essay about is global climate change caused by humans

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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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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 .

Argumentative Essay Writing

Argumentative Essay About Climate Change

Make Your Case: A Guide to Writing an Argumentative Essay on Climate Change

Published on: Mar 2, 2023

Last updated on: Jan 31, 2024

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With the issue of climate change making headlines, it’s no surprise that this has become one of the most debated topics in recent years. 

But what does it really take to craft an effective argumentative essay about climate change? 

Writing an argumentative essay requires a student to thoroughly research and articulate their own opinion on a specific topic. 

To write such an essay, you will need to be well-informed regarding global warming. By doing so, your arguments may stand firm backed by both evidence and logic. 

In this blog, we will discuss some tips for crafting a factually reliable argumentative essay about climate change!

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What is an Argumentative Essay about Climate Change?

The main focus will be on trying to prove that global warming is caused by human activities. Your goal should be to convince your readers that human activity is causing climate change.

To achieve this, you will need to use a variety of research methods to collect data on the topic. You need to make an argument as to why climate change needs to be taken more seriously. 

Argumentative Essay Outline about Climate Change

An argumentative essay about climate change requires a student to take an opinionated stance on the subject. 

The outline of your paper should include the following sections: 

Argumentative Essay About Climate Change Introduction

The first step is to introduce the topic and provide an overview of the main points you will cover in the essay. 

This should include a brief description of what climate change is. Furthermore, it should include current research on how humans are contributing to global warming.

An example is:

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Thesis Statement For Climate Change Argumentative Essay

The thesis statement should be a clear and concise description of your opinion on the topic. It should be established early in the essay and reiterated throughout.

For example, an argumentative essay about climate change could have a thesis statement such as:

Climate Change Argumentative Essay Conclusion

The conclusion should restate your thesis statement and summarize the main points of the essay. 

It should also provide a call to action, encouraging readers to take steps toward addressing climate change. 

For example, 

How To Write An Argumentative Essay On Climate Change 

Writing an argumentative essay about climate change requires a student to take an opinionated stance on the subject. 

Following are the steps to follow for writing an argumentative essay about climate change

Do Your  Research

The first step is researching the topic and collecting evidence to back up your argument. 

You should look at scientific research, articles, and data on climate change as well as current policy solutions. 

Pick A Catchy Title

Once you have gathered your evidence, it is time to pick a title for your essay. It should be specific and concise. 

Outline Your Essay

After selecting a title, create an outline of the main points you will include in the essay. 

This should include an introduction, body paragraphs that provide evidence for your argument, and a conclusion. 

Compose Your Essay

Finally, begin writing your essay. Start with an introduction that provides a brief overview of the main points you will cover and includes your thesis statement. 

Then move on to the body paragraphs, providing evidence to back up your argument. 

Finally, conclude the essay by restating your thesis statement and summarizing the main points. 

Proofread and Revise

Once you have finished writing the essay, it is important to proofread and revise your work. 

Check for any spelling or grammatical errors, and make sure the argument is clear and logical. 

Finally, consider having someone else read over the essay for a fresh perspective. 

By following these steps, you can create an effective argumentative essay on climate change. Good luck! 

Examples Of Argumentative Essays About Climate Change 

Climate Change is real and happening right now. It is one of the most urgent environmental issues that we face today. 

Argumentative essays about this topic can help raise awareness that we need to protect our planet. 

Below you will find some examples of argumentative essays on climate change written by CollegeEssay.org’s expert essay writers.

Argumentative Essay About Climate Change And Global Warming

Persuasive Essay About Climate Change

Argumentative Essay About Climate Change In The Philippines

Argumentative Essay About Climate Change Caused By Humans

Geography Argumentative Essay About Climate Change

Check our extensive blog on argumentative essay examples to ace your next essay!

Good Argumentative Essay Topics About Climate Change 

Choosing a great topic is essential to help your readers understand and engage with the issue.

Here are some suggestions: 

• Should governments fund projects that will reduce the effects of climate change? 
• Is it too late to stop global warming and climate change? 
• Are international treaties effective in reducing carbon dioxide emissions? 
• What are the economic implications of climate change? 
• Should renewable energy be mandated as a priority over traditional fossil fuels? 
• How can individuals help reduce their carbon footprint and fight climate change? 
• Are regulations on industry enough to reduce global warming and climate change? 
• Could geoengineering be used to mitigate climate change? 
• What are the social and political effects of global warming and climate change? 
• Should companies be held accountable for their contribution to climate change? 

Check our comprehensive blog on argumentative essay topics to get more topic ideas!

We hope these topics and resources help you write a great argumentative essay about climate change. 

Now that you know how to write an argumentative essay about climate change, it’s time to put your skills to the test.

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Frequently Asked Questions

What is a good introduction to climate change.

An introduction to a climate change essay can include a short description of why the topic is important and/or relevant. 

It can also provide an overview of what will be discussed in the body of the essay. 

The introduction should conclude with a clear, focused thesis statement that outlines the main argument in your essay. 

What is a good thesis statement for climate change?

A good thesis statement for a climate change essay should state the main point or argument you will make in your essay. 

You could argue that “The science behind climate change is irrefutable and must be addressed by governments, businesses, and individuals.”

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Analysis: Why scientists think 100% of global warming is due to humans

Zeke Hausfather

The extent of the human contribution to modern global warming is a hotly debated topic in political circles, particularly in the US.

During a recent congressional hearing, Rick Perry, the US energy secretary, remarked that “to stand up and say that 100% of global warming is because of human activity, I think on its face, is just indefensible”.

However, the science on the human contribution to modern warming is quite clear. Humans emissions and activities have caused around 100% of the warming observed since 1950, according to the Intergovernmental Panel on Climate Change’s (IPCC) fifth assessment report .

Here Carbon Brief examines how each of the major factors affecting the Earth’s climate would influence temperatures in isolation – and how their combined effects almost perfectly predict long-term changes in the global temperature.

Carbon Brief’s analysis finds that:

• Since 1850, almost all the long-term warming can be explained by greenhouse gas emissions and other human activities.
• If greenhouse gas emissions alone were warming the planet, we would expect to see about a third more warming than has actually occurred. They are offset by cooling from human-produced atmospheric aerosols.
• Aerosols are projected to decline significantly by 2100 , bringing total warming from all factors closer to warming from greenhouse gases alone.
• Natural variability in the Earth’s climate is unlikely to play a major role in long-term warming.

How much warming is caused by humans?

In its 2013 fifth assessment report, the IPCC stated in its summary for policymakers that it is “extremely likely that more than half of the observed increase in global average surface temperature” from 1951 to 2010 was caused by human activity. By “extremely likely”, it meant that there was between a 95% and 100% probability that more than half of modern warming was due to humans.

This somewhat convoluted statement has been often misinterpreted as implying that the human responsibility for modern warming lies somewhere between 50% and 100%. In fact, as NASA’s Dr Gavin Schmidt has pointed out, the IPCC’s implied best guess was that humans were responsible for around 110% of observed warming (ranging from 72% to 146%), with natural factors in isolation leading to a slight cooling over the past 50 years.

Similarly, the recent US fourth national climate assessment found that between 93% to 123% of observed 1951-2010 warming was due to human activities.

These conclusions have led to some confusion as to how more than 100% of observed warming could be attributable to human activity. A human contribution of greater than 100% is possible because natural climate change associated with volcanoes and solar activity would most likely have resulted in a slight cooling over the past 50 years, offsetting some of the warming associated with human activities.

‘Forcings’ that change the climate

Scientists measure the various factors that affect the amount of energy that reaches and remains in the Earth’s climate. They are known as “radiative forcings”.

These forcings include greenhouse gases, which trap outgoing heat, aerosols – both from human activities and volcanic eruptions – that reflect incoming sunlight and influence cloud formation, changes in solar output, changes in the reflectivity of the Earth’s surface associated with land use, and many other factors.

To assess the role of each different forcing in observed temperature changes, Carbon Brief adapted a simple statistical climate model developed by Dr Karsten Haustein and his colleagues at the University of Oxford and University of Leeds . This model finds the relationship between both human and natural climate forcings and temperature that best matches observed temperatures, both globally and over land areas only.

The figure below shows the estimated role of each different climate forcing in changing global surface temperatures since records began in 1850 – including greenhouse gases (red line), aerosols (dark blue), land use (light blue), ozone (pink), solar (yellow) and volcanoes (orange).

The black dots show observed temperatures from the Berkeley Earth surface temperature project, while the grey line shows the estimated warming from the combination of all the different types of forcings.

The combination of all radiative forcings generally matches longer-term changes in observed temperatures quite well. There is some year-to-year variability, primarily from El Niño events , that is not driven by changes in forcings. There are also periods from 1900-1920 and 1930-1950 where some larger disagreements are evident between projected and observed warming, both in this simple model and in more complex climate models .

The chart highlights that, of all the radiative forcings analysed, only increases in greenhouse gas emissions produce the magnitude of warming experienced over the past 150 years.

If greenhouse gas emissions alone were warming the planet, we would expect to see about a third more warming than has actually occurred.

So, what roles do all the other factors play?

• Q&A: How do climate models work?
• Interactive: The impacts of climate change at 1.5C, 2C and beyond
• Explainer: How scientists estimate ‘climate sensitivity’
• Mapped: How every part of the world has warmed – and could continue to warm

The extra warming from greenhouse gases is being offset by sulphur dioxide and other products of fossil fuel combustion that form atmospheric aerosols . Aerosols in the atmosphere both reflect incoming solar radiation back into space and increase the formation of high, reflective clouds, cooling the Earth.

Ozone is a short-lived greenhouse gas that traps outgoing heat and warms the Earth. Ozone is not emitted directly, but is formed when methane, carbon monoxide, nitrogen oxides and volatile organic compounds break down in the atmosphere. Increases in ozone are directly attributable to human emissions of these gases.

In the upper atmosphere, reductions in ozone associated with chlorofluorocarbons (CFCs) and other halocarbons depleting the ozone layer have had a modest cooling effect. The net effects of combined lower and upper atmospheric ozone changes have modestly warmed the Earth by a few tenths of a degree.

Changes in the way land is used alter the reflectivity of the Earth’s surface. For example, replacing a forest with a field will generally increase the amount of sunlight reflected back into space, particularly in snowy regions. The net climate effect of land-use changes since 1850 is a modest cooling.

Volcanoes have a short-term cooling effect on the climate due to their injection of sulphate aerosols high into the stratosphere, where they can remain aloft for a few years, reflecting incoming sunlight back into space. However, once the sulphates drift back down to the surface, the cooling effect of volcanoes goes away. The orange line shows the estimated impact of volcanoes on the climate, with large downward spikes in temperatures of up to 0.4C associated with major eruptions.

Finally, solar activity is measured by satellites over the past few decades and estimated based on sunspot counts in the more distant past. The amount of energy reaching the Earth from the sun fluctuates modestly on a cycle of around 11 years. There has been a slight increase in overall solar activity since the 1850s, but the amount of additional solar energy reaching the Earth is small compared to other radiative forcings examined.

Over the past 50 years, solar energy reaching the Earth has actually declined slightly , while temperatures have increased dramatically.

Human forcings match observed warming

The accuracy of this model depends on the accuracy of the radiative forcing estimates. Some types of radiative forcing like that from atmospheric CO2 concentrations can be directly measured and have relatively small uncertainties. Others, such as aerosols, are subject to much greater uncertainties due to the difficulty of accurately measuring their effects on cloud formation.

These are accounted for in the figure below, which shows combined natural forcings (blue line) and human forcings (red line) and the uncertainties that the statistical model associates with each. These shaded areas are based on 200 different estimates of radiative forcings, incorporating research attempting to estimate a range of values for each. Uncertainties in human factors increase after 1960, driven largely by increases in aerosol emissions after that point.

Overall, warming associated with all human forcings agrees quite well with observed warming, showing that about 104% of the total since the start of the “modern” period in 1950 comes from human activities (and 103% since 1850), which is similar to the value reported by the IPCC. Combined natural forcings show a modest cooling, primarily driven by volcanic eruptions.

The simple statistical model used for this analysis by Carbon Brief differs from much more complex climate models generally used by scientists to assess the human fingerprint on warming. Climate models do not simply “fit” forcings to observed temperatures. Climate models also include variations in temperature over space and time, and can account for different efficacies of radiative forcings in different regions of the Earth.

However, when analysing the impact of different forcings on global temperatures, complex climate models generally find results similar to simple statistical models. The figure below, from the IPCC’s Fifth Assessment Report, shows the influence of different factors on temperature for the period from 1950 to 2010. Observed temperatures are shown in black, while the sum of human forcings is shown in orange.

This suggests that human forcings alone would have resulted in approximately 110% of observed warming . The IPCC also included the estimated magnitude of internal variability over that period in the models, which they suggest is relatively small and comparable to that of natural forcings.

As Prof Gabi Hegerl at the University of Edinburgh tells Carbon Brief: “The IPCC report has an estimate that basically says the best guess is no contribution [from natural variability] with not that much uncertainty.”

Land areas are warming faster

Land temperatures have warmed considerably faster than average global temperatures over the past century, with temperatures reaching around 1.7C above pre-industrial levels in recent years. The land temperature record also goes back further in time than the global temperature record, though the period prior to 1850 is subject to much greater uncertainties .

Both human and natural radiative forcings can be matched to land temperatures using the statistical model. The magnitude of human and natural forcings will differ a bit between land and global temperatures. For example, volcanic eruptions appear to have a larger influence on land, as land temperatures are likely to respond faster to rapid changes in forcings.

The figure below shows the relative contribution of each different radiative forcing to land temperatures since 1750.

The combination of all forcings generally matches observed temperatures quite well, with short-term variability around the grey line primarily driven by El Niño and La Niña events. There is a wider variation in temperatures prior to 1850, reflecting the much larger uncertainties in the observational records that far back.

There is still a period around 1930 and 1940 where observations exceed what the model predicts, though the differences are less pronounced than in global temperatures and the 1900-1920 divergence is mostly absent in land records.

