what is the main cause of climate change essay

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

• Share this page block

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.

This NRDC.org story is available for online republication by news media outlets or nonprofits under these conditions: The writer(s) must be credited with a byline; you must note prominently that the story was originally published by NRDC.org and link to the original; the story cannot be edited (beyond simple things such as grammar); you can’t resell the story in any form or grant republishing rights to other outlets; you can’t republish our material wholesale or automatically—you need to select stories individually; you can’t republish the photos or graphics on our site without specific permission; you should drop us a note to let us know when you’ve used one of our stories.

We need climate action to be a top priority in Washington!

Tell President Biden and Congress to slash climate pollution and reduce our dependence on fossil fuels.

Urge President Biden and Congress to make equitable climate action a top priority

2023 was the hottest year on record, underscoring the urgency of shifting to clean energy and curbing the carbon pollution that is driving the climate crisis. President Biden and Congress have the tools to get the job done.

Related Stories

Greenhouse Effect 101

What Are the Solutions to Climate Change?

Failing to Meet Our Climate Goals Is Not an Option

When you sign up, you’ll become a member of NRDC’s Activist Network. We will keep you informed with the latest alerts and progress reports.

Search the United Nations

• What Is Climate Change
• Myth Busters
• Renewable Energy
• Finance & Justice
• Initiatives
• Sustainable Development Goals
• Paris Agreement
• Climate Ambition Summit 2023
• Climate Conferences
• Press Material
• Communications Tips

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. 

Heatwaves put bees at risk

Eleven-year-old Markela is a fifth generation beekeeper, but climate change is making it so that she may not be able to carry on the family tradition. Wildfires, heatwaves, and droughts that are increasing in intensity and frequency due to the climate crisis, put bees and the ecosystems at risk.

Healing Chile’s Huapi Island

On Chile’s Huapi Island, native forests have become fragmented, making the soils poorer and drier and leaving the population vulnerable to the effects of climate change. Now, thanks to the restoration efforts of Indigenous Peoples, native trees are making a comeback.

Early warning systems are saving lives in Central Asia

As Central Asia grapples with the increasing frequency and severity of climate-induced hazards, the importance of robust early warning systems cannot be overstated. However, countries need both technical knowledge and resources to effectively implement these systems on a large scale. Japan has been a reliable ally for countries, helping advance early warning systems and increase resilience in the region.

Facts and figures

• What is climate change?
• Causes and effects
• Myth busters

Cutting emissions

• Explaining net zero
• High-level expert group on net zero
• Checklists for credibility of net-zero pledges
• Greenwashing
• What you can do

Clean energy

• Renewable energy – key to a safer future
• What is renewable energy
• Five ways to speed up the energy transition
• Why invest in renewable energy
• Clean energy stories
• A just transition

Adapting to climate change

• Climate adaptation
• Early warnings for all
• Youth voices

Financing climate action

• Finance and justice
• Loss and damage
• $100 billion commitment
• Why finance climate action
• Biodiversity
• Human Security

International cooperation

• What are Nationally Determined Contributions
• Acceleration Agenda
• Climate Ambition Summit
• Climate conferences (COPs)
• Youth Advisory Group
• Action initiatives
• Secretary-General’s speeches
• Press material
• Fact sheets
• Communications tips

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

Related Topics

• CLIMATE CHANGE
• ENVIRONMENT AND CONSERVATION
• AIR POLLUTION

You May Also Like

Another weapon to fight climate change? Put carbon back where we found it

How global warming is disrupting life on Earth

Are there real ways to fight climate change? Yes.

What is the ozone layer, and why does it matter?

The U.S. ‘warming hole’—a climate anomaly explained

• Environment
• Paid Content

History & Culture

• History & Culture
• Terms of Use
• Privacy Policy
• Your US State Privacy Rights
• Children's Online Privacy Policy
• Interest-Based Ads
• About Nielsen Measurement
• Do Not Sell or Share My Personal Information
• Nat Geo Home
• Attend a Live Event
• Book a Trip
• Inspire Your Kids
• Shop Nat Geo
• Visit the D.C. Museum
• Learn About Our Impact
• Support Our Mission
• Advertise With Us
• Customer Service
• Renew Subscription
• Manage Your Subscription
• Work at Nat Geo
• Sign Up for Our Newsletters
• Contribute to Protect the Planet

Copyright © 1996-2015 National Geographic Society Copyright © 2015-2024 National Geographic Partners, LLC. All rights reserved

What evidence exists that Earth is warming and that humans are the main cause?

We know the world is warming because people have been recording daily high and low temperatures at thousands of weather stations worldwide, over land and ocean, for many decades and, in some locations, for more than a century. When different teams of climate scientists in different agencies (e.g., NOAA and NASA) and in other countries (e.g., the U.K.’s Hadley Centre) average these data together, they all find essentially the same result: Earth’s average surface temperature has risen by about 1.8°F (1.0°C) since 1880. 

( bar chart ) Yearly temperature compared to the twentieth-century average from 1850–2023. Red bars mean warmer-than-average years; blue bars mean colder-than-average years. (line graph) Atmospheric carbon dioxide amounts: 1850-1958 from IAC , 1959-2023 from NOAA Global Monitoring Lab . NOAA Climate.gov graph, adapted from original by Dr. Howard Diamond (NOAA ARL).

