thermal diffusivity can be complex as both the heat capacity and thermal conductivity increase with water content (equation ( 3 )). Overall, for locations with unconsolidated material in the shallow subsurface, groundwater warming rates increase with water saturation. However, the effect is nonlinear and the overall impact of water saturation on the thermal diffusivity is negligible for relative saturation values between 0.5 and 1 (ref. 72 ). A map of the diffusivity utilized here is given in Supplementary Fig. 13a .

Geothermal gradient

When advection is absent, the geothermal gradient a (°C m −1 ; equation ( 1 )) is the rate of temperature change with depth due to the geothermal heat flow Q (W m −2 ) and thermal conductivity λ (W m −1  °C −1 ):

with global values for λ derived as described earlier, and the mean heat flow Q available as a global 2° equal area grid (about 222 km at the equator) 73 . Due to their resolution, these data do not incorporate fractures and major faults, and we thus are not able to estimate groundwater temperatures at these locations properly. The grid was uploaded to GEE in its native resolution for analysis (Supplementary Fig. 13b ).

Water table depth

Much of our analysis and interpretation focuses on the future projection of temperatures at the water table depth. We therefore use the results of a previously published global groundwater model 74 , 75 with a 30 sec grid (about 1 km at the equator) to obtain the mean water table depth for 2004 to 2014. These data are available as monthly averages that we uploaded to GEE in their native resolution. In temperate climates, the model underestimates the observed water table depth by 1.5 m, and we therefore set the minimum water table depth to 1.5 m as was done in a previous study 35 . Still, whereas the global-scale hydro(geo)logical model of Fan et al. 74 , 75 can reveal large-scale patterns, it is of limited use for small-scale analysis and must be used with caution. Hence we run additional information for best- and worst-case scenarios where we add or subtract 10 m to the depth of the water table (Supplementary Note 4 ).

To calculate mean annual GWTs at the water table, temperatures for each month were determined at the corresponding water table depth by setting z in equation ( 1 ) to this depth. Future changes of water table elevation are challenging to predict, and we therefore base our analysis on the assumption that future water table elevations are unchanging. If we assume that the water table will rise, then warming would be more extreme; should the water table lower, warming as projected here is overestimated. A more detailed discussion, modelling water table changes of ± 10 m, can be found in Supplementary Note 4 . However, we note that a modelled temperature–depth profile (equation ( 1 )) is not impacted by the choice of the water table depth, and thus the results at 10 and 30 m are independent of the water table model.

Model evaluation

To assess the performance of our GWT calculations, we use two datasets of measured GWT or borehole temperatures. First, we compare our data to (multi-)annual mean shallow GWTs introduced in Benz et al. 35 . These data comprise more than 8,000 individual locations, primarily in Europe, where GWTs were measured at least twice between 2000 and 2015 at less than 60 m depth. Measurements are filtered based on their seasonal radius, a measure describing if a well was observed uniformly over the seasons and mean temperatures are therefore free of seasonal bias 76 . Second, we compare our data to temperature–depth profiles from the Borehole Temperatures and Climate Reconstruction Database at https://geothermal.earth.lsa.umich.edu/core.html . For these data, an exact date and depth of measurement are known. We filter the database based on time of measurement and depth of the first measurement, using only data taken after the year 2000 and starting at less than 30 m depth, resulting in 72 borehole measurements. To evaluate the model, we compare it to the observed groundwater temperatures described above. We compare the shallow (multi-)annual mean temperatures to mean temperatures at 30 m depth (the middle between 0 m and 60 m, the maximum depth of the observations) between 2000 and 2015. For the dataset of one-time borehole temperature–depth profiles, we compare the shallowest data points to temperatures from our model at the same depth (rounded to the nearest metre), month and year.

Example locations

We use six locations distributed over all latitudes as examples in many of our figures, with locations in Australia (longitude 149.12°, latitude −35.28°), Brazil (−47.92°, −15.77°), China (116.39°, 39.90°), Mexico (−99.12°, 19.46°), Norway (10.74°, 59.91°) and Nigeria (7.49°, 9.05°). For convenience, each point is at the location of the capital city. However, as our model is not able to adequately describe the impact of urban heat on measured groundwater temperatures, groundwater at these locations is expected to be warmer, potentially by several degrees. Our focus is on the rate of warming in response to climate change.

Depth of the geothermal gradient ‘inflection point’

To find the depth d i down to which annual mean temperature–depth profiles T ( z ) are inverted (that is, decrease with depth as opposed to increase following the geothermal gradient 4 ), we find the maximum depth where T ( d i ) >  T ( d i +1 ). Given our computational resources, we test this at a resolution of 1-m steps for the first 10 m, then in 5-m steps down to 50 m depth and lastly in 10-m steps down to the maximal depth of 100 m.

To quantify shallow subsurface accumulated energy I (J m −2 ), we compare mean annual temperature–depth profiles down to 100 m depth to the initial conditions T ( z ) =  T S ( t  = 1,880) +  a z by solving the following integral in 1-m steps:

This analysis utilizes annual mean subsurface temperatures \(\overline{T}(z)\) for 2020 or 2100 for the current and projected analyses, respectively. The volumetric heat capacity C V ( z ) of the unsaturated zone (for z above the water table) and the saturated zone (for z below the water table) uses discrete values given in Supplementary Table 1 .

Drinking water temperature thresholds

To assess the impact of groundwater warming on drinking water resources, we compare annual maximum groundwater temperatures to thresholds for drinking water temperatures summarized by the World Health Organization 43 . We do so for temperatures at the depth of the thermal gradient inflection point, the coldest point in the temperature profile and thus a best-case scenario, and for the depth of the water table to capture the 6% to 20% of wells that are no more than 5 m deeper than the water table 77 . To quantify populations at risk of exceeding the threshold, we compare the resulting maps with population counts. For temperatures in 2022, we use the 2015 United Nations-adjusted population density from the Population of World Version 4.11 Model 78 . For future scenarios, we rely on the global population projection grids for 2100 from the SSPs 79 , 80 . These data are available through the socioeconomic data and applications centre.

Impact on surface water bodies

Temperatures in surface water bodies are strongly influenced by atmospheric heat fluxes, but groundwater discharge and other processes can decouple temperatures in the atmosphere and water column. In the United States, 1,729 stream sites have been analysed by Hare et al. 49 to determine the dominance of groundwater discharge and to ascertain the relative depth (shallow or deep) of the associated aquifers. We use these sites to extract changes in mean annual groundwater temperature at the depth of the water table from our results to assess the impact of groundwater warming on these surface water bodies.

Data availability

Raster files (5 km resolution, in the GeoTIFF format) and tables (.CSV) used to create all figures of this study are made available at the Scholars Portal Dataverse at https://doi.org/10.5683/SP3/GE4VEQ (ref. 81 ). An online tool to facilitate exploration of our groundwater temperature model is available at https://susanneabenz.users.earthengine.app/view/subsurface-temperature-profiles .

Code availability

All codes used are also available at the Scholars Portal Dataverse under https://doi.org/10.5683/SP3/GE4VEQ (ref. 81 ). This includes codes written with Jupyter Notebook (Python) and Google Earth Engine (Javascript and GoogleColab/Python) and a detailed description of the process (readme.txt).

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Acknowledgements

S.A.B. was supported through a Banting postdoctoral fellowship, administered by the government of Canada, and since October 2022 as a Freigeist fellow of the Volkswagen Foundation. B.L.K. was supported through the Canada Research Chairs programme. K.M. was supported by the Margarete von Wrangell programme of the Ministry of Science, Research and the Arts Baden-Württemberg (MWK). We thank C. Tissen for sharing data she collected in her study on groundwater temperature anomalies in Europe 53 and the many other people and agencies collecting groundwater temperature data and making them available through (publicly accessible) databases. Without these data, successful validation of our method would not have been possible.

Open access funding provided by Karlsruher Institut für Technologie (KIT).