Volcanic eruptions in the late 1700s and early 1800s stand out sharply in the land record. The eruption of Mount Tambora in Indonesia in 1815 may have cooled land temperatures by a massive 1.5C, though records at the time were limited to parts of the Northern Hemisphere and it is, therefore, hard to draw a firm conclusion about global impacts. In general, volcanoes appear to cool land temperatures by nearly twice as much as global temperatures.

What may happen in the future?

Carbon Brief used the same model to project future temperature changes associated with each forcing factor. The figure below shows observations up to 2017, along with future post-2017 radiative forcings from RCP6.0 , a medium-to-high future warming scenario.

When provided with the radiative forcings for the RCP6.0 scenario, the simple statistical model shows warming of around 3C by 2100, nearly identical to the average warming that climate models find.

Future radiative forcing from CO2 is expected to continue to increase if emissions rise. Aerosols, on the other hand, are projected to peak at today’s levels and decline significantly by 2100 , driven in large part by concerns about air quality. This reduction in aerosols will enhance overall warming, bringing total warming from all radiative forcing closer to warming from greenhouse gases alone. The RCP scenarios assume no specific future volcanic eruptions, as the timing of these is unknowable, while solar output continues its 11-year cycle.

This approach can also be applied to land temperatures, as shown in the figure below. Here, land temperatures are shown between 1750 and 2100, with post-2017 forcings also from RCP6.0.

The land is expected to warm about 30% faster than the globe as a whole, as the rate of warming over the oceans is buffered by ocean heat uptake. This is seen in the model results, where land warms by around 4C by 2100 compared to 3C globally in the RCP6.0 scenario.

There is a wide range of future warming possible from different RCP scenarios and different values for the sensitivity of the climate system , but all show a similar pattern of declining future aerosol emissions and a larger role for greenhouse gas forcing in future temperatures.

The role of natural variability

While natural forcings from solar and volcanoes do not seem to play much of a role in long-term warming, there is also natural variability associated with ocean cycles and variations in ocean heat uptake.

As the vast majority of energy trapped by greenhouse gases is absorbed by the oceans rather than the atmosphere, changes in the rate of ocean heat uptake can potentially have large impacts on the surface temperature. Some researchers have argued that multidecadal cycles, such as the Atlantic Multidecadal Oscillation (AMO) and Pacific Decadal Oscillation (PDO), can play a role in warming at a decadal scale.

While human factors explain all the long-term warming, there are some specific periods that appear to have warmed or cooled faster than can be explained based on our best estimates of radiative forcing. For example, the modest mismatch between the radiative forcing-based estimate and observations during the mid-1900s might be evidence of a role for natural variability during that period.

A number of researchers have examined the potential for natural variability to impact long-term warming trends. They have found that it generally plays a limited role. For example, Dr Markus Huber and Dr Reto Knutti at the Institute for Atmospheric and Climate Science (IAC) in Zurich found a maximum possible contribution of natural variability of around 26% (+/- 12%) over the past 100 years and 18% (+/- 9%) over the past 50 years.

Knutti tells Carbon Brief:

“We can never completely rule out that natural variability is larger than we currently think. But that is a weak argument: you can, of course, never rule out the unknown unknown. The question is whether there is strong, or even any evidence for it. And the answer is no, in my view.

Models get the short-term temperature variability approximately right. In many cases, they even have too much. And for the long term, we can’t be sure because the observations are limited. But the forced response pretty much explains the observations, so there is no evidence from the 20th century that we are missing something…

Even if models were found to underestimate internal variability by a factor of three, it is extremely unlikely [less than 5% chance] that internal variability could produce a trend as large as observed.”

Similarly, Dr Martin Stolpe and colleagues, also at IAC, recently analysed the role of multidecadal natural variability in both the Atlantic and Pacific oceans. They found that “less than 10% of the observed global warming during the second half of the 20th century is caused by internal variability in these two ocean basins, reinforcing the attribution of most of the observed warming to anthropogenic forcings”.

Internal variability is likely to have a much larger role in regional temperatures. For example, in producing unusually warm periods in the Arctic and the US in the 1930s. However, its role in influencing long-term changes in global surface temperatures appears to be limited.

While there are natural factors that affect the Earth’s climate, the combined influence of volcanoes and changes in solar activity would have resulted in cooling rather than warming over the past 50 years.

The global warming witnessed over the past 150 years matches nearly perfectly what is expected from greenhouse gas emissions and other human activity, both in the simple model examined here and in more complex climate models. The best estimate of the human contribution to modern warming is around 100%.

Some uncertainty remains due to the role of natural variability, but researchers suggest that ocean fluctuations and similar factors are unlikely to be the cause of more than a small fraction of modern global warming.

Methodology

The simple statistical model used in this article is adapted from the Global Warming Index published by Haustein et al ( 2017 ). In turn, it is based on the Otto et al ( 2015 ) model.

The model estimates contributions to observed climate change and removes the impact of natural year-to-year fluctuations by a multiple linear regression of observed temperatures and estimated responses to total human-induced and total natural drivers of climate change. The forcing responses are provided by the standard simple climate model given in Chapter 8 of IPCC ( 2013 ), but the size of these responses is estimated by the fit to the observations. The forcings are based on IPCC (2013) values and were updated to 2017 using data from NOAA and ECLIPSE . 200 variations of these forcings were provided by Dr. Piers Forster  of the University of Leeds , reflecting the uncertainty in forcing estimates. An Excel spreadsheet containing their model is also provided.

The model was adapted by calculating forcing responses for each of the different major climate forcings rather than simply total human and natural forcings, using the Berkeley Earth record for observations. The decay time of thermal response used in converting forcings to forcing responses was adjusted to be one year rather than four years for volcanic forcings to better reflect the fast response time present in observations. The effects of El Niño and La Niña (ENSO) events was removed from the observations using an approach adapted from Foster and Rahmstorf ( 2011 ) and the Kaplan El Niño 3.4 index when calculating the volcanic temperature response, as the overlap between volcanoes and ENSO otherwise complicates empirical estimates.

The temperature response for each individual forcing was calculated by scaling their forcing responses by the total human or natural coefficients from the regression model . The regression model was also run separately for land temperatures. Temperature responses for each forcing between 2018 and 2100 were estimated using forcing data from RCP6.0, normalised to match the magnitude of observed forcings at the end of 2017.

Uncertainties in total human and total natural temperature response was estimated using a Monte Carlo analysis of 200 different forcing series, as well as the uncertainties in the estimated regression coefficients. The Python code used to run the model is archived with GitHub and available for download .

Observational data from 2017 shown in the figures is based on the average of the first 10 months of the year and is likely to be quite similar to the ultimate annual value.

• Why scientists think 100% of global warming is due to humans

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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 Causes of Climate Change

Human activities are driving the global warming trend observed since the mid-20th century.

• The greenhouse effect is essential to life on Earth, but human-made emissions in the atmosphere are trapping and slowing heat loss to space.
• Five key greenhouse gases are carbon dioxide, nitrous oxide, methane, chlorofluorocarbons, and water vapor.
• While the Sun has played a role in past climate changes, the evidence shows the current warming cannot be explained by the Sun.

Increasing Greenhouses Gases Are Warming the Planet

Scientists attribute the global warming trend observed since the mid-20 th century to the human expansion of the "greenhouse effect" 1 — warming that results when the atmosphere traps heat radiating from Earth toward space.

Life on Earth depends on energy coming from the Sun. About half the light energy reaching Earth's atmosphere passes through the air and clouds to the surface, where it is absorbed and radiated in the form of infrared heat. About 90% of this heat is then absorbed by greenhouse gases and re-radiated, slowing heat loss to space.

Four Major Gases That Contribute to the Greenhouse Effect

Carbon dioxide.

A vital component of the atmosphere, carbon dioxide (CO 2 ) is released through natural processes (like volcanic eruptions) and through human activities, such as burning fossil fuels and deforestation.

Like many atmospheric gases, methane comes from both natural and human-caused sources. Methane comes from plant-matter breakdown in wetlands and is also released from landfills and rice farming. Livestock animals emit methane from their digestion and manure. Leaks from fossil fuel production and transportation are another major source of methane, and natural gas is 70% to 90% methane.

Nitrous Oxide

A potent greenhouse gas produced by farming practices, nitrous oxide is released during commercial and organic fertilizer production and use. Nitrous oxide also comes from burning fossil fuels and burning vegetation and has increased by 18% in the last 100 years.

Chlorofluorocarbons (CFCs)

These chemical compounds do not exist in nature – they are entirely of industrial origin. They were used as refrigerants, solvents (a substance that dissolves others), and spray can propellants.

FORCING:  Something acting upon Earth's climate that causes a change in how energy flows through it (such as long-lasting, heat-trapping gases - also known as greenhouse gases). These gases slow outgoing heat in the atmosphere and cause the planet to warm.

Another Gas That Contributes to the Greenhouse Effect:

Water vapor.

Water vapor is the most abundant greenhouse gas, but because the warming ocean increases the amount of it in our atmosphere, it is not a direct cause of climate change. Credit:  John Fowler  on  Unsplash

FEEDBACKS:  A process where something is either amplified or reduced as time goes on, such as water vapor increasing as Earth warms leading to even more warming.

Human Activity Is the Cause of Increased Greenhouse Gas Concentrations

Over the last century, burning of fossil fuels like coal and oil has increased the concentration of atmospheric carbon dioxide (CO 2 ). This increase happens because the coal or oil burning process combines carbon with oxygen in the air to make CO 2 . To a lesser extent, clearing of land for agriculture, industry, and other human activities has increased concentrations of greenhouse gases.

The industrial activities that our modern civilization depends upon have raised atmospheric carbon dioxide levels by nearly 50% since 1750 2 . This increase is due to human activities, because scientists can see a distinctive isotopic fingerprint in the atmosphere.

In its Sixth Assessment Report, the Intergovernmental Panel on Climate Change, composed of scientific experts from countries all over the world, concluded that it is unequivocal that the increase of CO 2 , methane, and nitrous oxide in the atmosphere over the industrial era is the result of human activities and that human influence is the principal driver of many changes observed across the atmosphere, ocean, cryosphere and biosphere.

"Since systematic scientific assessments began in the 1970s, the influence of human activity on the warming of the climate system has evolved from theory to established fact."

Intergovernmental Panel on Climate Change

The panel's AR6 Working Group I (WGI) Summary for Policymakers report is online at https://www.ipcc.ch/report/ar6/wg1/ .

Evidence Shows That Current Global Warming Cannot Be Explained by Solar Irradiance

Scientists use a metric called Total Solar Irradiance (TSI) to measure the changes in energy the Earth receives from the Sun. TSI incorporates the 11-year solar cycle and solar flares/storms from the Sun's surface.

Studies show that solar variability has played a role in past climate changes. For example, a decrease in solar activity coupled with increased volcanic activity helped trigger the Little Ice Age.

But several lines of evidence show that current global warming cannot be explained by changes in energy from the Sun:

• Since 1750, the average amount of energy from the Sun either remained constant or decreased slightly 3 .
• If a more active Sun caused the warming, scientists would expect warmer temperatures in all layers of the atmosphere. Instead, they have observed a cooling in the upper atmosphere and a warming at the surface and lower parts of the atmosphere. That's because greenhouse gases are slowing heat loss from the lower atmosphere.
• Climate models that include solar irradiance changes can’t reproduce the observed temperature trend over the past century or more without including a rise in greenhouse gases.

1. IPCC 6 th Assessment Report, WG1, Summary for Policy Makers, Sections A, “ The Current State of the Climate ”

IPCC 6 th Assessment Report, WG1, Technical Summary, Sections TS.1.2, TS.2.1 and TS.3.1

2. P. Friedlingstein, et al., 2022: “Global Carbon Budget 2022”, Earth System Science Data ( 11 Nov 2022): 4811–4900. https://doi.org/10.5194/essd-14-4811-2022

3. IPCC 6 th Assessment Report, WG1, Chapter 2, Section 2.2.1, “ Solar and Orbital Forcing ” IPCC 6 th Assessment Report, WG1, Chapter 7, Sections 7.3.4.4, 7.3.5.2, Figure 7.6, “ Solar ” M. Lockwood and W.T. Ball, Placing limits on long-term variations in quiet-Sun irradiance and their contribution to total solar irradiance and solar radiative forcing of climate,” Proceedings of the Royal Society A , 476, issue 2228 (24 June 2020): https://doi 10.1098/rspa.2020.0077

Header image credit: Pixabay/stevepb Four Major Gases image credit: Adobe Stock/Ilya Glovatskiy

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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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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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What Is Climate Change?

Climate change is a long-term change in the average weather patterns that have come to define Earth’s local, regional and global climates. These changes have a broad range of observed effects that are synonymous with the term.

Changes observed in Earth’s climate since the mid-20th century are driven by human activities, particularly fossil fuel burning, which increases heat-trapping greenhouse gas levels in Earth’s atmosphere, raising Earth’s average surface temperature. Natural processes, which have been overwhelmed by human activities, can also contribute to climate change, including internal variability (e.g., cyclical ocean patterns like El Niño, La Niña and the Pacific Decadal Oscillation) and external forcings (e.g., volcanic activity, changes in the Sun’s energy output , variations in Earth’s orbit ).

Scientists use observations from the ground, air, and space, along with computer models , to monitor and study past, present, and future climate change. Climate data records provide evidence of climate change key indicators, such as global land and ocean temperature increases; rising sea levels; ice loss at Earth’s poles and in mountain glaciers; frequency and severity changes in extreme weather such as hurricanes, heatwaves, wildfires, droughts, floods, and precipitation; and cloud and vegetation cover changes.

“Climate change” and “global warming” are often used interchangeably but have distinct meanings. Similarly, the terms "weather" and "climate" are sometimes confused, though they refer to events with broadly different spatial- and timescales.

What Is Global Warming?

Global warming is the long-term heating of Earth’s surface observed since the pre-industrial period (between 1850 and 1900) due to human activities, primarily fossil fuel burning, which increases heat-trapping greenhouse gas levels in Earth’s atmosphere. This term is not interchangeable with the term "climate change."