In addition to our surface station data, we have many different lines of evidence that Earth is warming ( learn more ). Birds are migrating earlier, and their migration patterns are changing.  Lobsters  and  other marine species  are moving north. Plants are blooming earlier in the spring. Mountain glaciers are melting worldwide, and snow cover is declining in the Northern Hemisphere (Learn more  here  and  here ). Greenland’s ice sheet—which holds about 8 percent of Earth’s fresh water—is melting at an accelerating rate ( learn more ). Mean global sea level is rising ( learn more ). Arctic sea ice is declining rapidly in both thickness and extent ( learn more ).

The Greenland Ice Sheet lost mass again in 2020, but not as much as it did 2019. Adapted from the 2020 Arctic Report Card, this graph tracks Greenland mass loss measured by NASA's GRACE satellite missions since 2002. The background photo shows a glacier calving front in western Greenland, captured from an airplane during a NASA Operation IceBridge field campaign. Full story.

We know this warming is largely caused by human activities because the key role that carbon dioxide plays in maintaining Earth’s natural greenhouse effect has been understood since the mid-1800s. Unless it is offset by some equally large cooling influence, more atmospheric carbon dioxide will lead to warmer surface temperatures. Since 1800, the amount of carbon dioxide in the atmosphere  has increased  from about 280 parts per million to 410 ppm in 2019. We know from both its rapid increase and its isotopic “fingerprint” that the source of this new carbon dioxide is fossil fuels, and not natural sources like forest fires, volcanoes, or outgassing from the ocean.

Philip James de Loutherbourg's 1801 painting, Coalbrookdale by Night , came to symbolize the start of the Industrial Revolution, when humans began to harness the power of fossil fuels—and to contribute significantly to Earth's atmospheric greenhouse gas composition. Image from Wikipedia .

Finally, no other known climate influences have changed enough to account for the observed warming trend. Taken together, these and other lines of evidence point squarely to human activities as the cause of recent global warming.

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 .

National Fish, Wildlife, and Plants Climate Adaptation Partnership (2012):  National Fish, Wildlife, and Plants Climate Adaptation Strategy . Association of Fish and Wildlife Agencies, Council on Environmental Quality, Great Lakes Indian Fish and Wildlife Commission, National Oceanic and Atmospheric Administration, and U.S. Fish and Wildlife Service. Washington, D.C. DOI: 10.3996/082012-FWSReport-1

IPCC (2019). Summary for Policymakers. In: IPCC Special Report on the Ocean and Cryosphere in a Changing Climate. [H.-O. Pörtner, D.C. Roberts, V. Masson-Delmotte, P. Zhai, M. Tignor, E. Poloczanska, K. Mintenbeck, A. Alegría, M. Nicolai, A. Okem, J. Petzold, B. Rama, N.M. Weyer (eds.)]. In press.

NASA JPL: "Consensus: 97% of climate scientists agree."  Global Climate Change . A website at NASA's Jet Propulsion Laboratory (climate.nasa.gov/scientific-consensus). (Accessed July 2013.)

We value your feedback

Help us improve our content

An official website of the United States government

Here’s how you know

Official websites use .gov A .gov website belongs to an official government organization in the United States.

Secure .gov websites use HTTPS A lock ( Lock A locked padlock ) or https:// means you’ve safely connected to the .gov website. Share sensitive information only on official, secure websites.

JavaScript appears to be disabled on this computer. Please click here to see any active alerts .

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

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

The Basics of Climate Change

Greenhouse gases affect Earth’s energy balance and climate

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

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

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

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

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

Human activities have added greenhouse gases to the atmosphere

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

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

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

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

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

Climate records show a warming trend

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

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

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

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

Many complex processes shape our climate

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

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

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

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

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

Human activities are changing the climate

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

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

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

How will climate change in the future?

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

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

Climate change and biodiversity

Human activities are changing the climate. Science can help us understand what we are doing to habitats and the climate, but also find solutions.

Email updates

We promote excellence in science so that, together, we can benefit humanity and tackle the biggest challenges of our time.

Subscribe to our newsletters to be updated with the latest news on innovation, events, articles and reports.

What subscription are you interested in receiving? (Choose at least one subject)

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

Discover More Topics From NASA

Explore Earth Science

Earth Science in Action

Earth Science Data

Facts About Earth

Our Science Emergency Fund is now LIVE. Your gift is urgently needed!

How Do We Know that Humans Are the Major Cause of Global Warming?

Published Jul 14, 2009 Updated Jan 21, 2021

Humans cause climate change. How do we know?

Scientists agree that global warming is caused mainly by human activity. Specifically, the evidence shows that certain heat-trapping gases, such as carbon dioxide, are warming the world—and that we release those gases when we burn fossil fuels like coal, oil, and gas.

As scientific models and methods grow more sophisticated, and as we collect more data, our confidence in human-caused climate change only grows higher. Here’s what we know.

Climate science 101

Climate science encompasses a range of disciplines, from oceanography and meteorology, to chemistry, physics, biology and computer science.