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Research Institute for the Environment and Livelihoods, Charles Darwin University, Casuarina, Northern Territory, Australia

Dylan J. Irvine

School of Environmental and Life Sciences, The University of Newcastle, Callaghan, New South Wales, Australia

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Department of Applied Geology, Martin Luther University Halle-Wittenberg, Halle, Germany

Peter Bayer

Institute of Applied Geosciences, Karlsruhe Institute of Technology, Karlsruhe, Germany

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S.A.B., B.L.K. and D.J.I. designed the study. S.A.B., B.L.K., D.J.I., G.C.R., P. Blum, K.M. and P. Bayer developed the methodology. S.A.B. prepared all data and code for analysis and designed figures. D.J.I. designed Fig. 1 . D.J.I. and G.C.R. designed, performed and led the discussion of the analysis in Supplementary Note 1 . S.A.B., B.L.K., D.J.I. and G.C.R. wrote the manuscript. All authors interpreted results and edited the manuscript together.

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Extended data

Extended data fig. 1 depth to the inflection point..

Shown is the depth down to which we can trace the impact of climate change in form of inverted temperature-depth profiles, that is temperature is decreasing with depth and not increasing with depth as expected based on the geothermal gradient. a and b , The depth to the geothermal inflection point in 2020 and 2100 following SSP 2-4.5. c , The depth to the geothermal inflection point in 2100 following SSP 5-8.5.

Extended Data Fig. 2 Change in groundwater temperatures following SSP 2-4.5, 25th and 75th percentile projections.

a – f , Map of the change in annual mean temperature between 2000 and 2100 following SSP 2-4.5 at the depth of the water table (under consideration of its seasonal variation). Temperatures in 2000 are based on the historic CMIP6 scenario. The line in the legend indicates 0 ∘ C. b and e , Annual mean groundwater temperature 5 m below the surface. c and f , Annual mean groundwater temperature 30 m below the surface. a – c , Annual mean groundwater temperature 25th percentile projected changes. d – f , Annual mean groundwater temperature 75th percentile projected changes.

Extended Data Fig. 3 Change in groundwater temperatures between 2000 and 2100 and implications following SSP 5-8.5.

a , Map of the change in annual mean temperature between 2000 and 2100 following SSP 5-8.5 (median projections) at the depth of the water table (under consideration of its seasonal variation). Temperatures in 2000 are based on the historic CMIP6 scenario. The line in the legend indicates 0 ∘ C. b , temperature change 5 m below the surface, and c , 30 m below the surface. d , Change in temperatures between 2000 and 2100 as depth profiles for selected locations. Lines indicate median projections whereas 25th to 75th percentile are presented as shading. e , Accumulated heat down to 100 m depth. The line in the legend indicates 0 MJ per m 2 . f , Map showing locations where maximum monthly GWTs at the thermal gradient inflection point (that is coldest depth) in 2100 are above guidelines for drinking water temperatures (DWTs). g , GWT changes between 2000 and 2100 at stream sites with a groundwater signature.

Extended Data Fig. 4 Change in groundwater temperatures following SSP5-8.5, 25th and 75th percentile projections.

a and d , Map of the change in annual mean temperature between 2000 and 2100 following SSP5-8.5 at the depth of the water table (under consideration of its seasonal variation). Temperatures in 2000 are based on the historic CMIP6 scenario. The line in the legend indicates 0 ∘ C. b and e , Annual mean groundwater temperature 5 m below the surface. c and f , Annual mean groundwater temperature 30 m below the surface. a to c , Annual mean groundwater temperature 25th percentile projected changes. d to f , Annual mean groundwater temperature 75th percentile projected changes.

Extended Data Fig. 5 Depth to the inflection point for 25th and 75th SSP projections.

The depth down to which we can trace the impact of climate change in form of inverted temperature-depth profiles, that is temperature is decreasing with depth and not increasing with depth as expected based on the geothermal gradient. a and b , The inflection point for SSP2-4.5 in 2100 based on 25th percentile or 75th percentile projections, respecively. c and d , The inflection point for SSP5-8.5 in 20100 based on 25th percentile or rather 75th percentile projections.

Extended Data Fig. 6 Implication of groundwater warming for SSP 2-4.5 25th and 75th percentile projections.

a and d , Accumulated heat down to 100 m depth for SSP 2-4.5 25th and 75th percentile projections, respectively. The line in the legend indicates 0 MJ per m 2 . b and e , Locations where maximum monthly GWTs at the thermal gradient inflection point (that is coldest depth) in 2100 are above guidelines for drinking water temperatures (DWTs) for SSP 2-4.5 25th and 75th percentile projections, respectively. c and f , GWT changes between 2000 and 2100 at stream sites with a groundwater signature for SSP 2-4.5 25th and 75th percentile projections, respectively.

Extended Data Fig. 7 Implication of groundwater warming for SSP 5-8.5 25th and 75th percentile projections.

a and d , Accumulated heat down to 100 m depth for SSP 5-8.5 25th and 75th percentile projections, respectively. The line in the legend indicates 0 MJ per m 2 . b and e , Locations where maximum monthly GWTs at the thermal gradient inflection point (that is coldest depth) in 2100 are above guidelines for drinking water temperatures (DWTs) for SSP 5-8.5 25th and 75th percentile projections, respectively. c and f , GWT changes between 2000 and 2100 at stream sites with a groundwater signature for SSP 5-8.5 25th and 75th percentile projections, respectively.

Extended Data Fig. 8 Accumulated heat in the saturated zone (that is, below the water table) down to 100 m depth.

a , Accumulated heat in the saturated zone in 2020. b and c , Accumulated heat in the saturated zone in 2100 following median projections of SSP2-4.5 and SSP5-8.5, respectively.

Extended Data Fig. 9 Accumulated heat in the saturated zone (defined as below the water table down to 100 m depth) and maximum temperatures (based on monthly GWTs) at the depth of the geothermal inflection point showing exceedence of guideline thresholds for drinking water temperatures (DWTs) for 25th and 75th percentile SSP projections.

a and b , Accumulated heat in the saturated zone for SSP 2-4.5 25th and 75th percentile projections, respectively. c and d , Locations where maximum temperatures exceed guideline thresholds for drinking water temperatures (DWTs) for SSP 2-4.5 25th and 75th percentile projections, respectively. e and f , Accumulated heat in the saturated zone for SSP 5-8.5 25th and 75th percentile projections, respectively. g and h , Locations where maximum temperatures exceed guideline thresholds for DWTs for SSP 5-8.5 25th and 75th percentile projections, respectively.

Extended Data Fig. 10 Locations where maximum monthly GWTs at the depth of the water table exceed guideline thresholds for drinking water temperatures (DWTs).

a , Maximum monthly GWTs at the depth of the water table in 2020. b and c , Maximum monthly GWTs at the depth of the water table in 2100 following median projections of SSP2-4.5 and SSP5-8.5, respectively.

Supplementary information

Supplementary information.

Supplementary Notes 1–4, Figs. 1–17 and Tables 1–5.

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Benz, S.A., Irvine, D.J., Rau, G.C. et al. Global groundwater warming due to climate change. Nat. Geosci. 17 , 545–551 (2024). https://doi.org/10.1038/s41561-024-01453-x

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5 ways climate change increases the threat of tsunamis, from collapsing ice shelves to sea level rise

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• Bahasa Indonesia

The enormous eruption of the underwater volcano in Tonga, Hunga Tonga-Hunga Ha'apai, triggered a tsunami that reached countries all around the Pacific rim, even causing a disastrous oil spill along 21 beaches in Peru.

In Tonga, waves about 2 metres high were recorded before the sea level gauge failed, and waves of up to 15m hit the west coasts of Tongatapu Islands, ‘Eua, and Ha’apai Islands. Volcanic activity could continue for weeks or months, but it’s hard to predict if or when there’ll be another such powerful eruption.