Since the pre-industrial period, human activities are estimated to have increased Earth’s global average temperature by about 1 degree Celsius (1.8 degrees Fahrenheit), a number that is currently increasing by more than 0.2 degrees Celsius (0.36 degrees Fahrenheit) per decade. The current warming trend is unequivocally the result of human activity since the 1950s and is proceeding at an unprecedented rate over millennia.

Weather vs. Climate

“If you don’t like the weather in New England, just wait a few minutes.” - Mark Twain

Weather refers to atmospheric conditions that occur locally over short periods of time—from minutes to hours or days. Familiar examples include rain, snow, clouds, winds, floods, or thunderstorms.

Climate, on the other hand, refers to the long-term (usually at least 30 years) regional or even global average of temperature, humidity, and rainfall patterns over seasons, years, or decades.

Find Out More: A Guide to NASA’s Global Climate Change Website

This website provides a high-level overview of some of the known causes, effects and indications of global climate change:

Evidence. Brief descriptions of some of the key scientific observations that our planet is undergoing abrupt climate change.

Causes. A concise discussion of the primary climate change causes on our planet.

Effects. A look at some of the likely future effects of climate change, including U.S. regional effects.

Vital Signs. Graphs and animated time series showing real-time climate change data, including atmospheric carbon dioxide, global temperature, sea ice extent, and ice sheet volume.

Earth Minute. This fun video series explains various Earth science topics, including some climate change topics.

Other NASA Resources

Goddard Scientific Visualization Studio. An extensive collection of animated climate change and Earth science visualizations.

Sea Level Change Portal. NASA's portal for an in-depth look at the science behind sea level change.

NASA’s Earth Observatory. Satellite imagery, feature articles and scientific information about our home planet, with a focus on Earth’s climate and environmental change.

Header image is of Apusiaajik Glacier, and was taken near Kulusuk, Greenland, on Aug. 26, 2018, during NASA's Oceans Melting Greenland (OMG) field operations. Learn more here . Credit: NASA/JPL-Caltech

Science News

Abdulhamid Hosbas/Anadolu Agency via Getty Images

Century of Science: Theme

Our climate change crisis

The climate change emergency.

Even in a world increasingly battered by weather extremes, the summer 2021 heat wave in the Pacific Northwest stood out. For several days in late June, cities such as Vancouver, Portland and Seattle baked in record temperatures that killed hundreds of people. On June 29 Lytton, a village in British Columbia, set an all-time heat record for Canada, at 121° Fahrenheit (49.6° Celsius); the next day, the village was incinerated by a wildfire.

Within a week, an international group of scientists had analyzed this extreme heat and concluded it would have been virtually impossible without climate change caused by humans. The planet’s average surface temperature has risen by at least 1.1 degree Celsius since preindustrial levels of 1850–1900 — because people are loading the atmosphere with heat-trapping gases produced during the burning of fossil fuels, such as coal and gas, and from cutting down forests.

A little over 1 degree of warming may not sound like a lot. But it has already been enough to fundamentally transform how energy flows around the planet. The pace of change is accelerating, and the consequences are everywhere. Ice sheets in Greenland and Antarctica are melting, raising sea levels and flooding low-lying island nations and coastal cities. Drought is parching farmlands and the rivers that feed them. Wildfires are raging. Rains are becoming more intense, and weather patterns are shifting .

The roots of understanding this climate emergency trace back more than a century and a half. But it wasn’t until the 1950s that scientists began the detailed measurements of atmospheric carbon dioxide that would prove how much carbon is pouring from human activities. Beginning in the 1960s, researchers began developing comprehensive computer models that now illuminate the severity of the changes ahead.

Global average temperature change, 1850–2021

Long-term climate datasets show that Earth’s average surface temperature (combined land and ocean) has increased by more than 1 degree Celsius since preindustrial times. Temperature change is the difference from the 1850–1900 average.

Today we know that climate change and its consequences are real, and we are responsible. The emissions that people have been putting into the air for centuries — the emissions that made long-distance travel, economic growth and our material lives possible — have put us squarely on a warming trajectory . Only drastic cuts in carbon emissions, backed by collective global will, can make a significant difference.

“What’s happening to the planet is not routine,” says Ralph Keeling, a geochemist at the Scripps Institution of Oceanography in La Jolla, Calif. “We’re in a planetary crisis.” — Alexandra Witze

Tracking a Greenland glacier

The calving front of Greenland’s Helheim Glacier, which flows toward the sea where it crumbles into icebergs, held roughly the same position from the 1970s until 2001 (left, the calving front is to the far right of the image). But by 2005 (right), it had retreated 7.5 kilometers toward its source. 

The first climate scientists

One day in the 1850s, Eunice Newton Foote, an amateur scientist and women’s rights activist living in upstate New York, put two glass jars in sunlight. One contained regular air — a mix of nitrogen, oxygen and other gases including carbon dioxide — while the other contained just CO 2 . Both had thermometers in them. As the sun’s rays beat down, Foote observed that the jar of CO 2 alone heated more quickly, and was slower to cool, than the one containing plain air.

The results prompted Foote to muse on the relationship between CO 2 , the planet and heat. “An atmosphere of that gas would give to our earth a high temperature,” she wrote in an 1856 paper summarizing her findings .

Three years later, working independently and apparently unaware of Foote’s discovery, Irish physicist John Tyndall showed the same basic idea in more detail. With a set of pipes and devices to study the transmission of heat, he found that CO 2 gas, as well as water vapor, absorbed more heat than air alone. He argued that such gases would trap heat in Earth’s atmosphere, much as panes of glass trap heat in a greenhouse, and thus modulate climate. “As a dam built across a river causes a local deepening of the stream, so our atmosphere, thrown as a barrier across the terrestrial rays, produces a local heightening of the temperature at the Earth’s surface,” he wrote in 1862.

Today Tyndall is widely credited with the discovery of how what are now called greenhouse gases heat the planet, earning him a prominent place in the history of climate science. Foote faded into relative obscurity — partly because of her gender, partly because her measurements were less sensitive. Yet their findings helped kick off broader scientific exploration of how the composition of gases in Earth’s atmosphere affects global temperatures.

Carbon floods in

Humans began substantially affecting the atmosphere around the turn of the 19th century, when the Industrial Revolution took off in Britain. Factories burned tons of coal; fueled by fossil fuels, the steam engine revolutionized transportation and other industries. In the decades since, fossil fuels including oil and natural gas have been harnessed to drive a global economy. All these activities belch gases into the air.

Yet Svante Arrhenius, a Swedish physical chemist, wasn’t worried about the Industrial Revolution when he began thinking in the late 1800s about changes in atmospheric CO 2 levels. He was instead curious about ice ages — including whether a decrease in volcanic eruptions, which can put CO 2 into the atmosphere, would lead to a future ice age. Bored and lonely in the wake of a divorce, Arrhenius set himself to months of laborious calculations involving moisture and heat transport in the atmosphere at different zones of latitude. In 1896 he reported that halving the amount of CO 2 in the atmosphere could indeed bring about an ice age — and that doubling CO 2 would raise global temperatures by around 5 to 6 degrees C.

It was a remarkably prescient finding for work that, out of necessity, had simplified Earth’s complex climate system down to just a few variables. Today, estimates for how much the planet will warm through a doubling of CO 2 — a measure known as climate sensitivity — range between 1.5 degrees and 4.5 degrees Celsius. (The range remains broad in part because scientists now incorporate their understanding of many more planetary feedbacks than were recognized in Arrhenius’ day.)  

But Arrhenius’ findings didn’t gain much traction with other scientists at the time. The climate system seemed too large, complex and inert to change in any meaningful way on a timescale that would be relevant to human society. Geologic evidence showed, for instance, that ice ages took thousands of years to start and end. What was there to worry about? And other laboratory experiments — later shown to be flawed — appeared to indicate that changing levels of CO 2 would have little impact on heat absorption in the atmosphere. Most scientists aware of the work came to believe that Arrhenius had been proved wrong.

One researcher, though, thought the idea was worth pursuing. Guy Stewart Callendar, a British engineer and amateur meteorologist, had tallied weather records over time, obsessively enough to determine that average temperatures were increasing at 147 weather stations around the globe. In 1938, in a paper in a Royal Meteorological Society journal , he linked this temperature rise to the burning of fossil fuels. Callendar estimated that fossil fuel burning had put around 150 billion metric tons of CO 2 into the atmosphere since the late 19th century.

Like many of his day, Callendar didn’t see global warming as a problem. Extra CO 2 would surely stimulate plants to grow and allow crops to be farmed in new regions. “In any case the return of the deadly glaciers should be delayed indefinitely,” he wrote. But his work revived discussions tracing back to Tyndall and Arrhenius about how the planetary system responds to changing levels of gases in the atmosphere. And it began steering the conversation toward how human activities might drive those changes.

When World War II broke out the following year, the global conflict redrew the landscape for scientific research. Hugely important wartime technologies, such as radar and the atomic bomb, set the stage for “big science” studies that brought nations together to tackle high-stakes questions of global reach. And that allowed modern climate science to emerge.

The Keeling curve and climate change

One major postwar effort was the International Geophysical Year, an 18-month push in 1957–1958 that involved a wide array of scientific field campaigns including exploration in the Arctic and Antarctica. Climate change wasn’t a high research priority during the IGY, but some scientists in California, led by Roger Revelle of the Scripps Institution of Oceanography in La Jolla, used the funding influx to begin a project they’d long wanted to do. The goal was to measure CO 2 levels at different locations around the world, accurately and consistently.

The job fell to geochemist Charles David Keeling, who put ultraprecise CO 2 monitors in Antarctica and on the Hawaiian volcano of Mauna Loa. Funds soon ran out to maintain the Antarctic record, but the Mauna Loa measurements continued. Thus was born one of the most iconic datasets in all of science — the “Keeling curve,” which tracks the rise of atmospheric CO 2 . When Keeling began his measurements in 1958, CO 2 made up 315 parts per million of the global atmosphere. Within just a few years it became clear that the number was increasing year by year. Because plants take up CO 2 as they grow in spring and summer and release it as they decompose in fall and winter, CO 2 concentrations rose and fell each year in a sawtooth pattern — but superimposed on that pattern was a steady march upward.  

Monthly average CO 2 concentrations at Mauna Loa Observatory

Atmospheric carbon dioxide measurements collected continuously since 1958 at Mauna Loa volcano in Hawaii show the rise due to human activities. The visible sawtooth pattern is due to seasonal plant growth: Plants take up CO 2 in the growing seasons, then release it as they decompose in fall and winter.

“The graph got flashed all over the place — it was just such a striking image,” says Ralph Keeling, who is Charles David Keeling’s son. Over the years, as the curve marched higher, “it had a really important role historically in waking people up to the problem of climate change.” The Keeling curve has been featured in countless earth science textbooks, congressional hearings and in Al Gore’s 2006 documentary on climate change, An Inconvenient Truth . Each year the curve keeps going up: In 2016 it passed 400 ppm of CO 2 in the atmosphere, as measured during its typical annual minimum in September. In 2021, the annual minimum was 413 ppm. (Before the Industrial Revolution, CO 2 levels in the atmosphere had been stable for centuries at around 280 ppm.)

Around the time that Keeling’s measurements were kicking off, Revelle also helped develop an important argument that the CO 2 from human activities was building up in Earth’s atmosphere. In 1957 he and Hans Suess, also at Scripps at the time, published a paper that traced the flow of radioactive carbon through the oceans and the atmosphere. They showed that the oceans were not capable of taking up as much CO 2 as previously thought; the implication was that much of the gas must be going into the atmosphere instead. “Human beings are now carrying out a large-scale geophysical experiment of a kind that could not have happened in the past nor be reproduced in the future,” Revelle and Suess wrote in the paper. It’s one of the most famous sentences in earth science history.

“Human beings are now carrying out a large-scale geophysical experiment of a kind that could not have happened in the past nor be reproduced in the future.”

Here was the insight underlying modern climate science: Atmosheric CO 2 is increasing, and humans are causing the buildup. Revelle and Suess became the final piece in a puzzle dating back to Svante Arrhenius and John Tyndall.

“I tell my students that to understand the basics of climate change, you need to have the cutting-edge science of the 1860s, the cutting-edge math of the 1890s and the cutting-edge chemistry of the 1950s,” says Joshua Howe, an environmental historian at Reed College in Portland, Ore.

Environmental awareness grows

As this scientific picture began to emerge in the late 1950s, Science News was on the story. A March 1, 1958 article in Science News Letter , “Weather May Be Warming,” described a warm winter month in the Northern Hemisphere. It posits three theories, including that “carbon dioxide poured into the atmosphere by a booming industrial civilization could have caused the increase. By burning up about 100 billion tons of coal and oil since 1900, man himself may be changing the climate.” By 1972, the magazine was reporting on efforts to expand global atmospheric greenhouse gas monitoring beyond Keeling’s work; two years later, the U.S. National Oceanic and Atmospheric Administration launched its own CO 2 monitoring network, now the biggest in the world.

Environmental awareness on other issues grew in the 1960s and 1970s. Rachel Carson catalyzed the modern U.S. environmental movement in 1962 when she published a magazine series and then a book, Silent Spring , condemning the pesticide DDT for its ecological impacts. 1970 saw the celebration of the first Earth Day , in the United States and elsewhere, and in India in 1973 a group of women led a series of widely publicized protests against deforestation. This Chipko movement explicitly linked environmental protection with protecting human communities, and helped seed other environmental movements.

The fragility of global energy supplies was also becoming more obvious through the 1970s. The United States, heavily dependent on other countries for oil imports, entered a gas shortage in 1973–74 when Arab members of the Organization of the Petroleum Exporting Countries cut off oil supplies because of U.S. government support for Israel. The shortage prompted more people to think about the finiteness of natural resources and the possibility of overtaxing the planet. — Alexandra Witze

Climate change evidence piles up

Observational data collected throughout the second half of the 20th century helped researchers gradually build their understanding of how human activities were transforming the planet. “It was a sort of slow accretion of evidence and concern,” says historian Joshua Howe of Reed College.