Generally speaking, scientists working on climate change compare the climate patterns they observe with patterns developed using sophisticated models of Earth's systems (such as the atmosphere and ocean). By comparing the observed and modeled patterns, scientists can positively identify " human fingerprints ” and attribute a proportion of observed warming to human activities.

These fingerprints are found in a diverse range of records from the atmosphere, the ocean, and Earth’s surface. They include rising levels of carbon dioxide, unprecedented warming, and a distinct atomic signature left behind in the atmosphere when fossil fuels are burned.

Rising carbon dioxide levels

Carbon dioxide (CO 2 ) is the heat-trapping gas in our atmosphere responsible for most of the warming measured over the past several decades. It’s released during cement manufacturing and when coal, gas, and oil are burned—something humans started doing a great deal of during the Industrial Revolution through to today.

The concentration of CO 2 in the Earth’s atmosphere has increased dramatically over the last 150 years, from a pre-industrial era concentration of approximately 280 parts per million (ppm) to more than 410 ppm currently. CO 2 concentration levels are unlikely to dip below these annual averages for hundreds of years .

In fact, measurements from ancient ice cores show that CO 2 is now at its highest levels in over 800,000 years.

Unprecedented warming

As the concentration of CO 2 and other heat-trapping gases in the atmosphere rises, the Earth warms up. In fact, Earth has recently undergone unprecedented warming , particularly since the 1950s.

Every single year since 1977 has been warmer than the 20th century average. Nineteen of the 20 warmest years have occurred since 2001. The period of 2015 to 2019 included the top five hottest years on record .

Analysis of these trends strongly suggests that without the emissions from burning coal and oil, it is very unlikely that 13 out of the 15 warmest years on record would have occurred either on their own or in such quick succession. This also makes sense from the known causes.

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. 2018 US National Climate Assessment

Fossil fuel fingerprinting

We know that CO 2 warms the world, that CO 2 concentrations are at record-breaking levels, and that global temperatures are rising. But how do we know for certain that humans are the cause?

The answer is in the science. The CO 2 produced from fossil fuels carries a unique signature that differentiates it from CO 2 produced from other sources. In brief, it carries a specific ratio of carbon isotopes that is only found in the atmosphere when coal, oil, or gas is burned.

Scientists call this δ 13 C (pronounced "delta C thirteen"), and it’s a smoking gun. Since the 1880s, δ 13 C has changed in a way that could only happen if CO 2 was increasingly coming from fossil fuel sources.

This information tells scientists that human-caused fossil fuel emissions have been the main contributor to the rise in CO 2 concentrations since the pre-industrial era.

The scientific consensus

Within the scientific community, there is essentially no disagreement on the causes of climate change. Multiple studies have shown that at least 97 percent of scientists agree that global warming is happening and that human activity is the primary cause.

Major scientific assessments also agree. The 2018 US National Climate Assessment —whose authors include 300 leading scientists and thirteen federal government agencies—concludes that “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.”

Similarly, an authoritative 2014 report by the Intergovernmental Panel on Climate Change, written and reviewed by hundreds of climate experts and scientists from countries around the world, 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.”

Natural factors

We know that warming and cooling have happened in the past , long before humans were around. Natural “climate drivers” include the energy from the sun; aerosols from periodic volcanic eruptions, dust, and salt spray; natural ecological phenomena like methane-emitting termite mounds and CO 2 uptake by plants; and variations in snow and ice cover that change how much the Earth’s surface reflects the sun’s energy back into space (referred to as albedo).

All of these factors have profoundly shaped the Earth’s climate. However, none of them sufficiently explain the recent, dramatic increase in global temperatures. For that, scientists need to include human influences.

Natural drivers + human drivers best match reality

When natural and human-induced climate drivers are compared to one another, the human influences are so large that they crowd out other climate drivers over the past half century, producing the warming that we’re all experiencing. Put another way, when climate scientists focus only on natural climate drivers, their models cannot accurately reproduce the observed warming of the past half century. But when the models also include human-induced climate drivers, they accurately capture recent temperature increases in the atmosphere and in the oceans.

In fact, studies show that human activity is responsible for more than half of the warming observed since 1951.

This evidence has led organizations like the IPCC to conclude that the effects of heat-trapping gases and other human activities are both detectable throughout the climate system and “extremely likely to have been the dominant cause of the observed warming since the mid-20th century.”

Are humans contributing to more extreme weather?

In recent years, the field of attribution science has become more sophisticated, and scientists are now able to quantify how much more likely an extreme event—such as a heat wave or a massive downpour—was as a result of human-caused climate change.

For example, in a landmark 2004 paper , researchers determined that climate change had at least doubled the risk of occurrence of the record-breaking 2003 European summer heat wave, which resulted in the deaths of tens of thousands of people. A 2016 study of the same heat wave concluded that human-caused climate change had increased the risk of heat-related mortality during the event by about 70 percent in central Paris and about 20 percent in London.

Similarly, researchers found that the record-breaking precipitation Texas experienced in 2017 during Hurricane Harvey was made three times more likely and 15 percent more intense by climate change.

More recently, scientists have found that fingerprinting of climate change can be detected in global daily weather patterns since 2012 and yearly patterns since 1999.

While some types of events are more readily attributable to global warming than others, attribution science is becoming increasingly robust. Several authoritative scientific institutions and government agencies have confirmed both the rigor and the validity of attributing individual extreme events to human-caused climate change.