Most tsunamis are caused by earthquakes, but a significant percentage (about 15%) are caused by landslides or volcanoes. Some of these may be interlinked – for example, landslide tsunamis are often triggered by earthquakes or volcanic eruptions.

But does climate change also play a role? As the planet warms, we’re seeing more frequent and intense storms and cyclones, the melting of glaciers and ice caps, and sea levels rising. Climate change, however, doesn’t just affect the atmosphere and oceans, it affects the Earth’s crust as well.

Climate-linked geological changes can increase the incidence of earthquakes and volcanic eruptions which, in turn, can exacerbate the threat of tsunamis. Here are five ways this can happen.

1. Sea level rise

If greenhouse gas emissions remain at high rates, the average global sea level is projected to rise between 60 centimetres and 1.1m. Almost two thirds of the world’s cities with populations over five million are at risk.

Rising sea levels not only make coastal communities more vulnerable to flooding from storms, but also tsunamis. Even modest rises in sea level will dramatically increase the frequency and intensity of flooding when a tsunami occurs, as the tsunami can travel further inland.

For example, a 2018 study showed only a 50 centimetre rise would double the frequency of tsunami-induced flooding in Macau, China. This means in future, smaller tsunamis could have the same impact as larger tsunamis would today.

2. Landslides

A warming climate can increase the risk of both submarine (underwater) and aerial (above ground) landslides, thereby increasing the risk of local tsunamis.

The melting of permafrost (frozen soil) at high latitudes decreases soil stability, making it more susceptible to erosion and landslides. More intense rainfall can trigger landslides, too, as storms become more frequent under climate change.

Tsunamis can be generated on impact as a landslide enters the water, or as water is moved by a rapid underwater landslide.

Read more: Waves from the Tonga tsunami are still being felt in Australia – and even a 50cm surge could knock you off your feet

In general, tsunami waves generated from landslides or rock falls dissipate quickly and don’t travel as far as tsunamis generated from earthquakes, but they can still lead to huge waves locally.

In Alaska, US, glacial retreat and melting permafrost has exposed unstable slopes. In 2015, this melting caused a landslide that sent 180 million tonnes of rock into a narrow fjord, generating a tsunami reaching 193m high – one of the highest ever recorded worldwide.

Other areas at risk include northwest British Columbia in Canada, and the Barry Arm in Alaska, where an unstable mountain slope at the toe of the Barry Glacier has the potential to fail and generate a severe tsunami in the next 20 years.

3. Iceberg calving and collapsing ice shelves

Global warming is accelerating the rate of iceberg calving – when chunks of ice fall into the ocean.

Studies predict large ice shelves, such as the Thwaites Glacier in Antarctica, will likely collapse in the next five to ten years. Likewise, the Greenland ice sheet is thinning and retreating at an alarming rate.

While much of the current research focus is on the sea level risk associated with melting and collapse of glaciers and ice sheets, there’s also a tsunami risk from the calving and breakup process.

Wandering icebergs can trigger submarine landslides and tsunamis thousands of kilometres from the iceberg’s original source, as they hit unstable sediments on the seafloor.

4. Volcanic activity from ice melting

About 12,000 years ago, the last glacial period (“ice age”) ended and the melting ice triggered a dramatic increase in volcanic activity .

The correlation between climate warming and more volcanic eruptions isn’t yet well constrained or understood. But it may be related to changes in stress to the Earth’s crust as the weight of ice is removed, and a phenomenon called “ isostatic rebound ” – the long-term uplift of land in response to the removal of ice sheets.

If this correlation holds for the current period of climate warming and melting of ice in high latitudes, there’ll be an increased risk of volcanic eruptions and associated hazards, including tsunamis.

5. Increased earthquakes

There are a number ways climate change can increase the frequency of earthquakes, and so increase tsunami risk.

First, the weight of ice sheets may be suppressing fault movement and earthquakes . When the ice melts, the isostatic rebound (land uplift) is accompanied by an increase in earthquakes and fault movement as the crust adjusts to the loss of weight.

We may have seen this already in Alaska , where melting glaciers reduced the stability of faults, inducing many small earthquakes and possibly the magnitude 7.2 St Elias earthquake in 1979.

Another factor is low air pressure associated with storms and typhoons, which studies have also shown can trigger earthquakes in areas where the Earth’s crust is already under stress. Even relatively small changes in air pressure can trigger fault movements, as an analysis of earthquakes between 2002 and 2007 in eastern Taiwan identified.

So how can we prepare?

Many mitigation strategies for climate change should also include elements to improve tsunami preparedness.

This could include incorporating projected sea level rise into tsunami prediction models, and in building codes for infrastructure along vulnerable coastlines.

Researchers can also ensure scientific models of climate impacts include the projected increase in earthquakes, landslides and volcanic activity, and the increased tsunami risk this will bring.

Read more: What causes a tsunami? An ocean scientist explains the physics of these destructive waves

• Climate change
• Global warming
• Volcanic eruptions

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Climate Change: Evidence and Causes: Update 2020 (2020)

Chapter: conclusion, c onclusion.

This document explains that there are well-understood physical mechanisms by which changes in the amounts of greenhouse gases cause climate changes. It discusses the evidence that the concentrations of these gases in the atmosphere have increased and are still increasing rapidly, that climate change is occurring, and that most of the recent change is almost certainly due to emissions of greenhouse gases caused by human activities. Further climate change is inevitable; if emissions of greenhouse gases continue unabated, future changes will substantially exceed those that have occurred so far. There remains a range of estimates of the magnitude and regional expression of future change, but increases in the extremes of climate that can adversely affect natural ecosystems and human activities and infrastructure are expected.

Citizens and governments can choose among several options (or a mixture of those options) in response to this information: they can change their pattern of energy production and usage in order to limit emissions of greenhouse gases and hence the magnitude of climate changes; they can wait for changes to occur and accept the losses, damage, and suffering that arise; they can adapt to actual and expected changes as much as possible; or they can seek as yet unproven “geoengineering” solutions to counteract some of the climate changes that would otherwise occur. Each of these options has risks, attractions and costs, and what is actually done may be a mixture of these different options. Different nations and communities will vary in their vulnerability and their capacity to adapt. There is an important debate to be had about choices among these options, to decide what is best for each group or nation, and most importantly for the global population as a whole. The options have to be discussed at a global scale because in many cases those communities that are most vulnerable control few of the emissions, either past or future. Our description of the science of climate change, with both its facts and its uncertainties, is offered as a basis to inform that policy debate.

A CKNOWLEDGEMENTS

The following individuals served as the primary writing team for the 2014 and 2020 editions of this document:

• Eric Wolff FRS, (UK lead), University of Cambridge
• Inez Fung (NAS, US lead), University of California, Berkeley
• Brian Hoskins FRS, Grantham Institute for Climate Change
• John F.B. Mitchell FRS, UK Met Office
• Tim Palmer FRS, University of Oxford
• Benjamin Santer (NAS), Lawrence Livermore National Laboratory
• John Shepherd FRS, University of Southampton
• Keith Shine FRS, University of Reading.
• Susan Solomon (NAS), Massachusetts Institute of Technology
• Kevin Trenberth, National Center for Atmospheric Research
• John Walsh, University of Alaska, Fairbanks
• Don Wuebbles, University of Illinois

Staff support for the 2020 revision was provided by Richard Walker, Amanda Purcell, Nancy Huddleston, and Michael Hudson. We offer special thanks to Rebecca Lindsey and NOAA Climate.gov for providing data and figure updates.