Environmental records from the past, such as tree rings and ice cores, established that the current changes in climate are unusual compared with the recent past. Yet such paleoclimatology data also showed that climate has changed quickly in the deep past — driven by triggers other than human activity, but with lessons for how abrupt planetary transformations can be.

Ice cores pulled from ice sheets, such as that atop Greenland, offer some of the most telling insights for understanding past climate change. Each year snow falls atop the ice and compresses into a fresh layer of ice representing climate conditions at the time it formed. The abundance of certain forms, or isotopes, of oxygen and hydrogen in the ice allows scientists to calculate the temperature at which it formed, and air bubbles trapped within the ice reveal how much carbon dioxide and other greenhouse gases were in the atmosphere at that time. So drilling down into an ice sheet is like reading the pages of a history book that go back in time the deeper you go.

Scientists began reading these pages in the early 1960s, using ice cores drilled at a U.S. military base in northwest Greenland . Contrary to expectations that past climates were stable, the cores hinted that abrupt climate shifts had happened over the last 100,000 years. By 1979, an international group of researchers was pulling another deep ice core from a second location in Greenland — and it, too, showed that abrupt climate change had occurred in the past. In the late 1980s and early 1990s a pair of European- and U.S.-led drilling projects retrieved even deeper cores from near the top of the ice sheet, pushing the record of past temperatures back a quarter of a million years.

Together with other sources of information, such as sediment cores drilled from the seafloor and molecules preserved in ancient rocks, the ice cores allowed scientists to reconstruct past temperature changes in extraordinary detail. Many of those changes happened alarmingly fast. For instance, the climate in Greenland warmed abruptly more than 20 times in the last 80,000 years, with the changes occurring in a matter of decades. More recently, a cold spell that set in around 13,000 years ago suddenly came to an end around 11,500 years ago — and temperatures in Greenland rose 10 degrees Celsius in a decade.

Evidence for such dramatic climate shifts laid to rest any lingering ideas that global climate change would be slow and unlikely to occur on a timescale that humans should worry about. “It’s an important reminder of how ‘tippy’ things can be,” says Jessica Tierney, a paleoclimatologist at the University of Arizona in Tucson.

More evidence of global change came from Earth-observing satellites, which brought a new planet-wide perspective on global warming beginning in the 1960s. From their viewpoint in the sky, satellites have measured the steady rise in global sea level — currently 3.4 millimeters per year and accelerating, as warming water expands and as ice sheets melt — as well as the rapid decline in ice left floating on the Arctic Ocean each summer at the end of the melt season. Gravity-sensing satellites have ‘weighed’ the Antarctic and Greenlandic ice sheets from above since 2002, reporting that more than 400 billion metric tons of ice are lost each year.

Temperature observations taken at weather stations around the world also confirm that we are living in the hottest years on record. The 10 warmest years since record keeping began in 1880 have all occurred since 2005. And nine of those 10 have come since 2010.

What’s more, extreme weather is hammering the planet more and more frequently. That 2021 heat wave in the Pacific Northwest, for instance, is just a harbinger of what’s to come. — Alexandra Witze

Worrisome predictions from climate models

By the 1960s, there was no denying that the planet was warming. But understanding the consequences of those changes — including the threat to human health and well-being — would require more than observational data. Looking to the future depended on computer simulations: complex calculations of how energy flows through the planetary system. Such models of the climate system have been crucial to developing projections for what we can expect from greenhouse warming.

A first step in building climate models was to connect everyday observations of weather to the concept of forecasting future climate. During World War I, the British mathematician Lewis Fry Richardson imagined tens of thousands of meteorologists working to forecast the weather, each calculating conditions for a small part of the atmosphere but collectively piecing together a global forecast. Richardson published his work in 1922, to reviews that called the idea “of almost quixotic boldness.”

But it wasn’t until after World War II that computational power turned Richardson’s dream into reality. In the wake of the Allied victory, which relied on accurate weather forecasts for everything from planning D-Day to figuring out when and where to drop the atomic bombs, leading U.S. mathematicians acquired funding from the federal government to improve predictions. In 1950 a team led by Jule Charney, a meteorologist at the Institute for Advanced Study in Princeton, N.J., used the ENIAC, the first general-purpose, programmable electronic computer, to produce the first computer-driven regional weather forecast . The forecasting was slow and rudimentary, but it built on Richardson’s ideas of dividing the atmosphere into squares, or cells, and computing the weather for each of those. With the obscure title “Numerical integration of the barotropic vorticity equation,” the paper reporting the results set the stage for decades of climate modeling to follow.

By 1956 Norman Phillips, a member of Charney’s team, had produced the world’s first general circulation model, which captured how energy flows between the oceans, atmosphere and land. Phillips ran the calculations on a computer with just 5 kilobytes of memory, yet it was able to reproduce monthly and seasonal patterns in the lower atmosphere. That meant scientists could begin developing more realistic models of how the planet responds to factors such as increasing levels of greenhouse gases. The field of climate modeling was born.

The work was basic at first, because early computers simply didn’t have much computational power to simulate all aspects of the planetary system. “People thought that it was stupid to try to study this greenhouse-warming issue by three-dimensional model[s], because it cost so much computer time,” meteorologist Syukuro Manabe told physics historian Spencer Weart in a 1989 oral history .

Climate models have predicted how much ice the Ilulissat region of the Greenland ice sheet might lose by 2300 based on different scenarios for greenhouse gas emissions. The models are compared to 2008 (first image). In a best-case scenario, in which emissions peak by mid-century, the speed at which the glacier is sending ice out into the ocean is much lower (second image) than with a worst-case scenario, in which emissions rise at a high rate (third image).

An important breakthrough came in 1967, when Manabe and Richard Wetherald — both at the Geophysical Fluid Dynamics Laboratory in Princeton, a lab born from Charney’s group — published a paper in the Journal of the Atmospheric Sciences that modeled connections between Earth’s surface and atmosphere and calculated how changes in carbon dioxide would affect the planet’s temperature. Manabe and Wetherald were the first to build a computer model that captured the relevant processes that drive climate , and to accurately simulate how the Earth responds to those processes. (Manabe shared the 2021 Nobel Prize in physics for his work on climate modeling; Wetherald died in 2011.)

The rise of climate modeling allowed scientists to more accurately envision the impacts of global warming. In 1979, Charney and other experts met in Woods Hole, Mass., to try to put together a scientific consensus on what increasing levels of CO 2 would mean for the planet. They analyzed climate models from Manabe and from James Hansen of NASA. The resulting “Charney report” concluded that rising CO 2 in the atmosphere would lead to additional and significant climate change. The ocean might take up much of that heat, the scientists wrote — but “it appears that the warming will eventually occur, and the associated regional climatic changes so important to the assessment of socioeconomic consequence may well be significant.”

In the decades since, climate modeling has gotten increasingly sophisticated . Scientists have drawn up a variety of scenarios for how carbon emissions might change in the future, depending on the stringency of emissions cuts. Modelers use those scenarios to project how climate and weather will change around the globe, from hotter croplands in China to melting glaciers in the Himalayas. Climate simulations have also allowed researchers to identify the fingerprints of human impacts on extreme weather that is already happening, by comparing scenarios that include the influence of human activities with those that do not.

And as climate science firmed up and the most dramatic consequences became clear, the political battles raged. — Alexandra Witze

Climate science meets politics

With the development of climate science tracing back to the early Cold War, perhaps it shouldn’t be a surprise that the science of global warming became enmeshed in broader societal and political battles. A complex stew of political, national and business interests mired society in debates about the reality of climate change, and what to do about it, decades after the science became clear that humans are fundamentally altering the planet’s atmosphere.

Society has pulled itself together before to deal with global environmental problems, such as the Antarctic ozone hole. In 1974 chemists Mario Molina and F. Sherwood Rowland, both of the University of California, Irvine, reported that chlorofluorocarbon chemicals, used in products such as spray cans and refrigerants, caused a chain of reactions that gnawed away at the atmosphere’s protective ozone layer . The resulting ozone hole, which forms over Antarctica every spring, allows more ultraviolet radiation from the sun to make it through Earth’s atmosphere and reach the surface, where it can cause skin cancer and eye damage.

Governments ultimately worked under the auspices of the United Nations to craft the 1987 Montreal Protocol, which strictly limited the manufacture of chlorofluorocarbons . In the years following, the ozone hole began to heal. But fighting climate change would prove to be far more challenging. Chlorofluorocarbons were a suite of chemicals with relatively limited use and for which replacements could be found without too much trouble. But the greenhouse gases that cause global warming stem from a wide variety of human activities, from energy development to deforestation. And transforming entire energy sectors to reduce or eliminate carbon emissions is much more difficult than replacing a set of industrial chemicals.

In 1980, though, researchers took an important step toward banding together to synthesize the scientific understanding of climate change and bring it to the attention of international policy makers. It started at a small scientific conference in Villach, Austria. There, experts met under the auspices of the World Meteorological Organization, the International Council of Scientific Unions and the United Nations Environment Program to discuss the seriousness of climate change. On the train ride home from the meeting, Swedish meteorologist Bert Bolin talked with other participants about how a broader, deeper and more international analysis was needed. In 1985, a second conference was held at Villach to highlight the urgency, and in 1988, the Intergovernmental Panel on Climate Change, the IPCC, was born. Bolin was its first chairperson.

The IPCC became a highly influential and unique body. It performs no original scientific research; instead, it synthesizes and summarizes the vast literature of climate science for policy makers to consider — primarily through massive reports issued every couple of years. The first IPCC report , in 1990, predicted that the planet’s global mean temperature would rise more quickly in the following century than at any point in the last 10,000 years, due to increasing greenhouse gases in the atmosphere. Successive IPCC reports showed more and more confidence in the link between greenhouse emissions and rising global temperatures — and explored how society might mitigate and adapt to coming changes.

IPCC reports have played a key role in providing scientific information for nations discussing how to stabilize greenhouse gas concentrations. This process started with the Rio Earth Summit in 1992 , which resulted in the U.N. Framework Convention on Climate Change. Annual U.N. meetings to tackle climate change led to the first international commitments to reduce emissions, the Kyoto Protocol of 1997. Under it, developed countries committed to reduce emissions of CO 2 and other greenhouse gases. By 2007 the IPCC declared that the reality of climate warming is “unequivocal ”; the group received the Nobel Peace Prize that year along with Al Gore for their work on climate change.

The IPCC process ensured that policy makers had the best science at hand when they came to the table to discuss cutting emissions. “If you go back and look at the original U.N. framework on climate change, already you see the core of the science represented there,” says Rachel Cleetus, a climate policy expert with the Union of Concerned Scientists in Cambridge, Mass. Of course, nations did not have to abide by that science — and they often didn’t.

Throughout the 2000s and 2010s, international climate meetings discussed less hard-core science and more issues of equity. Countries such as China and India pointed out that they needed energy to develop their economies, and that nations responsible for the bulk of emissions through history, such as the United States, needed to lead the way in cutting greenhouse gases. Meanwhile, residents of some of the most vulnerable nations, such as low-lying islands that are threatened by sea level rise, gained visibility and clout at international negotiating forums. “The issues around equity have always been very uniquely challenging in this collective action problem,” says Cleetus.

By 2015, the world’s nations had made some progress on the emissions cuts laid out in the Kyoto Protocol, but it was still not enough to achieve substantial global reductions. That year, a key U.N. climate conference in Paris produced an international agreement to try to limit global warming to 2 degrees C , and preferably 1.5 degrees C, above preindustrial levels.

Every country has its own approach to the challenge of addressing climate change. In the United States, which gets approximately 80 percent of its energy from fossil fuels, sophisticated efforts to downplay and critique the science led to major delays in climate action. For decades U.S. fossil fuel companies such as ExxonMobil worked to influence politicians to take as little action on emissions reductions as possible. Working with a small group of influential scientists, this well-funded, well-orchestrated campaign took many of its tactics from earlier tobacco-industry efforts to cast doubt on the links between smoking and cancer, as historians Naomi Oreskes and Erik Conway documented in their book Merchants of Doubt.

Perhaps the peak of U.S. climate denialism came in the late 1980s and into the 1990s — roughly a century after Swedish physical chemist Svante Arrhenius laid out the consequences of putting too much carbon dioxide into the atmosphere. In 1988 NASA scientist James Hansen testified to lawmakers about the consequences of global warming. “It is already happening now,” Hansen said, summarizing what scientists had long known.

The high-profile nature of Hansen’s testimony, combined with his NASA expertise, vaulted global warming into the public eye in the United States like never before. “It really hit home with a public who could understand that there are reasons that Venus is hot and Mars is cold,” says Joshua Howe, a historian at Reed College. “And that if you use that same reasoning, we have some concerns about what is happening here on Earth.” But Hansen also kicked off a series of bitter public battles about the reality of human-caused climate change that raged for years.        

One common approach of climate skeptics was to attack the environmental data and models that underlie climate science. In 1998, scientist Michael Mann, then at the University of Massachusetts–Amherst, and colleagues published a detailed temperature record that formed the basis of what came to be known as the “hockey stick” graph, so named because the chart showed a sharp rise in temperatures (the hockey blade) at the end of a long, much flatter period (the hockey stick). Skeptics soon demanded the data and software processing tools Mann used to create the graph. Bloggers and self-proclaimed citizen scientists created a cottage industry of questioning new climate science papers under the guise of “audits.” In 2009 hackers broke into a server at the University of East Anglia, a leading climate-research hub in Norwich, England, and released more than 1,000 e-mails between climate scientists. This “Climategate” scandal purported to reveal misconduct on the part of the researchers, but several reviews largely exonerated the scientists.  

The graph that launched climate skeptic attacks

This famous graph, produced by scientist Michael Mann and colleagues, and then reproduced in a 2001 report by the Intergovernmental Panel on Climate Change, dramatically captures temperature change over time. Climate change skeptics made it the center of an all-out attack on climate science.