We are the cause, and we are the solution

Knowing that human activities are the main driver of global warming helps us understand how and why our climate is changing, and it clearly defines the problem as one that is within our power to address.

We cannot avoid some level of warming caused by the heat-trapping gases already present in the atmosphere. Some of the gases (such as carbon dioxide and nitrous oxide) will last for more than a century. Many of the people who have contributed the least to global warming—including much of the Global South, and marginalized and low-income communities across the world—are facing the most severe impacts.

But with aggressive measures to reduce future emissions and adapt to those climate impacts we cannot avoid, we have a small window to avoid the worst climate change harms and build a better world.

What does that mean? It means investing in a clean energy economy and healthier and more livable and resilient communities. It means transforming transportation , reorienting our food system , and shifting to lower-carbon lifestyles. It means battling the disinformation spread by fossil fuel companies and other wealthy interests. And it means fighting for equity and environmental justice for all.

The Paris Agreement of 2015 called on nations to keep global warming under the dangerous threshold of 2°C, aiming for 1.5°C. In recent years, the global climate movement—and young people in particular—have been demanding we do even better. With the right policies, practices, vision and cooperation, acting boldly now will give us the best chance of creating the safe and promising future the youth of the world deserve.

Related resources

Water, Water Every Where

Looming Deadlines for Coastal Resilience

Follow the Money

Attacks on Science

We use cookies to improve your experience. By continuing, you accept our use of cookies. Learn more .

Support our work

Other ways to give.

• Honor & memory
• Become a member
• Give monthly
• Make a planned gift
• Gift memberships

Your donation at work

• History & Society
• Science & Tech
• Biographies
• Animals & Nature
• Geography & Travel
• Arts & Culture
• Games & Quizzes
• On This Day
• One Good Fact
• New Articles
• Lifestyles & Social Issues
• Philosophy & Religion
• Politics, Law & Government
• World History
• Health & Medicine
• Browse Biographies
• Birds, Reptiles & Other Vertebrates
• Bugs, Mollusks & Other Invertebrates
• Environment
• Fossils & Geologic Time
• Entertainment & Pop Culture
• Sports & Recreation
• Visual Arts
• Demystified
• Image Galleries
• Infographics
• Top Questions
• Britannica Kids
• Saving Earth
• Space Next 50
• Student Center
• Introduction
• The Earth system

Evidence for climate change

Solar variability, volcanic activity, tectonic activity.

• Orbital (Milankovich) variations
• Greenhouse gases
• Human activities
• Seasonal variation
• Interannual variation
• Decadal variation
• Centennial-scale variation
• Thermal maxima
• ENSO variation in the Holocene
• Amplification of the Indian Ocean monsoon
• The most recent glacial phase
• The Last Glacial Maximum
• The last deglaciation
• Climate change and the emergence of agriculture
• Glacial and interglacial cycles of the Pleistocene
• The last great cooling
• Cenozoic climates
• Phanerozoic climates
• Faint young Sun paradox
• Photosynthesis and atmospheric chemistry
• Snowball Earth hypothesis
• Abrupt climate changes in Earth history

• Who is Al Gore?
• Should the United States use the Electoral College in presidential elections so that candidates such as George W. Bush may win over popular vote winners like Al Gore?
• How does global warming work?
• Where does global warming occur in the atmosphere?
• Why is global warming a social problem?

Our editors will review what you’ve submitted and determine whether to revise the article.

• Penn State Institute of Energy and the Environment - Growing Impact: Contrails and climate change
• The Royal Society - The Basics of Climate Change
• Global Footprint Network - Climate Change: Carbon Footprint
• Australian Academy of Science - What Is Climate Change?
• Carnegie Endowment for International Peace - Economic Development in an Era of Climate Change
• CALS Encyclopedia of Arkansas - Climate Change
• National Geographic Kids - What is Climate Change?
• Natural Resources Defense Council - What is Climate Change?
• Environmental Protection Agency - What is Climate Change?
• Environmental and Energy Study Institute - Climate Change
• Biology LibreTexts - Implications of Climate Change
• climate change - Children's Encyclopedia (Ages 8-11)
• climate change - Student Encyclopedia (Ages 11 and up)
• Table Of Contents

All historical sciences share a problem: As they probe farther back in time, they become more reliant on fragmentary and indirect evidence. Earth system history is no exception. High-quality instrumental records spanning the past century exist for most parts of the world, but the records become sparse in the 19th century, and few records predate the late 18th century. Other historical documents, including ship’s logs, diaries, court and church records, and tax rolls, can sometimes be used. Within strict geographic contexts , these sources can provide information on frosts , droughts , floods , sea ice , the dates of monsoons , and other climatic features—in some cases up to several hundred years ago.