The following individuals served as reviewers of the 2014 document in accordance with procedures approved by the Royal Society and the National Academy of Sciences:

• Richard Alley (NAS), Department of Geosciences, Pennsylvania State University
• Alec Broers FRS, Former President of the Royal Academy of Engineering
• Harry Elderfield FRS, Department of Earth Sciences, University of Cambridge
• Joanna Haigh FRS, Professor of Atmospheric Physics, Imperial College London
• Isaac Held (NAS), NOAA Geophysical Fluid Dynamics Laboratory
• John Kutzbach (NAS), Center for Climatic Research, University of Wisconsin
• Jerry Meehl, Senior Scientist, National Center for Atmospheric Research
• John Pendry FRS, Imperial College London
• John Pyle FRS, Department of Chemistry, University of Cambridge
• Gavin Schmidt, NASA Goddard Space Flight Center
• Emily Shuckburgh, British Antarctic Survey
• Gabrielle Walker, Journalist
• Andrew Watson FRS, University of East Anglia

The Support for the 2014 Edition was provided by NAS Endowment Funds. We offer sincere thanks to the Ralph J. and Carol M. Cicerone Endowment for NAS Missions for supporting the production of this 2020 Edition.

F OR FURTHER READING

For more detailed discussion of the topics addressed in this document (including references to the underlying original research), see:

• Intergovernmental Panel on Climate Change (IPCC), 2019: Special Report on the Ocean and Cryosphere in a Changing Climate [ https://www.ipcc.ch/srocc ]
• National Academies of Sciences, Engineering, and Medicine (NASEM), 2019: Negative Emissions Technologies and Reliable Sequestration: A Research Agenda [ https://www.nap.edu/catalog/25259 ]
• Royal Society, 2018: Greenhouse gas removal [ https://raeng.org.uk/greenhousegasremoval ]
• U.S. Global Change Research Program (USGCRP), 2018: Fourth National Climate Assessment Volume II: Impacts, Risks, and Adaptation in the United States [ https://nca2018.globalchange.gov ]
• IPCC, 2018: Global Warming of 1.5°C [ https://www.ipcc.ch/sr15 ]
• USGCRP, 2017: Fourth National Climate Assessment Volume I: Climate Science Special Reports [ https://science2017.globalchange.gov ]
• NASEM, 2016: Attribution of Extreme Weather Events in the Context of Climate Change [ https://www.nap.edu/catalog/21852 ]
• IPCC, 2013: Fifth Assessment Report (AR5) Working Group 1. Climate Change 2013: The Physical Science Basis [ https://www.ipcc.ch/report/ar5/wg1 ]
• NRC, 2013: Abrupt Impacts of Climate Change: Anticipating Surprises [ https://www.nap.edu/catalog/18373 ]
• NRC, 2011: Climate Stabilization Targets: Emissions, Concentrations, and Impacts Over Decades to Millennia [ https://www.nap.edu/catalog/12877 ]
• Royal Society 2010: Climate Change: A Summary of the Science [ https://royalsociety.org/topics-policy/publications/2010/climate-change-summary-science ]
• NRC, 2010: America’s Climate Choices: Advancing the Science of Climate Change [ https://www.nap.edu/catalog/12782 ]

Much of the original data underlying the scientific findings discussed here are available at:

• https://data.ucar.edu/
• https://climatedataguide.ucar.edu
• https://iridl.ldeo.columbia.edu
• https://ess-dive.lbl.gov/
• https://www.ncdc.noaa.gov/
• https://www.esrl.noaa.gov/gmd/ccgg/trends/
• http://scrippsco2.ucsd.edu
• http://hahana.soest.hawaii.edu/hot/

Climate change is one of the defining issues of our time. It is now more certain than ever, based on many lines of evidence, that humans are changing Earth's climate. The Royal Society and the US National Academy of Sciences, with their similar missions to promote the use of science to benefit society and to inform critical policy debates, produced the original Climate Change: Evidence and Causes in 2014. It was written and reviewed by a UK-US team of leading climate scientists. This new edition, prepared by the same author team, has been updated with the most recent climate data and scientific analyses, all of which reinforce our understanding of human-caused climate change.

Scientific information is a vital component for society to make informed decisions about how to reduce the magnitude of climate change and how to adapt to its impacts. This booklet serves as a key reference document for decision makers, policy makers, educators, and others seeking authoritative answers about the current state of climate-change science.

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How did a sudden reduction in shipping pollution inadvertently stoke global warming?

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A major shift in global shipping regulations intended to improve air quality may have temporarily — and inadvertently — set off a geoengineering reaction that is warming the planet, new research has found.

In January 2020, the International Maritime Organization substantially reduced the amount of harmful sulfur dioxide content allowed in shipping fuel . The move was part of a broad strategy to improve public health.

By reducing sulfur dioxide and fine particulate matter spewed by ships, the change would help reduce strokes, asthma, lung cancer, and other diseases suffered by people who live in and around ports.

But the change also had an unexpected consequence: In the past, dirtier ship emissions contributed to the creation of bright clouds over the ocean. These bright clouds helped to reflect some of the sun’s light and energy back into space. When sulfur dioxides were reduced, however, it resulted in fewer bright clouds, so more of the sun’s heat and energy were able to reach Earth’s surface, contributing to global warming.

Aggressive and impactful reporting on climate change, the environment, health and science.

The added energy gain from all that sunlight, sometimes referred to as climate forcing, contributed to anomalously high global temperatures in 2023 — the planet’s hottest year on record — and the current 12-month streak of record-hot months , according to a study published recently in the journal Communications Earth & Environment .

What’s more, researchers say this “dimming” of cloud cover could lead to a doubling or more of the warming rate in the 2020s compared with the rate since 1980.

“The results turned out to be pretty significant,” said Tianle Yuan, the study’s lead author and a senior research scientist at the University of Maryland Baltimore County and NASA’s Goddard Space Flight Center. “Because of the dimmer clouds, we effectively gained more energy to the climate system because more sunlight is coming in.”

The effect is the opposite of what happens during volcanic eruptions, which are known to temporarily cool the planet by spewing sun-blocking sulfur dioxide into the atmosphere. Sulfur dioxide, a reactive gas found in many marine fuels, is also released when those fuels are burned.

The fuel regulation sought to reduce the upper limit on the sulfur content of ships’ fuel oil from 3.5% to 0.5% . This change resulted in a roughly 80% reduction in harmful sulfur dioxide emissions from ships worldwide.

But the change also created an “inadvertent geoengineering termination shock with global impact,” the study says. Some of the strongest impacts were found in the North Atlantic, which began experiencing record-warm sea surface temperatures in 2023 .

Yuan said it is challenging to calculate the specific temperature increase associated with the new fuel regulation, because there are so many variables affecting the climate system, including El Niño. However, by modeling the forcing alone, his team found that the change could lead to an increase of 0.16 of a degree Celsius within the next seven years.

“The warming effect is consistent with the recent observed strong warming in 2023 and expected to make the 2020s anomalously warm,” the study says.

Climate & Environment

Earth breaks heat and CO₂ records once again: ‘Our planet is trying to tell us something’

Global average temperatures and CO₂ levels continue to soar. May was Earth’s 12th consecutive hottest month on record, officials announced this week.

June 5, 2024

Not everyone agrees with the findings, however.

While there is broad consensus that the change in shipping regulations contributed to some planetary warming, the magnitude of that change is not yet settled science, according to Zeke Hausfather, a climate scientist with Berkeley Earth, who noted that different models lead to a wide range of findings.

“They used a very simple model,” he said. “And in the real world, we know from more complex climate models and from historical relationships between forcing and warming, that there’s bigger lags in the system, and that not as much warming is going to be realized as quickly as they assumed.”

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At least three other upcoming studies on the regulation change found different results, both in terms of additional heat entering the climate system and in terms of temperature, ranging from 0.03 to 0.2 degree Celsius of warming — or less than half as much to an amount that’s even higher.

“What this illustrates is the way that science works when you find a new problem like this,” Hausfather said. “A bunch of different teams approach it using slightly different approaches, and they get different results.”

He said climate researchers will now work to synthesize the different models and studies, which could mean another year or two before any conclusions are drawn.

“I think everyone is pointed in the right direction here. This had an effect — it was not a negligible effect — but exactly how big it is is something we still need to work out as a community,” he said. “I don’t think we’re actually going to know the answer, for sure, for a while here.”