Such tactics undoubtedly succeeded in feeding politicians’ delay on climate action in the United States, most of it from Republicans. President George W. Bush withdrew the country from the Kyoto Protocol in 2001 ; Donald Trump similarly rejected the Paris accord in 2017 . As late as 2015, the chair of the Senate’s environment committee, James Inhofe of Oklahoma, brought a snowball into Congress on a cold winter’s day in order to continue his argument that human-caused global warming is a “hoax.” In Australia, a similar mix of right-wing denialism and fossil fuel interests has kept climate change commitments in flux, as prime ministers are voted in and out over fierce debates about how the nation should act on climate.

Yet other nations have moved forward. Some European countries such as Germany aggressively pursued renewable energies, such as wind and solar, while activists such as the Swedish teenager Greta Thunberg — the vanguard of a youth-action movement — pressured their governments for more.

In recent years the developing economies of China and India have taken center stage in discussions about climate action. Both nations argue that they must be allowed extra time to wean themselves off fossil fuels in order to continue economic growth. They note that historically speaking, the United States is the largest total emitter of carbon by far.

Total carbon dioxide emissions by country, 1850–2021

These 20 nations have emitted the largest cumulative amounts of carbon dioxide since 1850. Emissions are shown in in billions of metric tons and are broken down into subtotals from fossil fuel use and cement manufacturing (blue) as well as from land use and forestry (green).

China, whose annual CO 2 emissions surpassed those of the United States in 2006, declared several moderate steps in 2021 to reduce emissions, including that it would stop building coal-burning power plants overseas. India announced it would aim for net-zero emissions by 2070, the first time it has set a date for this goal.

Yet such pledges continue to be criticized. At the 2021 U.N. Climate Change Conference in Glasgow, Scotland, India was globally criticized for not committing to a complete phaseout of coal — although the two top emitters, China and the United States, have not themselves committed to phasing out coal. “There is no equity in this,” says Aayushi Awasthy, an energy economist at the University of East Anglia. — Alexandra Witze

Facing a warmer future

Climate change creeps up gradually on society, except when it doesn’t. The slow increase in sea level, for instance, causes waters to lap incrementally higher at shorelines year after year. But when a big storm comes along — which may be happening more frequently due to climate change — the consequences become much more obvious. Storm surge rapidly swamps communities and wreaks disproportionate havoc. That’s why New York City installed floodgates in its subway and tunnel system in the wake of 2012’s Superstorm Sandy , and why the Pacific island nation of Tuvalu has asked Australia and New Zealand to be prepared to take in refugees fleeing from rising sea levels.

The list of climate impacts goes on and on — and in many cases, changes are coming faster than scientists had envisioned a few decades ago. The oceans are becoming more acidic as they absorb carbon dioxide, harming tiny marine organisms that build protective calcium carbonate shells and are the base of the marine food web. Warmer waters are bleaching coral reefs. Higher temperatures are driving animal and plant species into areas in which they previously did not live, increasing the risk of extinction for many. “It’s no longer about impacts in the future,” says Rachel Cleetus, a climate policy expert at the Union of Concerned Scientists. “It’s about what’s happening in the U.S. here and now, and around the world.”

No place on the planet is unaffected. In many areas, higher temperatures have led to major droughts, which dry out vegetation and provide additional fuel for wildfires such as those that have devastated Australia , the Mediterranean and western North America in recent years. The Colorado River , the source of water for tens of millions of people in the western United States , came under a water-shortage alert in 2021 for the first time in history.

Then there’s the Arctic, where temperatures are rising at more than twice the global average and communities are at the forefront of change. Permafrost is thawing, destabilizing buildings, pipelines and roads. Caribou and reindeer herders worry about the increased risk of parasites to the health of their animals. With less sea ice available to buffer the coast from storm erosion, the Inupiat village of Shishmaref, Alaska, risks crumbling into the sea. It will need to move from its sand-barrier island to the mainland .

“We know these changes are happening and that the Titanic is sinking,” says Louise Farquharson, a geomorphologist at the University of Alaska in Fairbanks who monitors permafrost and coastal change around Alaska. Like many Arctic scientists, she is working with Indigenous communities to understand the shifts they’re experiencing and what can be done when buildings start to slump and water supplies start to drain away. “A big part is just listening to community members and understanding what they’re seeing change,” she says.

All around the planet, those who depend on intact ecosystems for their survival face the greatest threat from climate change. And those with the least resources to adapt to climate change are the ones who feel it first .

“We are going to warm,” says Claudia Tebaldi, a climate scientist at Lawrence Berkeley National Laboratory in California. “There is no question about it. The only thing that we can hope to do is to warm a little more slowly.”

That’s one reason why the IPCC report released in 2021 focuses on anticipated levels of global warming. There is a big difference between the planet warming 1.5 degrees versus 2 degrees or 2.5 degrees. Consider that we are now at least 1.1 degrees above preindustrial levels of CO 2 and are already seeing dramatic shifts in climate. Given that, keeping further global temperature increases as low as possible will make a big difference in the climate impacts the planet faces. “With every fraction of a degree of warming, everything gets a little more intense,” says paleoclimatologist Jessica Tierney. “There’s no more time to beat around the bush.”

Historical and projected global temperature change

Various scenarios for how greenhouse gas emissions might change going forward help scientists predict future climate change. This graph shows the simulated historical temperature trend along with future projections of global surface temperature based on five scenarios from the Intergovernmental Panel on Climate Change. Temperature change is the difference from the 1850–1900 average.

The future rests on how much nations are willing to commit to cutting emissions and whether they will stick to those commitments. It’s a geopolitical balancing act the likes of which the world has never seen.

Science can and must play a role going forward. Improved climate models will illuminate what changes are expected at the regional scale, helping officials prepare. Governments and industry have crucial parts to play as well. They can invest in technologies, such as carbon sequestration, to help decarbonize the economy and shift society toward more renewable sources of energy. “We can solve these problems — most of the tools are already there,” says Cascade Tuholske, a geographer at Columbia University. “We just have to do it.”

Huge questions remain. Do voters have the will to demand significant energy transitions from their governments? How can business and military leaders play a bigger role in driving climate action? What should be the role of low-carbon energy sources that come with downsides, such as nuclear energy ? How can developing nations achieve a better standard of living for their people while not becoming big greenhouse gas emitters? How can we keep the most vulnerable from being disproportionately harmed during extreme events, and incorporate environmental and social justice into our future?

These questions become more pressing each year, as CO 2 accumulates in our atmosphere. The planet is now at higher levels of CO 2 than at any time in the last 3 million years. Yet Ralph Keeling, keeper of the iconic Mauna Loa record tracking the rise in atmospheric CO 2 , is already optimistically thinking about how scientists would be able to detect a slowdown, should the world actually start cutting emissions by a few percent per year. “That’s what the policy makers want to see — that there’s been some large-scale impact of what they did,” he says.

At the 2021 U.N. climate meeting in Glasgow diplomats from around the world agreed to work more urgently to shift away from using fossil fuels. They did not, however, adopt targets strict enough to keep the world below a warming of 1.5 degrees Celsius. It’s been well over a century since Svante Arrhenius recognized the consequences of putting extra carbon dioxide into the atmosphere, and yet world leaders have yet to pull together to avoid the most dangerous consequences of climate change.

Time is running out. — Alexandra Witze

Climate change facts

We know that climate change and its consequences are real, and we are responsible. Here’s what the science tells us.

How much has the planet warmed over the past century?

The planet’s average surface temperature has risen by at least 1.1 degree Celsius since preindustrial levels of 1850–1900.

What is causing climate change?

People are loading the atmosphere with carbon dioxide and other heat-trapping gases produced during the burning of fossil fuels, such as coal and gas, and cutting down forests.

What are some of the effects of climate change?

Ice sheets in Greenland and Antarctica are melting, raising sea levels and flooding low-lying island nations and coastal cities. Drought is parching farmlands and the rivers that feed them. Wildfires are raging. Rains are becoming more intense, and weather patterns are shifting.

What is the greenhouse effect?

In the 19th century, Irish physicist John Tyndall found that carbon dioxide gas, as well as water vapor, absorbed more heat than air alone. He argued that such gases would trap heat in Earth’s atmosphere, much as panes of glass trap heat in a greenhouse, and thus modulate climate.

What is the Keeling curve?

One of the most iconic datasets in all of science, the Keeling curve tracks the rise of atmospheric CO 2 . When geochemist Charles David Keeling began his measurements in 1958 on the Hawaiian volcano of Mauna Loa, CO 2 made up 315 parts per million of the global atmosphere. Each year the curve keeps going up: In 2016 it passed 400 ppm of CO 2 in the atmosphere, as measured during its typical annual minimum in September. In 2021, the annual minimum was 413 ppm.

Does it get hotter every year?

Average global temperatures fluctuate from year to year, but temperature observations taken at weather stations around the world confirm that we are living in the hottest years on record. The 10 warmest years since record keeping began in 1880 have all occurred since 2005. And nine of those 10 have come since 2010.

What countries emit the most carbon dioxide?

The United States has been the largest total emitter of carbon dioxide by far, followed by China and Russia. China’s annual CO 2 emissions surpassed those of the United States in 2006.

What places are impacted by climate change?

No place on the planet is unaffected. Higher temperatures have led to major droughts, providing fuel for wildfires such as those that have devastated Australia , the Mediterranean and western North America in recent years. The Colorado River came under a water-shortage alert in 2021 for the first time in history. In the Arctic, where temperatures are rising at more than twice the global average, permafrost is thawing, destabilizing buildings, pipelines and roads. With less sea ice available to buffer the coast from storm erosion, the Inupiat village of Shishmaref, Alaska, risks crumbling into the sea. All around the planet, those who depend on intact ecosystems for their survival face the greatest threat from climate change. And those with the least resources to adapt to climate change are the ones who feel it first .

Editor’s note: This story was published March 10, 2022.

British mathematician Lewis Fry Richardson (shown at center) proposes forecasting the weather by piecing together the calculations of tens of thousands of meteorologists working on small parts of the atmosphere.

Geochemist Charles David Keeling (shown in 1988) begins tracking the rise in atmospheric carbon dioxide at Mauna Loa in Hawaii. The record, which continues through today, has become one of the most iconic datasets in all of science.

Rachel Carson (shown) publishes the book Silent Spring , raising alarm over the ecological impacts of the pesticide DDT. The book helps catalyze the modern U.S. environmental movement.

The first Earth Day, organized by U.S. senator Gaylord Nelson and graduate student Denis Hayes, is celebrated.

The first Landsat satellite launched (shown), opening the door to continuous monitoring of Earth and its features from above.

A powerful eruption from the Philippines’ Mount Pinatubo (shown) ejects millions of tons of sulfur dioxide into the stratosphere, temporarily cooling the planet.  

World leaders gathered (shown) at the United Nations Conference on Environment and Development in Rio de Janeiro to address how to pursue economic development while also protecting the Earth. The meeting resulted in an international convention on climate change.

Activist Greta Thunberg initiates the “School Strike for Climate” movement by protesting outside the Swedish parliament. Soon, students around the world join a growing movement demanding action on climate change . (Activists at the 2021 U.N. Climate Change Conference are shown.)

From the archive

Climate change foreseen.

In an early mention of climate change in Science News-Letter , the predecessor of Science News , British meteorologist C.E.P. Brooks warns that present warming trends could lead to “important economic and political effects.”

IGY Brings Many Discoveries

Science News Letter lists the Top 8 accomplishments of the International Geophysical Year.

Chilling possibilities

Science News explores the tentative idea that global temperatures are cooling and that a new ice age could be imminent, which is later shown to be inaccurate.

Long Hot Future: Warmer Earth Appears Inevitable

“The planet earth will be a warmer place in the 21st century, and there is no realistic strategy that can prevent the change,” Science News reports.

Ozone and Global Warming: What to Do?

Policy makers discuss how to solve the dual problems of ozone depletion and global warming.

Looking for Mr. Greenhouse

Science writer Richard Monastersky reports on scientists’ efforts to evaluate how to connect increasing greenhouse gases and a warming climate.

World Climate Panel Charts Path for Action

The Intergovernmental Panel on Climate Change reports that “the fingerprint of man in the past temperature record” is now apparent.

Animals on the Move

A warming climate means shifting ranges and ecosystem disruptions for a lot of species, Nancy Ross-Flanigan reports.

Changing climate: 10 years after ‘An Inconvenient Truth’

A decade after former vice president Al Gore releases the documentary film An Inconvenient Truth , Science News looks back at how climate science has advanced.

With nowhere to hide from rising seas, Boston prepares for a wetter future

Mary Caperton Morton reports for Science News on how Boston is taking action to prepare for rising seas.

The new UN climate change report shows there’s no time for denial or delay

Earth & climate writer Carolyn Gramling covers the sixth assessment report from the Intergovernmental Panel on Climate Change, which documents how climate change is already affecting every region on Earth.

Climate change disinformation is evolving. So are efforts to fight back

Researchers are testing games and other ways to help people recognize climate change denial.

Extreme weather in 2022 showed the global impact of climate change

Heat waves, floods, wildfires and drought around the world were exacerbated by Earth’s changing climate.

It’s possible to reach net-zero carbon emissions. Here’s how

Cutting carbon dioxide emissions to curb climate change and reach net zero is possible but not easy.

The last 12 months were the hottest on record

The planet’s average temperature was about 1.3 degrees Celsius higher than the 1850–1900 average, a new report finds.

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Causes of Climate Change

Since the Industrial Revolution, human activities have released large amounts of carbon dioxide and other greenhouse gases into the atmosphere, which has changed the earth’s climate. Natural processes, such as changes in the sun's energy and volcanic eruptions, also affect the earth's climate. However, they do not explain the warming that we have observed over the last century. 1

Human Versus Natural Causes

It is unequivocal that human influence has warmed the atmosphere, ocean and land . - Intergovernmental Panel on Climate Change 4

Scientists have pieced together a record of the earth’s climate by analyzing a number of indirect measures of climate, such as ice cores, tree rings, glacier lengths, pollen remains, and ocean sediments, and by studying changes in the earth’s orbit around the sun. 2 This record shows that the climate varies naturally over a wide range of time scales, but this variability does not explain the observed warming since the 1950s. Rather, it is extremely likely (> 95%) that human activities have been the dominant cause of that warming. 3

Human activities have contributed substantially to climate change through:

• Greenhouse Gas Emissions

Reflectivity or Absorption of the Sun’s Energy

Heat-trapping greenhouse gases and the earth's climate, greenhouse gases.