Recent News

Fortunately, climatic change also leaves a variety of signatures in the natural world. Climate influences the growth of trees and corals , the abundance and geographic distribution of plant and animal species, the chemistry of oceans and lakes , the accumulation of ice in cold regions, and the erosion and deposition of materials on Earth’s surface. Paleoclimatologists study the traces of these effects, devising clever and subtle ways to obtain information about past climates. Most of the evidence of past climatic change is circumstantial, so paleoclimatology involves a great deal of investigative work. Wherever possible, paleoclimatologists try to use multiple lines of evidence to cross-check their conclusions. They are frequently confronted with conflicting evidence, but this, as in other sciences, usually leads to an enhanced understanding of the Earth system and its complex history. New sources of data, analytical tools, and instruments are becoming available, and the field is moving quickly. Revolutionary changes in the understanding of Earth’s climate history have occurred since the 1990s, and coming decades will bring many new insights and interpretations.

Ongoing climatic changes are being monitored by networks of sensors in space, on the land surface, and both on and below the surface of the world’s oceans. Climatic changes of the past 200–300 years, especially since the early 1900s, are documented by instrumental records and other archives. These written documents and records provide information about climate change in some locations for the past few hundred years. Some very rare records date back over 1,000 years. Researchers studying climatic changes predating the instrumental record rely increasingly on natural archives, which are biological or geologic processes that record some aspect of past climate. These natural archives, often referred to as proxy evidence, are extraordinarily diverse; they include, but are not limited to, fossil records of past plant and animal distributions, sedimentary and geochemical indicators of former conditions of oceans and continents, and land surface features characteristic of past climates. Paleoclimatologists study these natural archives by collecting cores, or cylindrical samples, of sediments from lakes, bogs , and oceans; by studying surface features and geological strata; by examining tree ring patterns from cores or sections of living and dead trees; by drilling into marine corals and cave stalagmites ; by drilling into the ice sheets of Antarctica and Greenland and the high-elevation glaciers of the Plateau of Tibet , the Andes , and other montane regions; and by a wide variety of other means. Techniques for extracting paleoclimatic information are continually being developed and refined, and new kinds of natural archives are being recognized and exploited.

Causes of climate change

It is much easier to document the evidence of climate variability and past climate change than it is to determine their underlying mechanisms. Climate is influenced by a multitude of factors that operate at timescales ranging from hours to hundreds of millions of years. Many of the causes of climate change are external to the Earth system. Others are part of the Earth system but external to the atmosphere . Still others involve interactions between the atmosphere and other components of the Earth system and are collectively described as feedbacks within the Earth system. Feedbacks are among the most recently discovered and challenging causal factors to study. Nevertheless, these factors are increasingly recognized as playing fundamental roles in climate variation. The most important mechanisms are described in this section.

The luminosity, or brightness, of the Sun has been increasing steadily since its formation. This phenomenon is important to Earth’s climate, because the Sun provides the energy to drive atmospheric circulation and constitutes the input for Earth’s heat budget. Low solar luminosity during Precambrian time underlies the faint young Sun paradox , described in the section Climates of early Earth .

Radiative energy from the Sun is variable at very small timescales, owing to solar storms and other disturbances, but variations in solar activity, particularly the frequency of sunspots , are also documented at decadal to millennial timescales and probably occur at longer timescales as well. The “ Maunder minimum ,” a period of drastically reduced sunspot activity between 1645 and 1715, has been suggested as a contributing factor to the Little Ice Age . ( See below Climatic variation and change since the emergence of civilization .)

Volcanic activity can influence climate in a number of ways at different timescales. Individual volcanic eruptions can release large quantities of sulfur dioxide and other aerosols into the stratosphere , reducing atmospheric transparency and thus the amount of solar radiation reaching Earth’s surface and troposphere . A recent example is the 1991 eruption in the Philippines of Mount Pinatubo , which had measurable influences on atmospheric circulation and heat budgets. The 1815 eruption of Mount Tambora on the island of Sumbawa had more dramatic consequences, as the spring and summer of the following year (1816, known as “the year without a summer”) were unusually cold over much of the world. New England and Europe experienced snowfalls and frosts throughout the summer of 1816.

Volcanoes and related phenomena, such as ocean rifting and subduction, release carbon dioxide into both the oceans and the atmosphere. Emissions are low; even a massive volcanic eruption such as Mount Pinatubo releases only a fraction of the carbon dioxide emitted by fossil-fuel combustion in a year. At geologic timescales, however, release of this greenhouse gas can have important effects. Variations in carbon dioxide release by volcanoes and ocean rifts over millions of years can alter the chemistry of the atmosphere. Such changeability in carbon dioxide concentrations probably accounts for much of the climatic variation that has taken place during the Phanerozoic Eon . ( See below Phanerozoic climates .)

Tectonic movements of Earth’s crust have had profound effects on climate at timescales of millions to tens of millions of years. These movements have changed the shape, size, position, and elevation of the continental masses as well as the bathymetry of the oceans. Topographic and bathymetric changes in turn have had strong effects on the circulation of both the atmosphere and the oceans . For example, the uplift of the Tibetan Plateau during the Cenozoic Era affected atmospheric circulation patterns, creating the South Asian monsoon and influencing climate over much of the rest of Asia and neighbouring regions.