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April 22, 2024

That the shipping regulation change simultaneously benefited public health and worsened global warming is also not lost on those studying the problem.

Short-term exposure to sulfur dioxide can harm the human respiratory system. Larger, long-term concentrations in the air can contribute to the formation of fine particulate matter , which can penetrate the lungs and enter the bloodstream, leading to significant cardiovascular and pulmonary health problems, according to the Environmental Protection Agency.

Recent decades have already seen broad efforts to reduce sulfur emissions, including regulations dating back to the 1990s to address acid rain , another of its byproducts. But ship emissions continued to pose health threats, and a 2016 study estimated that not reducing ship sulfur limits by 2020 would contribute to more than 570,000 additional premature deaths worldwide between 2020 and 2025.

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“No one wants millions of people to die a year from air pollution, even though it has a cooling benefit to the climate,” Hausfather said.

Daniele Visioni, an assistant professor of Earth and Atmospheric Sciences at Cornell University, said similarly that the International Maritime Organization’s regulation “just made sense.”

“Air quality is a much bigger killer, and in a much more uneven way, than a small contribution to warming, and so it makes perfect sense to improve air quality,” he said. “These kind of studies should in no way be seen as a way to say we should stop improving our air. On the other hand, it does highlight the fact that the climate system is complex, and that no policy is perfect.”

Visioni is co-author of one of the upcoming papers on the matter, which is available for pre-print review . It came to some conclusions that mirrored Yuan’s — including that the shipping regulation change could lead to 0.2 of a degree Celsius of warming by 2030.

It also looked backward to try to determine how big of a role the sulfur reduction played in 2023’s extreme warmth , concluding that the regulation change “can be considered as a primary contributor” capable of explaining the anomaly. It also found that the regulation made 2023’s temperatures about 10 times more likely than if the change hadn’t occurred.

“We got definitely unlucky with a warm year, but this contribution from shipping emissions sort of pushed it toward the world record,” Visioni said.

However, not even that finding is agreed upon. Another recent study determined that 91% of last year’s heat burst was because of climate change and 8% because of El Niño, but said the reduction in sulfur emissions was effectively canceled out by emissions from raging wildfires.

While Visioni disagreed with that finding, he said it all adds to a growing body of work about the ways in which human activities shape the environment.

“We need more and not less of these kind of experiments, because we need a much better grasp and a much better understanding of how aerosols from human emissions, whether inadvertent or advertent, affect clouds and then affect the climate,” he said.

‘Humbling, and a bit worrying’: Scientists fail to fully explain record global heat

Blistering global temperatures have one NASA scientist warning: ‘We could be in uncharted territory.’ Others aren’t so sure.

March 27, 2024

Indeed, Yuan’s paper says the regulation’s undeniable warming influence makes a case that some geoengineering techniques could work, noting that “marine cloud brightening may be a viable geoengineering method in temporarily cooling the climate.”

Marine cloud brightening is a controversial form of atmospheric manipulation that uses sea salt particles to increase the reflectivity of clouds in order to cool the planet — effectively mimicking what happens during volcanic eruptions. Last week, the Alameda City Council voted unanimously to halt plans from researchers at the University of Washington to test the concept off the coast of San Francisco.

Yuan said its scientific viability does not equate to an endorsement.

“Our point is not trying to advocate that we should do this — we are kind of advocating that we should understand these aspects much better before we make a decision, because temperature is just one metric, and it’s not enough,” he said.

In fact, temperature changes are just one of many potential outcomes of marine cloud brightening and other forms of geoengineering. It can also affect weather systems, monsoons and other precipitation patterns in a manner that is not evenly distributed across the globe, creating “winners and losers,” he said.

What’s more, many conversations around geoengineering tend to ignore the underlying problem — that the vast majority of climate change continues to stem from carbon emissions tied to the burning of fossil fuels .

While cloud brightening and other efforts might lead to temporary cooling, they should not be a replacement for efforts to scale back on those emissions, Yuan said.

“Because this tool has both beneficial and adverse consequences, we should study and understand them well before we get into this,” he said. “But in the end, it’s not a long-term solution, because it’s not addressing the driver that is fundamental to climate change.”

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Paragraph on the Effects of Global Warming

Ai generator.

In a somber paragraph, the effects of global warming, spurred by climate change , loom large. Deforestation compounds this crisis, releasing carbon dioxide into the atmosphere and disrupting ecosystems. Paragraph Rising temperatures fuel extreme weather events, imperiling lives and livelihoods. Urgent action is imperative to mitigate these consequences and safeguard the planet for future generations.

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Short Paragraph on the Effects of Global Warming

Global warming has far-reaching effects on the environment and human life. Rising temperatures lead to more frequent and severe weather events, such as hurricanes, droughts, and heatwaves. Melting polar ice caps and glaciers contribute to rising sea levels, threatening coastal communities. Additionally, global warming disrupts ecosystems, endangering wildlife and biodiversity.

Medium Paragraph on the Effects of Global Warming

The effects of global warming are increasingly evident and alarming, impacting the environment, human health, and economies. As global temperatures rise, we experience more frequent and intense weather events, including hurricanes, droughts, and heatwaves. Melting polar ice caps and glaciers contribute to rising sea levels, which threaten coastal communities and increase the risk of flooding. Furthermore, global warming disrupts ecosystems, leading to habitat loss and endangering wildlife. The shifting climate also affects agriculture, reducing crop yields and exacerbating food insecurity. Human health is impacted through increased heat-related illnesses and the spread of diseases. Addressing global warming requires urgent action to reduce greenhouse gas emissions and mitigate its devastating effects.

Long Paragraph on the Effects of Global Warming

The effects of global warming are profound and multifaceted, posing significant challenges to the environment, human health, and global economies. One of the most noticeable impacts is the increase in frequency and intensity of extreme weather events, such as hurricanes, droughts, heatwaves, and heavy rainfall. These events cause widespread damage to infrastructure, disrupt communities, and result in substantial economic losses. The melting of polar ice caps and glaciers due to rising temperatures leads to rising sea levels, which threaten coastal cities and small island nations with increased flooding and erosion. Additionally, global warming disrupts natural ecosystems, causing shifts in habitat ranges and endangering species that cannot adapt quickly enough. Coral reefs, which are vital to marine biodiversity, are particularly vulnerable to ocean warming and acidification. Agricultural productivity is also affected, as changing weather patterns and increased temperatures reduce crop yields and lead to food shortages. Human health suffers from the spread of vector-borne diseases, heat-related illnesses, and respiratory issues due to increased air pollution. Furthermore, global warming exacerbates social inequalities, as vulnerable populations bear the brunt of its impacts. Addressing these challenges requires concerted global efforts to reduce greenhouse gas emissions, implement sustainable practices, and develop adaptive strategies to mitigate the far-reaching effects of global warming.

Tone-wise Paragraph Examples on the Effects of Global Warming

Formal tone.

The effects of global warming are extensive and multifaceted, significantly impacting the environment, human health, and global economies. Rising temperatures contribute to the increased frequency and intensity of extreme weather events, such as hurricanes, droughts, and heatwaves, causing widespread damage and economic losses. Melting polar ice caps and glaciers lead to rising sea levels, threatening coastal communities with flooding and erosion. Additionally, global warming disrupts ecosystems, endangering species and altering habitats. Agricultural productivity is affected by changing weather patterns, leading to food shortages. Human health is compromised by the spread of diseases and heat-related illnesses. Addressing these issues necessitates urgent, coordinated global action to reduce greenhouse gas emissions and develop adaptive strategies.

Informal Tone

Global warming is having some pretty serious effects on our planet and our lives. We’re seeing more intense weather events like hurricanes and heatwaves, and the melting ice caps are causing sea levels to rise, which threatens coastal areas. Wildlife and ecosystems are also being disrupted, and crops are suffering from changing weather patterns. Plus, our health is at risk from heat-related illnesses and spreading diseases. We need to act quickly to cut down on greenhouse gas emissions and tackle these problems.