Concentrations of the key greenhouse gases have all increased since the Industrial Revolution due to human activities. Carbon dioxide, methane, and nitrous oxide concentrations are now more abundant in the earth’s atmosphere than any time in the last 800,000 years. 5 These greenhouse gas emissions have increased the greenhouse effect and caused the earth’s surface temperature to rise . Burning fossil fuels changes the climate more than any other human activity.

Carbon dioxide: Human activities currently release over 30 billion tons of carbon dioxide into the atmosphere every year. 6 Atmospheric carbon dioxide concentrations have increased by more than 40 percent since pre-industrial times, from approximately 280 parts per million (ppm) in the 18th century 7 to 414 ppm in 2020. 8

Methane: Human activities increased methane concentrations during most of the 20th century to more than 2.5 times the pre-industrial level, from approximately 722 parts per billion (ppb) in the 18th century 9 to 1,867 ppb in 2019. 10

Nitrous oxide: Nitrous oxide concentrations have risen approximately 20 percent since the start of the Industrial Revolution, with a relatively rapid increase toward the end of the 20th century. Nitrous oxide concentrations have increased from a pre-industrial level of 270 ppb 11 to 332 ppb in 2019. 12

For more information on greenhouse gas emissions, see the Greenhouse Gas Emissions website. To learn more about actions that can reduce these emissions, see What You Can Do . To translate abstract greenhouse gas emissions measurements into concrete terms, try using EPA's Greenhouse Gas Equivalencies Calculator .

Activities such as agriculture, road construction, and deforestation can change the reflectivity of the earth's surface, leading to local warming or cooling. This effect is observed in heat islands , which are urban centers that are warmer than the surrounding, less populated areas. One reason that these areas are warmer is that buildings, pavement, and roofs tend to reflect less sunlight than natural surfaces. While deforestation can increase the earth’s reflectivity globally by replacing dark trees with lighter surfaces such as crops, the net effect of all land-use changes appears to be a small cooling. 13

Emissions of small particles, known as aerosols, into the air can also lead to reflection or absorption of the sun's energy. Many types of air pollutants undergo chemical reactions in the atmosphere to create aerosols. Overall, human-generated aerosols have a net cooling effect on the earth. Learn more about human-generated and natural aerosols .

Natural Processes

Natural processes are always influencing the earth’s climate and can explain climate changes prior to the Industrial Revolution in the 1700s. However, recent climate changes cannot be explained by natural causes alone.

Changes in the Earth’s Orbit and Rotation

Changes in the earth’s orbit and its axis of rotation have had a big impact on climate in the past. For example, the amount of summer sunshine on the Northern Hemisphere, which is affected by changes in the planet’s orbit, appears to be the primary cause of past cycles of ice ages, in which the earth has experienced long periods of cold temperatures (ice ages), as well as shorter interglacial periods (periods between ice ages) of relatively warmer temperatures. 14   At the coldest part of the last glacial period (or ice age), the average global temperature was about 11°F colder than it is today. At the peak of the last interglacial period, however, the average global temperature was at most 2°F warmer than it is today. 15

Variations in Solar Activity

Changes in the sun’s energy output can affect the intensity of the sunlight that reaches the earth’s surface. While these changes can influence the earth’s climate, solar variations have played little role in the climate changes observed in recent decades. 16 Satellites have been measuring the amount of energy the earth receives from the sun since 1978. These measurements show no net increase in the sun’s output, even as global surface temperatures have risen. 17

Changes in the Earth’s Reflectivity

The amount of sunlight that is absorbed or reflected by the planet depends on the earth’s surface and atmosphere. Dark objects and surfaces, like the ocean, forests, and soil, tend to absorb more sunlight. Light-colored objects and surfaces, like snow and clouds, tend to reflect sunlight. About 70 percent of the sunlight that reaches the earth is absorbed. 18 Natural changes in the earth’s surface, like the melting of sea ice , have contributed to climate change in the past, often acting as feedbacks  to other processes.

Volcanic Activity

Volcanoes have played a noticeable role in climate, and volcanic eruptions released large quantities of carbon dioxide in the distant past. Some explosive volcano eruptions can throw particles (e.g., SO 2 ) into the upper atmosphere, where they can reflect enough sunlight back to space to cool the surface of the planet for several years. 19 These particles are an example of cooling aerosols .

Volcanic particles from a single eruption do not produce long-term climate change because they remain in the atmosphere for a much shorter time than greenhouse gases. In addition, human activities emit more than 100 times as much carbon dioxide as volcanoes each year. 20

Changes in Naturally Occurring Carbon Dioxide Concentrations

Over the last several hundred thousand years, carbon dioxide levels varied in tandem with the glacial cycles. During warm interglacial periods, carbon dioxide levels were higher. During cool glacial periods, carbon dioxide levels were lower. 21 The heating or cooling of the earth’s surface and oceans can cause changes in the natural sources and sinks of these gases, and thus change greenhouse gas concentrations in the atmosphere. 22 These changing concentrations have acted as a positive climate feedback , amplifying the temperature changes caused by long-term shifts in the earth’s orbit. 23

1  National Academy of Sciences. (2020). Climate change: Evidence and causes: Update 2020 . The National Academies Press, Washington, DC, p. 5. doi: 10.17226/25733

2  Wuebbles, D.J., D.W. Fahey, K.A. Hibbard, B. DeAngelo, S. Doherty, K. Hayhoe, R. Horton, J.P. Kossin, P.C. Taylor, A.M. Waple & C.P. Weaver. (2017). Executive summary. In: Climate science special report: Fourth national climate assessment, volume I [Wuebbles, D.J., D.W. Fahey, K.A. Hibbard, D.J. Dokken, B.C. Stewart & T.K. Maycock (eds.)]. U.S. Global Change Research Program, Washington, DC, pp. 12–34, doi: 10.7930/J0DJ5CTG

National Academy of Sciences. (2020). Climate change: Evidence and causes: Update 2020 . The National Academies Press, Washington, DC, p. 5. doi: 10.17226/25733

3  IPCC (2013). Climate change 2013: The physical science basis .  Working Group I contribution to the fifth assessment report of the Intergovernmental Panel on Climate Change [Stocker, T.F., D. Qin, G.-K. Plattner, M. Tignor, S.K. Allen, J. Boschung, A. Nauels, Y. Xia, V. Bex & P.M. Midgley (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, p. 869.

4  IPCC. (2021). Climate change 2021: The physical science basis . Working Group I contribution to the sixth assessment report of the Intergovernmental Panel on Climate Change [Masson-Delmotte, V., P. Zhai, A. Pirani, S.L. Connors, C. Péan, S. Berger, N. Caud, Y. Chen, L. Goldfarb, M.I. Gomis, M. Huang, K. Leitzell, E. Lonnoy, J.B.R. Matthews, T.K. Maycock, T. Waterfield, O. Yelekçi, R. Yu & B. Zhou (eds.)]. Cambridge University Press, Cambridge, United Kingdom, p. SPM-5.

5  National Academy of Sciences. (2020). Climate change: Evidence and causes: Update 2020 . The National Academies Press, Washington, DC, p. B-2. doi: 10.17226/25733

Fahey, D.W., S.J. Doherty, K.A. Hibbard, A. Romanou & P.C. Taylor. (2017).  Physical drivers of climate change . In: Climate science special report: Fourth national climate assessment, volume I [Wuebbles, D.J., D.W. Fahey, K.A. Hibbard, D.J. Dokken, B.C. Stewart & T.K. Maycock (eds.)]. U.S. Global Change Research Program, Washington, DC, p. 80, Figure 2.4. doi: 10.7930/J0513WCR

6  Hayhoe, K., D.J. Wuebbles, D.R. Easterling, D.W. Fahey, S. Doherty, J. Kossin, W. Sweet, R. Vose & M. Wehner. (2018). Our changing climate . In: Impacts, risks, and adaptation in the United States: Fourth national climate assessment, volume II [Reidmiller, D.R., C.W. Avery, D.R. Easterling, K.E. Kunkel, K.L.M. Lewis, T.K. Maycock & B.C. Stewart (eds.)]. U.S. Global Change Research Program, Washington, DC, p. 76. doi: 10.7930/NCA4.2018

7  IPCC. (2013). Climate change 2013: The physical science basis . Working Group I contribution to the fifth assessment report of the Intergovernmental Panel on Climate Change [Stocker, T.F., D. Qin, G.-K. Plattner, M. Tignor, S.K. Allen, J. Boschung, A. Nauels, Y. Xia, V. Bex & P.M. Midgley (eds.)]. Cambridge University Press, Cambridge, United Kingdom, and New York, NY, p. 166.

8 NOAA. (2021). Trends in atmospheric carbon dioxide . Retrieved 3/25/2021. esrl.noaa.gov/gmd/ccgg/trends/mlo.html

9 IPCC. (2013).  Climate change 2013: The physical science basis . Working Group I contribution to the fifth assessment report of the Intergovernmental Panel on Climate Change [Stocker, T.F., D. Qin, G.-K. Plattner, M. Tignor, S.K. Allen, J. Boschung, A. Nauels, Y. Xia, V. Bex & P.M. Midgley (eds.)]. Cambridge University Press, Cambridge, United Kingdom, and New York, NY, p. 167.

10 NOAA. (2021). Trends in atmospheric methane . Retrieved 3/25/2021. esrl.noaa.gov/gmd/ccgg/trends_ch4

11 IPCC. (2013).  Climate change 2013: The physical science basis . Working Group I contribution to the fifth assessment report of the Intergovernmental Panel on Climate Change [Stocker, T.F., D. Qin, G.-K. Plattner, M. Tignor, S.K. Allen, J. Boschung, A. Nauels, Y. Xia, V. Bex & P.M. Midgley (eds.)]. Cambridge University Press, Cambridge, United Kingdom, and New York, NY, p. 168.

12 NOAA. (2021). Trends in nitrous oxide . Retrieved 3/25/2021. esrl.noaa.gov/gmd/ccgg/trends_n2o/

13 Fahey, D.W., S.J. Doherty, K.A. Hibbard, A. Romanou & P.C. Taylor. (2017). Physical drivers of climate change . In: Climate science special report: Fourth national climate assessment, volume I [Wuebbles, D.J., D.W. Fahey, K.A. Hibbard, D.J. Dokken, B.C. Stewart & T.K. Maycock (eds.)]. U.S. Global Change Research Program, Washington, DC, p. 78, Fig. 2.3 and p. 86. doi: 10.7930/J0513WCR

14  National Academy of Sciences. (2020). Climate change: Evidence and causes: Update 2020.  The National Academies Press, Washington, DC, p. 9. doi: 10.17226/25733

15  Fahey, D.W., S.J. Doherty, K.A. Hibbard, A. Romanou & P.C. Taylor. (2017). Our globally changing climate . In: Climate science special report: Fourth national climate assessment, volume I [Wuebbles, D.J., D.W. Fahey, K.A. Hibbard, D.J. Dokken, B.C. Stewart & T.K. Maycock (eds.)]. U.S. Global Change Research Program, Washington, DC, p. 53. doi: 10.7930/J08S4N35

16  National Academy of Sciences. (2020). Climate change: Evidence and causes: Update 2020.  The National Academies Press, Washington, DC, p. 7. doi: 10.17226/25733

17  National Academy of Sciences. (2020). Climate change: Evidence and causes: Update 2020.  The National Academies Press, Washington, DC, p. 7. doi: 10.17226/25733

18  Fahey, D.W., S.J. Doherty, K.A. Hibbard, A. Romanou, & P.C. Taylor. (2017). Physical drivers of climate change . In: Climate science special report: Fourth national climate assessment, volume I [Wuebbles, D.J., D.W. Fahey, K.A. Hibbard, D.J. Dokken, B.C. Stewart & T.K. Maycock (eds.)]. U.S. Global Change Research Program, Washington, DC, p. 2. doi: 10.7930/J0513WCR

19  Fahey, D.W., S.J. Doherty, K.A. Hibbard, A. Romanou, & P.C. Taylor. (2017). Physical drivers of climate change . In: Climate science special report: Fourth national climate assessment, volume I [Wuebbles, D.J., D.W. Fahey, K.A. Hibbard, D.J. Dokken, B.C. Stewart & T.K. Maycock (eds.)]. U.S. Global Change Research Program, Washington, DC, p. 79. doi: 10.7930/J0513WCR

20  Fahey, D.W., S.J. Doherty, K.A. Hibbard, A. Romanou & P.C. Taylor. (2017). Physical drivers of climate change . In: Climate science special report: Fourth national climate assessment, volume I [Wuebbles, D.J., D.W. Fahey, K.A. Hibbard, D.J. Dokken, B.C. Stewart & T.K. Maycock (eds.)]. U.S. Global Change Research Program, Washington, DC, p. 79. doi: 10.7930/J0513WCR

21  National Academy of Sciences. (2020). Climate change: Evidence and causes: Update 2020.  The National Academies Press, Washington, DC, pp. 9–10. doi: 10.17226/25733

22  IPCC. (2013).  Climate change 2013: The physical science basis .  Working Group I contribution to the fifth assessment report of the Intergovernmental Panel on Climate Change [Stocker, T.F., D. Qin, G.-K. Plattner, M. Tignor, S.K. Allen, J. Boschung, A. Nauels, Y. Xia, V. Bex & P.M. Midgley (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, p. 399.

23  National Academy of Sciences. (2020). Climate change: Evidence and causes: Update 2020.  The National Academies Press, Washington, DC, pp. 9–10. doi: 10.17226/25733

• Frequently Asked Questions

Scientists Agree: Global Warming is Happening and Humans are the Primary Cause

Published Aug 3, 2017 Updated Jan 9, 2018

The evidence is overwhelming. Record-breaking temperatures, humidity, and sea level rise, along with many other indicators, show that the Earth is warming fast, and that all the heat-trapping emissions we release into the atmosphere from burning fossil fuels is changing our climate.