Tectonic activity also influences atmospheric chemistry, particularly carbon dioxide concentrations. Carbon dioxide is emitted from volcanoes and vents in rift zones and subduction zones . Variations in the rate of spreading in rift zones and the degree of volcanic activity near plate margins have influenced atmospheric carbon dioxide concentrations throughout Earth’s history. Even the chemical weathering of rock constitutes an important sink for carbon dioxide. (A carbon sink is any process that removes carbon dioxide from the atmosphere by the chemical conversion of CO 2 to organic or inorganic carbon compounds.) Carbonic acid, formed from carbon dioxide and water , is a reactant in dissolution of silicates and other minerals. Weathering rates are related to the mass, elevation, and exposure of bedrock . Tectonic uplift can increase all these factors and thus lead to increased weathering and carbon dioxide absorption. For example, the chemical weathering of the rising Tibetan Plateau may have played an important role in depleting the atmosphere of carbon dioxide during a global cooling period in the late Cenozoic Era. ( See below Cenozoic climates .)

Orbital ( Milankovich ) variations

The orbital geometry of Earth is affected in predictable ways by the gravitational influences of other planets in the solar system . Three primary features of Earth’s orbit are affected, each in a cyclic, or regularly recurring, manner. First, the shape of Earth’s orbit around the Sun , varies from nearly circular to elliptical (eccentric), with periodicities of 100,000 and 413,000 years. Second, the tilt of Earth’s axis with respect to the Sun, which is primarily responsible for Earth’s seasonal climates, varies between 22.1° and 24.5° from the plane of Earth’s rotation around the Sun. This variation occurs on a cycle of 41,000 years. In general, the greater the tilt, the greater the solar radiation received by hemispheres in summer and the less received in winter . The third cyclic change to Earth’s orbital geometry results from two combined phenomena: (1) Earth’s axis of rotation wobbles, changing the direction of the axis with respect to the Sun, and (2) the orientation of Earth’s orbital ellipse rotates slowly. These two processes create a 26,000-year cycle, called precession of the equinoxes , in which the position of Earth at the equinoxes and solstices changes. Today Earth is closest to the Sun (perihelion) near the December solstice, whereas 9,000 years ago perihelion occurred near the June solstice.

These orbital variations cause changes in the latitudinal and seasonal distribution of solar radiation, which in turn drive a number of climate variations. Orbital variations play major roles in pacing glacial-interglacial and monsoonal patterns. Their influences have been identified in climatic changes over much of the Phanerozoic. For example, cyclothems —which are interbedded marine, fluvial, and coal beds characteristic of the Pennsylvanian Subperiod (323.2 million to 298.9 million years ago)—appear to represent Milankovitch-driven changes in mean sea level .

How does the climate system work?

Greenhouse gases and the greenhouse effect

Some gases in the Earth's atmosphere trap heat and stop it escaping into space. We call these ' greenhouse gases '. These gases act as a warming blanket around the Earth, known as the 'greenhouse effect'.

Greenhouse gases come from both human and natural sources. Gases like carbon dioxide, methane, and nitrous oxide naturally occur in the atmosphere. Others, such as chlorofluorocarbons (CFCs), are only produced by human activity.

When short-wave radiation from the sun reaches Earth, most of it passes straight through and hits the surface. The Earth absorbs most of this radiation and gives off longer-wavelength infrared radiation.

The greenhouse gases absorb some of this infrared radiation, instead of it passing straight out into space. The atmosphere then emits radiation in all directions, sending some of it back to the surface, causing the planet to heat up. This process is known as the 'greenhouse effect'.

The greenhouse effect is critical to our survival. In fact, without greenhouse gases, Earth would be about 30 degrees colder than it is today. Without greenhouse gases and their warming effect, we wouldn't be able to survive.

However, since the Industrial Revolution, we've been adding more and more greenhouse gases into the air, trapping even more heat. Instead of keeping Earth at a warm, stable temperature, the greenhouse effect is heating the planet at a much faster rate. We call this the 'enhanced greenhouse effect' and it's the main cause of climate change.

Human causes of climate change

Humans cause climate change by releasing carbon dioxide and other greenhouse gases into the air. Today, there is more carbon dioxide in the atmosphere than there ever has been in at least the past 2 million years. During the 20th and 21st century, the level of carbon dioxide rose by 40%.

We produce greenhouse gases in lots of different ways:

• Burning fossil fuels – Fossil fuels such as oil, gas, and coal contain carbon dioxide that has been 'locked away' in the ground for thousands of years. When we take these out of the land and burn them, we release the stored carbon dioxide into the air.
• Deforestation – Forests remove and store carbon dioxide from the atmosphere. Cutting them down means that carbon dioxide builds up quicker since there are no trees to absorb it. Not only that, trees release the carbon they stored when we burn them.
• Agriculture – Planting crops and rearing animals releases many different types of greenhouse gases into the air. For example, animals produce methane, which is 30 times more powerful than carbon dioxide as a greenhouse gas. The nitrous oxide used for fertilisers is ten times worse and is nearly 300 times more potent than carbon dioxide!
• Cement – Producing cement is another contributor to climate change, causing 2% of our entire carbon dioxide emissions.

Natural changes to the climate

The leading cause of climate change is human activity and the release of greenhouse gases. However, there are lots of natural causes that also lead to changes in the climate system.

Natural cycles can cause the climate to alternate between warming and cooling. There are also natural factors that force the climate to change, known as 'forcings'. Even though these natural causes contribute to climate change, we know that they are not the primary cause, based on scientific evidence .