Persuasive Tone

Consider the urgent and wide-ranging effects of global warming on our planet. Rising temperatures lead to more extreme weather events like hurricanes and droughts, causing significant damage and economic loss. Melting ice caps result in rising sea levels, threatening coastal communities. Wildlife and ecosystems are disrupted, and agriculture suffers, leading to food shortages. Our health is also at risk from heat-related illnesses and spreading diseases. We must take immediate action to reduce greenhouse gas emissions and implement sustainable practices to mitigate these impacts and protect our future.

Reflective Tone

Reflecting on the effects of global warming, it becomes clear how deeply it impacts our world. The increase in extreme weather events, melting ice caps, and rising sea levels highlight the environmental challenges we face. Wildlife and ecosystems are under threat, and agriculture is struggling with changing weather patterns. Human health is also affected by heat-related illnesses and the spread of diseases. Addressing global warming requires us to rethink our actions and prioritize sustainable practices to protect our planet and future generations.

Inspirational Tone

Embrace the challenge of combating the effects of global warming to protect our planet for future generations. Global warming leads to extreme weather events, melting ice caps, and rising sea levels, threatening our environment and communities. Wildlife and ecosystems are disrupted, and agriculture faces new challenges. Our health is also at risk. Let us come together to reduce greenhouse gas emissions, adopt sustainable practices, and inspire others to take action. By working collectively, we can mitigate these impacts and ensure a healthier, more sustainable world for all.

Optimistic Tone

The effects of global warming are significant, but we have the power to make a difference. Rising temperatures cause extreme weather, melting ice caps, and rising sea levels, but by reducing greenhouse gas emissions, we can mitigate these impacts. Wildlife and ecosystems can recover, and sustainable agricultural practices can adapt to changing weather patterns. Our health can improve with cleaner air and better preparedness for heat-related illnesses. Together, we can create a more sustainable future and protect our planet.

Urgent Tone

The effects of global warming demand immediate attention and action. Rising temperatures lead to more frequent and severe weather events, such as hurricanes, droughts, and heatwaves, causing extensive damage and economic loss. Melting ice caps result in rising sea levels, threatening coastal communities. Wildlife and ecosystems are under threat, and agriculture suffers, leading to food shortages. Human health is at risk from heat-related illnesses and spreading diseases. We must act now to reduce greenhouse gas emissions and implement sustainable practices to combat these urgent issues and safeguard our future.

Word Count-wise Effects of Global Warming Paragraph Examples

The effects of global warming are increasingly evident and alarming, impacting how we communicate, access information, and entertain ourselves. Platforms such as Facebook, Twitter, and Instagram enable us to stay connected with friends and family, no matter the distance. They provide a space for sharing experiences, photos, and updates, fostering a sense of community. Social media also serves as a powerful tool for news dissemination, allowing users to stay informed about global events in real time. Moreover, it offers various forms of entertainment, from funny videos to engaging content creators.

The effects of global warming are profound and multifaceted, posing significant challenges to the environment, human health, and global economies. One of the most noticeable impacts is the increase in frequency and intensity of extreme weather events, such as hurricanes, droughts, heatwaves, and heavy rainfall. These events cause widespread damage to infrastructure, disrupt communities, and result in substantial economic losses. The melting of polar ice caps and glaciers due to rising temperatures leads to rising sea levels, which threaten coastal cities and small island nations with increased flooding and erosion. Additionally, global warming disrupts natural ecosystems, causing shifts in habitat ranges and endangering species that cannot adapt quickly enough.

The effects of global warming are profound and multifaceted, posing significant challenges to the environment, human health, and global economies. One of the most noticeable impacts is the increase in frequency and intensity of extreme weather events, such as hurricanes, droughts, heatwaves, and heavy rainfall. These events cause widespread damage to infrastructure, disrupt communities, and result in substantial economic losses. The melting of polar ice caps and glaciers due to rising temperatures leads to rising sea levels, which threaten coastal cities and small island nations with increased flooding and erosion. Additionally, global warming disrupts natural ecosystems, causing shifts in habitat ranges and endangering species that cannot adapt quickly enough. Coral reefs, which are vital to marine biodiversity, are particularly vulnerable to ocean warming and acidification.

The effects of global warming are profound and multifaceted, posing significant challenges to the environment, human health, and global economies. One of the most noticeable impacts is the increase in frequency and intensity of extreme weather events, such as hurricanes, droughts, heatwaves, and heavy rainfall. These events cause widespread damage to infrastructure, disrupt communities, and result in substantial economic losses. The melting of polar ice caps and glaciers due to rising temperatures leads to rising sea levels, which threaten coastal cities and small island nations with increased flooding and erosion. Additionally, global warming disrupts natural ecosystems, causing shifts in habitat ranges and endangering species that cannot adapt quickly enough. Coral reefs, which are vital to marine biodiversity, are particularly vulnerable to ocean warming and acidification. Agricultural productivity is also affected, as changing weather patterns and increased temperatures reduce crop yields and lead to food shortages. Human health suffers from the spread of vector-borne diseases, heat-related illnesses, and respiratory issues due to increased air pollution.

Text prompt

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20 Examples of Gas lighting

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A climate scientist questioned his findings. It didn’t go well.

• Deep Read ( 15 Min. )
• By Stephanie Hanes Staff writer @stephaniehanes

June 6, 2024

Last year, a climate scientist named Patrick Brown, along with seven co-authors, published a study in the journal Nature about the connections between wildfires in California and global warming.

But a month later, Dr. Brown confessed in a Free Press article that he had framed his research not just to reflect the truth, but to fit within what he described as the climate alarmist storyline preferred by prestigious journals in the United States.

Why We Wrote This

Despite a wide consensus about climate change, many people remain skeptical. Can climate scientists earn back the public’s trust?

Climate advocates skewered Dr. Brown as being everything from unhinged to unethical. But he says it was only fair for him to delve into his own decision-making process as part of an honest critique of the culture within his field.

“I think there is a certain section of the population that has way too little trust in climate science, and then a section that has too much trust in a perception of what climate science is, that it’s this all-encompassing thing that tells global society what to do,” he says. 

His experience is illustrative of how difficult it can be to maintain a more nuanced stance in today’s crisis-driven world of climate science.

“On a fundamental level, some amount of skepticism is appropriate, wanted, in science,” says Lauren Kurtz, executive director of the Climate Science Legal Defense Fund. “At the same time, I think that approach has been weaponized by people who want to dispute the scientific reality of climate change, sometimes from a very disingenuous perspective.”

In late August of last year, a climate scientist named Patrick Brown, along with seven co-authors, published a study in the journal Nature about the connections between wildfires in California and global warming.

Their paper was, in many ways, standard fare for the prestigious journal. It took a deep dive into environmental measurements; it used machine learning and evaluated complex climatic comparisons; it concluded that climate change was making wildfires more extreme.

It was also, Dr. Brown claimed publicly just a month later, untrustworthy.

Dr. Brown confessed in a Free Press article that he had framed his research not just to reflect the truth, but to fit within what he described as the climate alarmist storyline preferred by prestigious journals in the United States. He did this, he says, by intentionally focusing only on climate as a factor in wildfires, and not on the myriad other causes that contribute to the blazes consuming ever more land across the country.

It wasn’t that he was hiding anything, or that the research was wrong. It was just that the paper was deliberately focused in one narrow direction – the direction most likely, he claimed, to capture the attention of journal editors.

The formula for getting published, he wrote, “is more about shaping your research in specific ways to support pre-approved narratives than it is about generating useful knowledge for society.” And when it comes to climate science, he alleged, that preapproved narrative is that “climate change impacts are pervasive and catastrophic.”

Almost immediately, people who questioned the reality of climate change began citing Dr. Brown’s essay as “proof” that global warming is a hoax, perpetrated by academics consumed by a “woke” agenda. 