The Climate Accountability Scorecard

The time to act is now. But action isn't easy: many powerful industry interests have hindered climate solutions and spread dangerous myths about climate change.

One of the preferred tactics these groups use to sow confusion is to promote studies that either ignore or misrepresent the evidence of thousands of articles published in well-established and well-respected scientific journals, which show that global warming is happening and that it is caused by humans.

No matter how much contrarians try to cloak reality, the evidence is not going away.

Widespread scientific consensus

Scientists worldwide agree that global warming is happening, and that human activity causes it.

The IPCC Fifth Assessment Report ( AR5 ), written by a panel of hundreds of climate experts and scientists from member countries of the World Meteorological Organization the United Nations Environmental Programme , plus a team of external reviewers, states unambiguously:

Human influence on the climate system is clear, and recent anthropogenic emissions of green-house gases are the highest in history. […] Warming of the climate system is unequivocal, and since the 1950s, many of the observed changes are unprecedented over decades to millennia. IPCC Fifth Assessment Report (AR5)

Building on two previous studies, a landmark 2013 peer-reviewed study evaluated 10,306 scientists to confirm that over 97 percent climate scientists agree, and over 97 percent of scientific articles find that global warming is real and largely caused by humans.

A 2016 peer-reviewed paper examined existing studies on consensus in climate research, and concluded that the 97 percent estimate is robust.

This level of consensus is equivalent to the level of agreement among scientists that smoking causes cancer – a statement that very few people, if any, contest today.

The US public also increasingly agrees that global warming is happening. A 2016 poll from Yale found that 70 percent of US residents believe global warming is happening, while record low numbers of people (12 percent) say the opposite.

A Gallup poll from 2017 showed that the number of people who worry “a great deal” about global warming has increased from 37 percent in 2016 to 45 percent in 2017.  The acceptance of human-caused emissions as the cause of warming is not keeping pace with those that believe it is happening, but it is at 53 percent.

There is no shortage of published research on the consensus of climate scientists and climate science when it comes to human-caused global warming. In addition to the references above, you can read about how the discussion on consensus developed over time in these studies .

Many different scientific societies in the United States and numerous national academies of science from around the world have also issued statements that verify the scientific claims about human-caused warming (see below).

Consensus and scientific uncertainty

Climate skeptics and deniers often misrepresent and aggrandize “ scientific uncertainty ” to undermine climate science consensus. When it comes to scientific consensus on global warming, it is important to clarify what type of uncertainty exists, and what type does not: there is strong certainty on the types of impacts that global warming is causing (or would be likely to cause under a given scenario for emissions), but less certainty on the exact timing and intensity of these impacts.  

When Rising Seas Hit Home

For instance, on the issue of sea level rise, we know with certainty that it will happen – it is already happening – and projections under different scenarios give us a range of possible rise.  We don’t know an exact value, however, for future sea level rise, because in large part it is dependent on the rate of future emissions, which is unknown.  

If emissions continue in a “business as usual” fashion, the sea level rise will be closer to the higher range of projections. But if we significantly reduce emissions, the rise will be closer to the lower levels of projections.

The same is true for how much warming will actually happen, or how much land-based ice and glaciers will melt. All these things are already happening, but future rates are not known because they, too, depend on the rate of future emissions. What scientists can calculate quite confidently is a narrow range of outcomes within a given scenario—meaning the likely highest and lowest values  if we continue on a certain path of emissions. This information is critical to making smart collective choices and for planning for the future.

Uncertainties are not a reason to delay action on climate change. Quite the contrary: those uncertainties are really a consequence of our collective choices, and a risk we must prepare for.

You can think about it like car insurance: everyone hopes they won’t be in a car accident but have accident insurance anyway, even though the likelihood is very low.

Climate adaptation and climate risk reduction are “insurance” against the effects of climate change, which in contrast are NOT low-probability events, but highly likely and predicted with high levels of certainty under specific conditions.  Being prepared for these scenarios is simply smart planning. Nobody wants to be caught unaware and unprepared.

Killer Heat in the United States

Consensus worldwide.

Many scientific societies and academies have released statements and studies that highlight the overwhelming consensus on climate change science.

American Association for the Advancement of Science: AAAS Reaffirms the Reality of Human-Caused Climate Change “Observations throughout the world make it clear that climate change is occurring, and rigorous scientific research concludes that the greenhouse gases emitted by human activities are the primary driver. This conclusion is based on multiple independent lines of evidence and the vast body of peer-reviewed science.” (June 2016)

American Chemical Society : Statement on Global Climate Change “The Earth’s climate is changing in response to increasing concentrations of greenhouse gases (GHGs) and particulate matter in the atmosphere, largely as the result of human activities. … Unmitigated climate change will lead to increases in extreme weather events and will cause significant sea level rise, causing property damage and population displacement. It also will continue to degrade ecosystems and natural resources, affecting food and water availability and human health, further burdening economies and societies. Continued uncontrolled GHG emissions will accelerate and compound the effects and risks of climate change well into the future.” (2016)

American Geophysical Union : Human-induced Climate Change Requires Urgent Action.

"Extensive, independent observations confirm the reality of global warming. These observations show large-scale increases in air and sea temperatures, sea level, and atmospheric water vapor; they document decreases in the extent of mountain glaciers, snow cover, permafrost, and Arctic sea ice. These changes are broadly consistent with long-understood physics and predictions of how the climate system is expected to respond to human-caused increases in greenhouse gases. The changes are inconsistent with explanations of climate change that rely on known natural influences.”(December 2003, revised and reaffirmed December 2007, February 2012, August 2013)

American Meteorological Society: Climate Change: An Information Statement of the American Meteorological Society "It is clear from extensive scientific evidence that the dominant cause of the rapid change in climate of the past half century is human-induced increases in the amount of atmospheric greenhouse gases, including carbon dioxide (CO2), chlorofluorocarbons, methane, and nitrous oxide.” (August 2012)

American Physical Society : Statement on Earth’s Changing Climate

"While natural sources of climate variability are significant, multiple lines of evidence indicate that human influences have had an increasingly dominant effect on global climate warming observed since the mid-twentieth century. Although the magnitudes of future effects are uncertain, human influences on the climate are growing." (November 2015)

Geological Society of America : Position Statement on Climate Change "Scientific advances have greatly reduced previous uncertainties about recent global warming. Ground-station measurements have shown a warming trend of ~0.85 °C since 1880, a trend consistent with (1) retreat of northern hemisphere snow and Arctic sea ice; (2) greater heat storage in the ocean; (3) retreat of most mountain glaciers; (4) an ongoing rise in global sea level; and (5) proxy reconstructions of temperature change over past centuries from archives that include ice cores, tree rings, lake sediments, boreholes, cave deposits, and corals." (October 2006; revised April 2010, March 2013, April 2015).

Intergovernmental Panel on Climate Change: Synthesis Report Summary for Policymakers

“Human influence on the climate system is clear, and recent anthropogenic emissions of green-house gases are the highest in history. Recent climate changes have had widespread impacts on human and natural systems. “Warming of the climate system is unequivocal, and since the 1950s, many of the observed changes are unprecedented over decades to millennia. The atmosphere and ocean have warmed, the amounts of snow and ice have diminished, and sea level has risen.” (2014)

International academies joint statement: Global response to climate change

“The world’s climate is changing, and the impacts are already being observed. Changing agricultural conditions, ocean warming and acidification, rising sea levels, and increased frequency and intensity of many extreme weather events are impacting infrastructure, environmental assets and human health.” (2018, African Academy of Sciences and the national academies of science of the United Kingdom, Australia, Bangladesh, Botswana, Canada, India, Mauritius, Mozambique, Nigeria, Pakistan, New Zealand, Cyprus, Singapore, Sri Lanka, South Africa, Scotland, Zimbabwe, Kenya, Zambia, Malaysia, Cameroon). 

US Global Change Research Program:  Highlights of the Findings of the U.S. Global Change Research Program Climate Science Special Report

“Based on extensive evidence, … it is extremely likely that human activities, especially emissions of greenhouse gases, are the dominant cause of the observed warming since the mid-20th century. For the warming over the last century, there is no convincing alternative explanation supported by the extent of the observational evidence.

“In addition to warming, many other aspects of global climate are changing, primarily in response to human activities. Thousands of studies conducted by researchers around the world have documented changes in surface, atmospheric, and oceanic temperatures; melting glaciers; diminishing snow cover; shrinking sea ice; rising sea levels; ocean acidification; and increasing atmospheric water vapor.” (November 2017)

U.S. National Academy of Sciences : Understanding and Responding to Climate Change "The scientific understanding of climate change is now sufficiently clear to begin taking steps to prepare for climate change and to slow it." (2008)

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Human, economic, environmental toll of climate change on the rise: WMO

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The relentless advance of climate change brought more drought, flooding and heatwaves to communities around the world last year, compounding threats to people’s lives and livelihoods, the UN’s World Meteorological Organization ( WMO ) said on Friday.

WMO latest State of the Global Climate report shows that the last eight years were the eight warmest on record , and that sea level rise and ocean warming hit new highs . Record levels of greenhouse gases caused “planetary scale changes on land, in the ocean and in the atmosphere”.

World Meteorological Organization April 21, 2023

The organization says its report, released ahead of this year’s Mother Earth Day , echoes UN Secretary-General António Guterres ’ call for “ deeper, faster emissions cuts to limit global temperature rise to 1.5 degree Celsius”, as well as “ massively scaled-up investments in adaptation and resilience, particularly for the most vulnerable countries and communities who have done the least to cause the crisis”.

WMO Secretary-General, Prof. Petteri Taalas, said that amid rising greenhouse gas emissions and a changing climate, “populations worldwide continue to be gravely impacted by extreme weather and climate events ”. He stressed that last year, “continuous drought in East Africa, record breaking rainfall in Pakistan and record-breaking heatwaves in China and Europe affected tens of millions, drove food insecurity, boosted mass migration, and cost billions of dollars in loss and damage.”

WMO highlights the importance of investing in climate monitoring and early warning systems to help mitigate the humanitarian impacts of extreme weather. The report also points out that today, improved technology makes the transition to renewable energy “cheaper and more accessible than ever” .

Warmest years on record

The State of the Global Climate report complements the Intergovernmental Panel on Climate Change ( IPCC ) Sixth Assessment report released a month ago, which includes data up to 2020.

WMO’s new figures show that global temperatures have continued to rise, making the years 2015 to 2022 the eight warmest ever since regular tracking started in 1850. WMO notes that this was despite three consecutive years of a cooling La Niña climate pattern.

WMO says concentrations of the three main greenhouse gases, which trap heat in the atmosphere – carbon dioxide, methane, and nitrous oxide – reached record highs in 2021, which is the latest year for which consolidated data is available , and that there are indications of a continued increase in 2022.

Indicators ‘off the charts’

According to the report, “melting of glaciers and sea level rise - which again reached record levels in 2022 - will continue to up to thousands of years ”. WMO further highlights that “Antarctic sea ice fell to its lowest extent on record and the melting of some European glaciers was, literally, off the charts”.

Sea level rise, which threatens the existence of coastal communities and sometimes entire countries, has been fuelled not only by melting glaciers and ice caps in Greenland and Antarctica, but also by the expansion of the volume of oceans due to heat. WMO notes that ocean warming has been “particularly high in the past two decades”.

Deadly consequences

The report examines the many socio-economic impacts of extreme weather, which have wreaked havoc in the lives of the most vulnerable around the world . Five consecutive years of drought in East Africa, in conjunction with other factors such as armed conflict, have brought devastating food insecurity to 20 million people across the region.

Extensive flooding in Pakistan caused by severe rainfall in July and August last year killed over 1,700 people, while some 33 million were affected. WMO highlights that total damage and economic losses were assessed at $30 billion, and that by October 2022, around 8 million people had been internally displaced by the floods.

The report also notes that in addition to putting scores of people on the move, throughout the year, hazardous climate and weather-related events “worsened conditions” for many of the 95 million people already living in displacement .

Threat to ecosystems

Environmental impacts of climate change are another focus of the report, which highlights a shift in recurring events in nature, “such as when trees blossom, or birds migrate”. The flowering of cherry trees in Japan has been tracked since the ninth century, and in 2021 the date of the event was the earliest recorded in 1,200 years .

As a result of such shifts, entire ecosystems can be upended . WMO notes that spring arrival times of over a hundred European migratory bird species over five decades “show increasing levels of mismatch to other spring events”, such as the moment when trees produce leaves and insects take flight, which are important for bird survival.

The report says these mismatches “are likely to have contributed to population decline in some migrant species , particularly those wintering in sub-Saharan Africa”, and to the ongoing destruction of biodiversity.

Ending the ‘war on nature’

In his message on Earth Day, UN chief Mr. Guterres warned that “ biodiversity is collapsing as one million species teeter on the brink of extinction ”, and called on the world to end its “relentless and senseless wars on nature”, insisting that “we have the tools, the knowledge, and the solutions” to address climate change.

Last month, Mr. Guterres convened an Advisory Panel of top UN agency officials, private sector and civil society leaders, to help fast track a global initiative aiming to protect all countries through life-saving early warning systems by 2027. Stepped up coordinated action was announced, initially in 30 countries particularly vulnerable to extreme weather, including Small Island Developing States and Least Developed Countries.

Early Warnings for All

WMO Secretary-General Prof. Petteri Taalas said on Friday that some one hundred countries currently do not have adequate weather services in place, and that the UN Early Warnings for All Initiative “ aims to fill the existing capacity gap to ensure that every person on earth is covered by early warning services”.

Mr. Taalas explained that “achieving this ambitious task requires improvement of observation networks, investments in early warning, hydrological and climate service capacities.” He also stressed the effectiveness of collaboration among UN agencies in addressing humanitarian impacts of climate events, especially in reducing mortality and economic losses. 