Some of these natural cycles include:

• Milankovitch cycles – As Earth travels around the sun, its path and the tilt of its axis can change slightly. These changes, called Milankovitch cycles, affect the amount of sunlight that falls on Earth. This can cause the temperature of Earth to change. However, these cycles take place over tens or hundreds of thousands of years and are unlikely to be causing the changes to the climate that we are seeing today.
• El Niño Southern Oscillation (ENSO) – ENSO is a pattern of changing water temperatures in the Pacific Ocean. In an 'El Niño' year, the global temperature warms up, and in a 'La Niña' year, it cools down. These patterns can affect the global temperature for a short amount of time (months or years) but cannot explain the persistent warming that we see today.

What is El Niño, what does it mean and how does it affect weather around the world?

Natural forcings that can contribute to climate change include:

• Solar irradiance – Changing energy from the sun has affected the temperature of Earth in the past. However, we have not seen anything strong enough to change our climate. Any increase in solar energy would make the entire atmosphere of Earth warm, but we can only see warming in the bottom layer.
• Volcanic eruptions – Volcanoes have a mixed effect on our climate. Eruptions produce aerosol particles that cool Earth, but they also release carbon dioxide, which warms it. Volcanoes produce 50 times less carbon dioxide than humans do, so we know they are not the leading cause of global warming. On top of this, cooling is the dominant effect of volcanic eruptions, not warming.

Are humans responsible for climate change?

When looking at all the evidence, there is a large scientific consensus that humans are the leading cause of climate change. In their latest report, the Intergovernmental Panel on Climate Change stated unequivocally that human activity is the cause of global warming.

Natural climate cycles can change the temperature of Earth, but the changes we are seeing are happening at a scale and speed that natural cycles cannot explain. These cycles affect the global temperature for years, or sometimes just months, not the 100 years that we have observed. Meanwhile, longer-term changes like Milankovitch cycles and solar irradiance take thousands and thousands of years.

There are lots of things that affect climate change, but the evidence is irrefutable. Human activity, such as burning fossil fuels and changing how we use the land, is the leading cause of climate change.

Stay up to date with the latest climate news

Our climate newsletter shares research and news to give you the latest updates on climate science. We publish the newsletter twice a month and it's easy to sign up.

Find out more and sign up to the climate newsletter.

Related links

• What is climate change?
• Effects of climate change
• Greenhouse gases
• Climate change questions
• Climate science
• Organisations and reports
• Climate newsletter
• Natural climate variability
• Tackling climate misinformation

Help us improve our website

ENCYCLOPEDIC ENTRY

Climate change.

Climate change is a long-term shift in global or regional climate patterns. Often climate change refers specifically to the rise in global temperatures from the mid-20th century to present.

Earth Science, Climatology

Fracking tower

Fracking is a controversial form of drilling that uses high-pressure liquid to create cracks in underground shale to extract natural gas and petroleum. Carbon emissions from fossils fuels like these have been linked to global warming and climate change.

Photograph by Mark Thiessen / National Geographic

Learning materials

Upcoming event.

• Explorer Classroom: Photographing the Frozen Frontier with Esther Horvath | December 5

Climate is sometimes mistaken for weather. But climate is different from weather because it is measured over a long period of time, whereas weather can change from day to day, or from year to year. The climate of an area includes seasonal temperature and rainfall averages, and wind patterns. Different places have different climates. A desert, for example, is referred to as an arid climate because little water falls, as rain or snow, during the year. Other types of climate include tropical climates, which are hot and humid , and temperate climates, which have warm summers and cooler winters.

Climate change is the long-term alteration of temperature and typical weather patterns in a place. Climate change could refer to a particular location or the planet as a whole. Climate change may cause weather patterns to be less predictable. These unexpected weather patterns can make it difficult to maintain and grow crops in regions that rely on farming because expected temperature and rainfall levels can no longer be relied on. Climate change has also been connected with other damaging weather events such as more frequent and more intense hurricanes, floods, downpours, and winter storms.

In polar regions, the warming global temperatures associated with climate change have meant ice sheets and glaciers are melting at an accelerated rate from season to season. This contributes to sea levels rising in different regions of the planet. Together with expanding ocean waters due to rising temperatures, the resulting rise in sea level has begun to damage coastlines as a result of increased flooding and erosion.

The cause of current climate change is largely human activity, like burning fossil fuels , like natural gas, oil, and coal. Burning these materials releases what are called greenhouse gases into Earth’s atmosphere . There, these gases trap heat from the sun’s rays inside the atmosphere causing Earth’s average temperature to rise. This rise in the planet's temperature is called global warming. The warming of the planet impacts local and regional climates. Throughout Earth's history, climate has continually changed. When occuring naturally, this is a slow process that has taken place over hundreds and thousands of years. The human influenced climate change that is happening now is occuring at a much faster rate.

Media Credits

The audio, illustrations, photos, and videos are credited beneath the media asset, except for promotional images, which generally link to another page that contains the media credit. The Rights Holder for media is the person or group credited.

Production Managers

Program specialists, last updated.

August 29, 2024

User Permissions

For information on user permissions, please read our Terms of Service. If you have questions about how to cite anything on our website in your project or classroom presentation, please contact your teacher. They will best know the preferred format. When you reach out to them, you will need the page title, URL, and the date you accessed the resource.