The reaction was also swift within his field. The editors of Nature denied any bias and said that Dr. Brown had “poor research practices” and was “highly irresponsible.” They pointed to a number of articles that seemed to go against Dr. Brown’s assertions. And climate advocates skewered Dr. Brown as being everything from unhinged to unethical. His words, they said, would bolster what watchdog groups say is a new wave of climate denialism. 

“We’ll be hearing echoes of Brown’s impulsively emotional blurt for a very long time,” wrote Doug Bostrom on the website Skeptical Science, which was created to debunk climate misinformation. “Brown has caused durable material harm to climate progress. It’s to no good end.”

But privately, Dr. Brown insists, fellow researchers have expressed sympathy. He was never questioning the reality of climate change itself, he says, or its importance. Neither was he making up data or violating academic standards – nothing about his paper, he points out, has required a retraction. He was just pointing out a place where he saw the scientific community not living up to science’s own ideals. 

Dr. Brown, co-director of the Climate and Energy Team at The Breakthrough Institute, a research center in Berkeley, California, has long been fascinated by the way research transforms into widespread knowledge. How does the stew of individuals and institutions and media each combine in various ways to form popular understandings?

He and his co-authors had decided to focus on the real impacts of climate factors on wildfires. But they had also decided to not focus on some of the other factors that have equally real impacts. These include land-use choices and varying forest management policies. 

Their findings were sound. But as he reflected on this work, Dr. Brown says, he had to admit that he chose to focus on climate instead of other factors because he believed that’s what would make his study more likely to be published.

He thought it was only fair for him to delve into his own decision-making process as part of an honest, and important, critique of the culture within his field.

A more nuanced stance, however, can be difficult to maintain in today’s crisis-driven world of climate science.

Indeed, this is a field where researchers face increasing attacks from politicians, organizations funded by the fossil fuel industry, and social media trolls. In other words, tension is high, and, many believe, the stakes are even higher.

“Deniers and skeptics say climate scientists are alarmist. We are not alarmist enough,” says Astrid Caldas, senior scientist for community resilience at the Union of Concerned Scientists. “If we could, we would scream to the four winds and say, ‘People, wake up! Things are not looking good.’”

But if climate science doesn’t make space for alternative viewpoints, it risks its foundational ideals of open inquiry and debate and rigorous, evidence-based critiques, some analysts say. And while there is an important distinction between asking honest, skeptical questions and purveying false narratives, it’s not always crystal clear where that line lies.

Questioning mainstream assumptions about climate change without denying its import or reality – “threading the needle,” as Dr. Brown puts it – can be a much-maligned path.

“I don’t think he was prepared for the anger and vitriol,” says Roger Pielke Jr., professor at the University of Colorado Boulder. Dr. Pielke has been labeled a climate change denier himself – a characterization he vehemently rejects. “He didn’t say anything wrong. All of us think about, how do we construct our papers so we have the best chance of getting published? The climate space is no different.”

The role of uncertainty in climate science

Except, many scientists insist, it is different.

There are few scientific topics so complicated, with so many potential impacts on humanity, as climate change. And there are few areas of science that have been so undermined.

Science historians often point to the late 1800s as the moment when researchers began recognizing that the Earth was warmer than it should be, and when they began connecting this to carbon dioxide, one of the main gases that trap heat within the atmosphere. 

Since then, scientists have repeatedly measured and analyzed the Earth’s rising temperatures, as well as the impact of increasing greenhouse gases, and in particular CO 2 , which is released when humans burn fossil fuels. They have found, with increasing precision and surety, that the emissions of the modern world have indeed heated the Earth.

This is a point worth emphasizing, since this is as close to fact as one often gets in science. We know the Earth is getting hotter. We know human activity has played a significant role.

“It has as solid evidence as gravity,” says Benjamin Houlton, dean of the College of Agriculture and Life Sciences at Cornell University. There are valid scientific debates about the consequences of this heating, he says. “The uncertainty is pretty significant; there’s nothing settled about the future” – but only a scattered handful of outliers still argues against the overwhelming evidence that the planet is warming.

Still, those skeptics have had an outsize impact on Americans’ trust in climate science. And that may be intentional, some argue.

In their widely acclaimed 2010 book, “Merchants of Doubt,” Naomi Oreskes and Erik Conway detail how a small group of scientists denied connections between smoking and lung cancer, sulfur dioxide and acid rain, and aerosols and ozone damage. Their goal was often to slow down government regulation. Today, some of these same scientists have been connected to climate denial movements funded by intensely free-market, anti-environmentalist organizations.

The partisanship around global warming has eased some in recent years. More than half of younger Republicans say the government is doing too little to reduce the effects of climate change, according to the Pew Research Center. But the difference between Republicans and Democrats is still stark. 

Gavin Schmidt is a NASA climate scientist who in 2021 served as the agency’s acting senior adviser on climate. He says that many of his colleagues were taken aback when partisanship crashed into their profession.

When he got his Ph.D. in the early 1990s, he recalls, the question of global warming was politically salient, but the scientists studying it were, well, scientists. They were individuals interested in the fascinating but seemingly esoteric qualities of clouds and dinosaurs, of ice cores and carbon. “It was a bit of a niche thing,” he says. He and his colleagues were happy to work in the lab and the field, focused on calculations and peer-reviewed journals. For the most part, they didn’t see public debate and policymaking as part of their world.

And then that started to change.

In 1995, a controversy exploded around the Intergovernmental Panel on Climate Change’s second assessment report, which for the first time stated that “the balance of evidence suggests a discernible human influence on global climate.”

Free market think tanks and policymakers, along with some scientists connected to these groups, accused climate modeler Ben Santer, a co-author of the report, of professional dishonesty, saying he skewed his research for political reasons, The allegations soon became personal and increasingly threatening. At one point the scientist found a dead rat left on his doorstep. It didn’t matter that Dr. Santer and his colleagues repeatedly debunked the accusations. The harassment still remained virulent.

In 1998, a scientist named Michael Mann published a graph in Nature magazine shaped like a hockey stick – illustrating the exponential heating of the Earth over the last century compared with the previous millennium. A few years later, Al Gore used that graph in his narration of the climate change documentary, “An Inconvenient Truth.” 

Dr. Mann also began receiving death threats. Congressional leaders accused him of fraudulent research practices. In 2012, the Competitive Enterprise Institute, a libertarian think tank, published a blog post comparing the investigation into Dr. Mann’s work to the investigation into former football coach Jerry Sandusky, who was convicted of sexually abusing children. (Dr. Mann sued the bloggers for defamation. This year he won a judgment of $1 million.)

Climate change skeptics, occasionally funded by fossil fuel interests, began focusing their ire on other scientists as well. “I remember when I first started getting attacked and people started putting down lawsuits and [Freedom of Information Act] requests and insulting me in public,” Dr. Schmidt says. “That was a big shock.” 

In 2011, a group of climate-conscious entrepreneurs, legal scholars, and scientists decided to fight back, creating the Climate Science Legal Defense Fund to protect climate scientists from threats and censorship.

Today, that group is busier than ever, says Lauren Kurtz, its executive director. Her team of lawyers is defending scientists who say they have faced governmental backlash for their research, or who have been disciplined by academic departments for speaking publicly about what they see as the harms of climate change. Sometimes, online abuse of climate scientists has expanded into real-world intimidation, says Ms. Kurtz, who has passed along information to police departments.

It is in this world that Dr. Brown wrote his article.

“On a fundamental level, some amount of skepticism is appropriate, wanted, in science,” she says. “You want scientists to look at each other’s research and try to pull it apart; you want people to double-check and triple-check it, re-create it. ... At the same time, I think that approach has been weaponized by people who want to dispute the scientific reality of climate change, sometimes from a very disingenuous perspective.”

From honest critique to hoax

This is where it gets tricky. Because what’s disingenuous to one person can be an honest critique to another. And the newest wave of climate disinformation has helped undermine the trust needed to decipher between the two. 