• extreme weather
• climate action

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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• Published: 07 August 2024

Climate change debates

Nature Climate Change volume  14 ,  page 769 ( 2024 ) Cite this article

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• Climate change
• Climate-change adaptation
• Climate-change ecology
• Climate-change mitigation

From a scientific standpoint, the causes of current ongoing climate change are well established. But in the context of rapid change, and real-world consequences, there is still room — and need — for scientific discussion in climate change fields.

Science, while ultimately grounded on the concept of knowledge, has always been a rich and often controversial stage for debate. While many scientific debates have been effectively ‘solved’ by further acquisition of knowledge (for example, heliocentrism versus geocentrism), others remain ripe for discussion. Examples include big questions about the origins of life on Earth, the potential for life outside this planet, or the ultimate impacts of artificial intelligence.

In the climate change field, the big questions have historically been those related to the recognition and acceptance of anthropogenic climate change. While the intensity of climate change debates has been partly fuelled by personal and political desires, the field remains wide open for debate even within more purely scientific realms due to its strong focus on future events. Past debates have now evolved into discussions on the details of what will happen when (and where), as well as weighing up the potential and pitfalls of different modes of action or inaction.

For example, in this issue of Nature Climate Change , we feature several pieces related to the complicated debate of how to best prioritize the conservation of species and their ecosystem functions in the context of rapid change, including discussion on the role of active human intervention. Among these, three independently written pieces on the conservation of corals highlight different, and sometimes opposing, priorities for future action.

In a Comment , Timothy McClanahan stresses that a focus on broad narratives of global coral loss, rather than acknowledging heterogeneities, caveats and uncertainty, will hinder management and muddy public communication. In their Comment , Robert Streit and colleagues argue for a minimal intervention approach in managing corals, questioning whether a human desire to ‘act heroically’ might hinder decision-making and be counterproductive. By contrast, Michael Webster and Daniel Schindler suggest in another Comment that ecological replacement — whereby corals lost to global change are replaced with species providing similar ecosystem functions — should be considered, urging that the potential risks of such actions are weighed against the risks of not intervening.

In a separate research Article , Silvio Schueler and colleagues focus on just one part of this ‘risk of inaction’ in a forest context, to demonstrate that while assisted migration (moving species and populations in response to climate change) can maintain or improve carbon stocks, failing to do so could result in large future carbon sink losses. Discussions related to active manipulation and movement of species have been historically more open when plants rather than animals (even relatively sessile animals, such as coral) are involved, particularly in artificial contexts such as crop or forestry plantations. Nonetheless, the wider debate remains in its infancy. In highlighting the potential, Schueler and colleagues call for more research to quantify the trade-offs between the opportunities and risks of implementation.

The topics here represent just a fraction of the ongoing debates in climate change circles. Recent examples range from questions related to the feasibility of large-scale carbon dioxide removal deployment ( Nat. Clim. Change 14 , 549; 2024 ), different opinions on geoengineering research and implementation , or altering the chemistry of the atmosphere to degrade methane ( Q. Li et al. Nat. Commun. 14 , 4045; 2023 ). Beyond that, many climate change debates have a common theme at their core — that regardless of the findings, any future possibilities should not be considered as an alternative for active mitigation.

Many of these are likely to be debated for some time to come as both science and time progress. We look forward to these debates, and hope that active discussion can help push science forward.

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Global Energy Crisis

How the energy crisis started, how global energy markets are impacting our daily life, and what governments are doing about it

• English English

What is the energy crisis?

Record prices, fuel shortages, rising poverty, slowing economies: the first energy crisis that's truly global.

Energy markets began to tighten in 2021 because of a variety of factors, including the extraordinarily rapid economic rebound following the pandemic. But the situation escalated dramatically into a full-blown global energy crisis following Russia’s invasion of Ukraine in February 2022. The price of natural gas reached record highs, and as a result so did electricity in some markets. Oil prices hit their highest level since 2008. 

Higher energy prices have contributed to painfully high inflation, pushed families into poverty, forced some factories to curtail output or even shut down, and slowed economic growth to the point that some countries are heading towards severe recession. Europe, whose gas supply is uniquely vulnerable because of its historic reliance on Russia, could face gas rationing this winter, while many emerging economies are seeing sharply higher energy import bills and fuel shortages. While today’s energy crisis shares some parallels with the oil shocks of the 1970s, there are important differences. Today’s crisis involves all fossil fuels, while the 1970s price shocks were largely limited to oil at a time when the global economy was much more dependent on oil, and less dependent on gas. The entire word economy is much more interlinked than it was 50 years ago, magnifying the impact. That’s why we can refer to this as the first truly global energy crisis.

Some gas-intensive manufacturing plants in Europe have curtailed output because they can’t afford to keep operating, while in China some have simply had their power supply cut. In emerging and developing economies, where the share of household budgets spent on energy and food is already large, higher energy bills have increased extreme poverty and set back progress towards achieving universal and affordable energy access. Even in advanced economies, rising prices have impacted vulnerable households and caused significant economic, social and political strains.

Climate policies have been blamed in some quarters for contributing to the recent run-up in energy prices, but there is no evidence. In fact, a greater supply of clean energy sources and technologies would have protected consumers and mitigated some of the upward pressure on fuel prices.

Russia's invasion of Ukraine drove European and Asian gas prices to record highs

Evolution of key regional natural gas prices, june 2021-october 2022, what is causing it, disrupted supply chains, bad weather, low investment, and then came russia's invasion of ukraine.

Energy prices have been rising since 2021 because of the rapid economic recovery, weather conditions in various parts of the world, maintenance work that had been delayed by the pandemic, and earlier decisions by oil and gas companies and exporting countries to reduce investments. Russia began withholding gas supplies to Europe in 2021, months ahead of its invasion of Ukraine. All that led to already tight supplies. Russia’s attack on Ukraine greatly exacerbated the situation . The United States and the EU imposed a series of sanctions on Russia and many European countries declared their intention to phase out Russian gas imports completely. Meanwhile, Russia has increasingly curtailed or even turned off its export pipelines. Russia is by far the world’s largest exporter of fossil fuels, and a particularly important supplier to Europe. In 2021, a quarter of all energy consumed in the EU came from Russia. As Europe sought to replace Russian gas, it bid up prices of US, Australian and Qatari ship-borne liquefied natural gas (LNG), raising prices and diverting supply away from traditional LNG customers in Asia. Because gas frequently sets the price at which electricity is sold, power prices soared as well. Both LNG producers and importers are rushing to build new infrastructure to increase how much LNG can be traded internationally, but these costly projects take years to come online. Oil prices also initially soared as international trade routes were reconfigured after the United States, many European countries and some of their Asian allies said they would no longer buy Russian oil. Some shippers have declined to carry Russian oil because of sanctions and insurance risk. Many large oil producers were unable to boost supply to meet rising demand – even with the incentive of sky-high prices – because of a lack of investment in recent years. While prices have come down from their peaks, the outlook is uncertain with new rounds of European sanctions on Russia kicking in later this year.

What is being done?

Pandemic hangovers and rising interest rates limit public responses, while some countries turn to coal.

Some governments are looking to cushion the blow for customers and businesses, either through direct assistance, or by limiting prices for consumers and then paying energy providers the difference. But with inflation in many countries well above target and budget deficits already large because of emergency spending during the Covid-19 pandemic, the scope for cushioning the impact is more limited than in early 2020. Rising inflation has triggered increases in short-term interest rates in many countries, slowing down economic growth. Europeans have rushed to increase gas imports from alternative producers such as Algeria, Norway and Azerbaijan. Several countries have resumed or expanded the use of coal for power generation, and some are extending the lives of nuclear plants slated for de-commissioning. EU members have also introduced gas storage obligations, and agreed on voluntary targets to cut gas and electricity demand by 15% this winter through efficiency measures, greater use of renewables, and support for efficiency improvements. To ensure adequate oil supplies, the IEA and its members responded with the two largest ever releases of emergency oil stocks. With two decisions – on 1 March 2022 and 1 April – the IEA coordinated the release of some 182 million barrels of emergency oil from public stocks or obligated stocks held by industry. Some IEA member countries independently released additional public stocks, resulting in a total of over 240 million barrels being released between March and November 2022.

The IEA has also published action plans to cut oil use with immediate impact, as well as plans for how Europe can reduce its reliance on Russian gas and how common citizens can reduce their energy consumption . The invasion has sparked a reappraisal of energy policies and priorities, calling into question the viability of decades of infrastructure and investment decisions, and profoundly reorientating international energy trade. Gas had been expected to play a key role in many countries as a lower-emitting "bridge" between dirtier fossil fuels and renewable energies. But today’s crisis has called into question natural gas’ reliability.

The current crisis could accelerate the rollout of cleaner, sustainable renewable energy such as wind and solar, just as the 1970s oil shocks spurred major advances in energy efficiency, as well as in nuclear, solar and wind power. The crisis has also underscored the importance of investing in robust gas and power network infrastructure to better integrate regional markets. The EU’s RePowerEU, presented in May 2022 and the United States’ Inflation Reduction Act , passed in August 2022, both contain major initiatives to develop energy efficiency and promote renewable energies. 

The global energy crisis can be a historic turning point

Energy saving tips

1. Heating: turn it down

Lower your thermostat by just 1°C to save around 7% of your heating energy and cut an average bill by EUR 50-70 a year. Always set your thermostat as low as feels comfortable, and wear warm clothes indoors. Use a programmable thermostat to set the temperature to 15°C while you sleep and 10°C when the house is unoccupied. This cuts up to 10% a year off heating bills. Try to only heat the room you’re in or the rooms you use regularly.

The same idea applies in hot weather. Turn off air-conditioning when you’re out. Set the overall temperature 1 °C warmer to cut bills by up to 10%. And only cool the room you’re in.

2. Boiler: adjust the settings

Default boiler settings are often higher than you need. Lower the hot water temperature to save 8% of your heating energy and cut EUR 100 off an average bill.  You may have to have the plumber come once if you have a complex modern combi boiler and can’t figure out the manual. Make sure you follow local recommendations or consult your boiler manual. Swap a bath for a shower to spend less energy heating water. And if you already use a shower, take a shorter one. Hot water tanks and pipes should be insulated to stop heat escaping. Clean wood- and pellet-burning heaters regularly with a wire brush to keep them working efficiently.

3. Warm air: seal it in

Close windows and doors, insulate pipes and draught-proof around windows, chimneys and other gaps to keep the warm air inside. Unless your home is very new, you will lose heat through draughty doors and windows, gaps in the floor, or up the chimney. Draught-proof these gaps with sealant or weather stripping to save up to EUR 100 a year. Install tight-fitting curtains or shades on windows to retain even more heat. Close fireplace and chimney openings (unless a fire is burning) to stop warm air escaping straight up the chimney. And if you never use your fireplace, seal the chimney to stop heat escaping.

4. Lightbulbs: swap them out

Replace old lightbulbs with new LED ones, and only keep on the lights you need. LED bulbs are more efficient than incandescent and halogen lights, they burn out less frequently, and save around EUR 10 a year per bulb. Check the energy label when buying bulbs, and aim for A (the most efficient) rather than G (the least efficient). The simplest and easiest way to save energy is to turn lights off when you leave a room.

5. Grab a bike

Walking or cycling are great alternatives to driving for short journeys, and they help save money, cut emissions and reduce congestion. If you can, leave your car at home for shorter journeys; especially if it’s a larger car. Share your ride with neighbours, friends and colleagues to save energy and money. You’ll also see big savings and health benefits if you travel by bike. Many governments also offer incentives for electric bikes.

6. Use public transport

For longer distances where walking or cycling is impractical, public transport still reduces energy use, congestion and air pollution. If you’re going on a longer trip, consider leaving your car at home and taking the train. Buy a season ticket to save money over time. Your workplace or local government might also offer incentives for travel passes. Plan your trip in advance to save on tickets and find the best route.

7. Drive smarter

Optimise your driving style to reduce fuel consumption: drive smoothly and at lower speeds on motorways, close windows at high speeds and make sure your tires are properly inflated. Try to take routes that avoid heavy traffic and turn off the engine when you’re not moving. Drive 10 km/h slower on motorways to cut your fuel bill by around EUR 60 per year. Driving steadily between 50-90 km/h can also save fuel. When driving faster than 80 km/h, it’s more efficient to use A/C, rather than opening your windows. And service your engine regularly to maintain energy efficiency.

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Deadly Landslides in India Made Worse by Climate Change, Study Finds

Extreme rainfall made 10 percent heavier by human-caused climate change triggered landslides that killed hundreds, according to a new study.

By Austyn Gaffney

A sudden burst of rainfall on July 30 caused a cascade of landslides that buried hundreds of people in the mountainous Kerala region of southern India.

That downpour was 10 percent heavier because of human-caused climate change, according to a study by World Weather Attribution, a group of scientists who quantify how climate change can influence extreme weather. Nearly six inches, or 150 millimeters, of rain fell on soils already highly saturated from two months of monsoon and marked the third highest single-day rain event on record for India.

“The devastation in northern Kerala is concerning not only because of the difficult humanitarian situation faced by thousands today, but also because this disaster occurred in a continually warming world,” said Maja Vahlberg, a climate risk consultant at the Red Cross Red Crescent Climate Centre. “The increase in climate-change-driven rainfall found in this study is likely to increase the number of landslides that could be triggered in the future.”

In a state that is highly prone to landslides, the Wayanad district is considered the riskiest part. As of Tuesday, at least 231 people had died and 100 remained missing.

The Kerala landslides were the second extreme landslide event in July, following one in Ethiopia that killed 257 people. July was the second-worst month on record, after July 2019, with 95 landslide events that caused 1,167 fatalities , according to data maintained by Dave Petley, the vice-chancellor of the University of Hull. Together, they caused roughly one-third of the more than 3,600 deaths resulting from some 429 fatal landslides recorded this year, Dr. Petley said in an email.

Already, 2024 is an outlier, Dr. Petley posted to The Landslide Blog on Tuesday . He wrote that he could “only speculate on the likely underlying reasons for this very high incidence of fatal landslides,” but “the most likely cause continues to be the exceptionally high global surface temperatures, and the resultant increase in high intensity rainfall events.”

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