A decade ago, the primary claim by climate skeptics was that the Earth is not actually warming. Some still take this line. For instance, a documentary released this spring called “Climate: The Movie” calls global warming a hoax. 

Yet for the most part, the denialist arguments have shifted. In January, the Center for Countering Digital Hate published a report on what it described as a movement from “Old Denial” to “New Denial.” After analyzing thousands of hours of social media content, for example, researchers found that 70% of denial material on YouTube focused either on attacking climate solutions as unworkable, or on attacking the integrity of climate scientists and their research.

“People who want to stop action on climate change have changed their strategy from denying that climate change is real or man-made, to saying that it is real but there is no hope, that the solutions don’t work or the scientists themselves don’t really understand it. None of which is true,” says the group’s CEO, Imran Ahmed. “It shows their cynicism, in that they’ve pivoted so easily from claiming that climate change is fake to, ‘Climate change is real, but there’s no way to fix it,’” he says.

Many researchers say this sort of denialism has been effective. Nearly 80% of Americans say they trust medical scientists, and around 75% say the same for scientists in general, according to the Pew Research Center. But only a third of Americans think climate scientists understand “very well” whether climate change is happening. Only a quarter say climate scientists really understand the effects of climate change on extreme weather events, or know what we should do about it.

“We’re crashing on the rocks of disinformation,” says Brenda Ekwurzel, climate scientist at the Union of Concerned Scientists.

But the notion of “disinformation,” like any idea, can be debatable. Dr. Pielke, for example, is listed on the Skeptical Science website as a spreader of disinformation. Except, he says, he’s not. His career is entirely within “the establishment,” he says.

Dr. Pielke began his career as “one of the many nerds” at the National Center for Atmospheric Research before joining the faculty at the University of Colorado in 2001. His Ph.D. dissertation explored the importance of climate science in public policy. In the early 2000s, he wrote papers urging a broader description of climate change, more in line with that proposed by the United Nations’ Intergovernmental Panel on Climate Change (IPCC), which still cites his work, to enable effective government responses. He votes Democratic and says he has deep concerns about the way humans are changing the Earth’s energy balance.

But Dr. Pielke argues that many of the widely cited cost estimates connecting weather disasters to climate change are mistaken. (Climate advocates regularly assert that climate change is costing the U.S. billions of dollars every year.) His research, he says, shows that extreme weather appears costlier because properties are more valuable. In other words, wealth increase is the real story. He regularly takes issue with media portrayals of extreme weather, and with what he sees as a knee-jerk reaction that connects every wildfire, flood, or hurricane to climate change. The reality is more complex, he says.

He also argues against some of the ways scientists estimate the future impacts of climate change, saying they are unrealistic and extreme. All of this puts him in the “climate change isn’t so bad” misinformation category, according to some groups.

“All you have to do is increase the uncertainty, make these claims, and you delay action,” says Dr. Ekwurzel of the Union of Concerned Scientists. 

But to Dr. Pielke, it just makes him a scientist. He stands by his research and has faced his own sort of harassment. A congressional investigation probed whether his work was secretly funded by fossil fuel interests. (The investigation cleared him of this charge.)

“I’m still establishment,” he says. “I’m one of the few people in the world whose peer-reviewed research is in three working groups of the IPCC. I didn’t leave the mainstream. The mainstream left me.”

“The best way of gaining trust is to be trustworthy”

Most people within the climate field agree that the dynamics of science have shifted in recent years. An increasing number of younger people have come into the field to “make a difference.” Older scientists, meanwhile, worry that their inability to effectively communicate the seriousness of their findings was partly why policymakers have not taken dramatic action on climate change.

Both of these factors compelled more scientists to engage in advocacy. But this hasn’t necessarily been advocacy in a purely political sense. Most of the scientists interviewed for this article view the Earth’s warming with great alarm. They and others are simply trying to get across the urgency of their work.

Yet political leanings do come through. Scientists, along with most academics, are more politically liberal than the country as a whole, according to recent studies about political donations. And this, some researchers say, has helped undermine trust in science among those who lean Republican.

Matthew Burgess, a self-proclaimed “moderate Canadian” and assistant professor at the University of Colorado Boulder, says the politics he noticed within academia prompted him to study polarization around climate change – and to look for common ground.

“It felt like the conversations in the hallways were about how we need to change all of society over decades. But the only ones who were trusted or who could do anything about it were the left-most third of the Democratic Party,” he says. “That’s a dumb theory of change.”

He decided to do outreach on college campuses about polarized climate discussions. He says he spoke with conservatives and progressives and everyone in between, finding eager audiences among each and a willingness to be open – that is, to trust.

“Scientists sometimes overcomplicate the problem of being trusted,” he says. “The best way of gaining trust is to be trustworthy.”

That means acknowledging the downsides of climate action, he says. It means acknowledging where scientific expertise ends and personal, subjective opinion begins. It means acknowledging the big, ethical questions that come along with it. For instance, is it fair to prevent lower-income countries from developing the same fossil fuel-based energy systems that helped make the U.S. and Europe rich?

It also means keeping partisanship and incivility off social media. “The worst thing to happen to climate scientists on Twitter was climate scientists on Twitter,” he says.

And it means better explaining how science actually works.

Science, many in the field point out, is an evolving body of knowledge. There are some physical findings that move toward fact – such as the world is getting warmer, and humans are a cause. Other assumptions  continue to change as researchers gather more information.

“Science is not ‘yes or no’ because science is constantly evolving,” says Dr. Caldas of the Union of Concerned Scientists. Take the pandemic, she says. “One of the best examples that we have of this is COVID, and how much the recommendations changed. ... ‘You don’t need to wear a mask.’ ‘You need to wear a mask.’ ‘There are N95s, and you need to wear those.’ ‘You need to do this.’ ‘You need to do that.’ It kept changing. Why? Because knowledge kept evolving.”

In the case of the Earth’s energy systems, evolving knowledge includes all sorts of scenarios about what will happen in the future. Scientists use complex computerized models, with billions of data points, to evaluate everything from ocean currents to the carbon sequestration within soil to the ripple-down impact of cleaner air or melting glaciers. They then make predictions about future climate impacts.

Much of the modeling has proved to be highly accurate. But there are still uncertainties when it comes to future projections.

“What can you predict with 100% accuracy?” asks Dr. Houlton, the Cornell dean. “The bar that is being placed on climate science is a bar that has been placed on nobody else in society. The future is, by definition, unknown. That can’t be the conversation. I don’t think any climate scientists can say how bad it is going to get.”

As a society, we calculate and act on risk all the time, he and others point out, whether it’s in military preparedness or in car insurance. In climate science, most researchers believe that the more the atmosphere warms, the greater the risk of negative impact. But that’s not a universal opinion. And we as humans are tempted by what we want to hear, including a rosy message that our climate-altered future won’t be so bad after all, and our children and communities will cope just fine.

“The value judgments are tough,” Dr. Houlton says. “I have great colleagues who are ringing alarm bells. I have individuals I respect who say, ‘No, it’s not going to be so bad.’ I get both perspectives.”

The problem, he and others say, is that without trust, the conversation between these two sides can devolve.

“Trust is a foundational attitude,” says Brian Kennedy, a senior researcher at Pew who researched public confidence in various professions and institutions for years. That’s why he and others study it, he explains.

Indeed, says Dr. Brown at The Breakthrough Institute, trust was the purpose of his controversial critique of his own research.

“After saying what I said, the perception that I got was, ‘You are on the bad side; you are a bad person,’” he says. “That’s unfortunate because I am trying to thread the needle; I am trying to be in the middle and say what I think. ... It’s difficult because people like to be on teams. A lot of people see this as a good-team-versus-bad-team thing, and the goal is to defeat the bad team. We can do better.” 

Editor's note: This article has been updated to more accurately reflect the relationship between the Climate Science Legal Defense Fund and local police departments. 

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