If a media asset is downloadable, a download button appears in the corner of the media viewer. If no button appears, you cannot download or save the media.

Text on this page is printable and can be used according to our Terms of Service .

Interactives

Any interactives on this page can only be played while you are visiting our website. You cannot download interactives.

Related Resources

• Share full article

The Science of Climate Change Explained: Facts, Evidence and Proof

Definitive answers to the big questions.

Credit... Photo Illustration by Andrea D'Aquino

Supported by

By Julia Rosen

Ms. Rosen is a journalist with a Ph.D. in geology. Her research involved studying ice cores from Greenland and Antarctica to understand past climate changes.

• Published April 19, 2021 Updated Nov. 6, 2021

The science of climate change is more solid and widely agreed upon than you might think. But the scope of the topic, as well as rampant disinformation, can make it hard to separate fact from fiction. Here, we’ve done our best to present you with not only the most accurate scientific information, but also an explanation of how we know it.

How do we know climate change is really happening?

• How much agreement is there among scientists about climate change?
• Do we really only have 150 years of climate data? How is that enough to tell us about centuries of change?
• How do we know climate change is caused by humans?
• Since greenhouse gases occur naturally, how do we know they’re causing Earth’s temperature to rise?
• Why should we be worried that the planet has warmed 2°F since the 1800s?
• Is climate change a part of the planet’s natural warming and cooling cycles?
• How do we know global warming is not because of the sun or volcanoes?
• How can winters and certain places be getting colder if the planet is warming?
• Wildfires and bad weather have always happened. How do we know there’s a connection to climate change?
• How bad are the effects of climate change going to be?
• What will it cost to do something about climate change, versus doing nothing?

Climate change is often cast as a prediction made by complicated computer models. But the scientific basis for climate change is much broader, and models are actually only one part of it (and, for what it’s worth, they’re surprisingly accurate ).

For more than a century , scientists have understood the basic physics behind why greenhouse gases like carbon dioxide cause warming. These gases make up just a small fraction of the atmosphere but exert outsized control on Earth’s climate by trapping some of the planet’s heat before it escapes into space. This greenhouse effect is important: It’s why a planet so far from the sun has liquid water and life!

However, during the Industrial Revolution, people started burning coal and other fossil fuels to power factories, smelters and steam engines, which added more greenhouse gases to the atmosphere. Ever since, human activities have been heating the planet.

Where it was cooler or warmer in 2020 compared with the middle of the 20th century

Global average temperature compared with the middle of the 20th century

+0.75°C

–0.25°

30 billion metric tons

Carbon dioxide emitted worldwide 1850-2017

Rest of world

Other developed

European Union

Developed economies

Other countries

United States

E.U. and U.K.

We are having trouble retrieving the article content.

Please enable JavaScript in your browser settings.

Thank you for your patience while we verify access. If you are in Reader mode please exit and  log into  your Times account, or  subscribe  for all of The Times.

Thank you for your patience while we verify access.

Already a subscriber?  Log in .

Want all of The Times?  Subscribe .

Advertisement

The climate is changing, but not just because of humans. Here's why that matters.

The climate is changing — the thing is, it isn’t just due to humans.

Natural forces beyond human control are also gradually affecting our climate. These geophysical forces are vital to understanding global warming. Man is indeed responsible for a large portion — possibly even a majority — of global warming. But also in play are complex gravitational interactions, including changes in the Earth’s orbit, axial tilt and torque.

This fact needs to be included in the public debate. Because these gravitational shifts, occurring over millennia, can influence climate patterns and ultimately lead to noticeable variations in seasons. Interestingly, research suggests climate change can alter the tilt of the Earth, but an unrelated change in tilt can also further change the climate. It is a balance-counterbalance relationship.

Changes in the Earth’s path around the Sun, or eccentricity, involve shifts in the orbit around the Sun from a roughly circular journey to more of an elliptical one . When the Earth gradually adopts a more elliptical orbit, there are more pronounced temperatures during the summer and winter months. This alteration is exacerbated when the Earth’s axial tilt is inclined to a sharper degree than usual. As this happens, it causes the North and South Poles to be positioned more directly toward the Sun.

Haven’t you noticed the recent rise in irregular weather patterns? This is not just a man-made problem. Gradual slight variations in the Earth’s orbit around the Sun can strongly influence temperature extremes. This is important because the conversation around climate change has become so politicized, we've totally lost sight of the science — and with it, any room for bipartisanship.

Tropical storms, for example, have been forming later in what we know as hurricane season. Based on my own analysis, over the past three decades, the majority of Category 3 or stronger storms to hit the United States appear from late August to early October. Earlier in the 20th century, storms usually occurred in June, July and early August.

It doesn’t stop there. Changes in seasons can also affect other types of storms, including severe winter snowstorms and tornadoes. Recall the Storm of the Century in 1993 on the heels of Hurricane Andrew the year prior. Or what about the recent string of snowstorms (with names like Snowpocalypse, Snowmageddon and Snowzilla) dovetailing with warm-weather superstorms. Climate extremes are evident, and not just with hurricanes.

The variations in the Earth’s orbit are known as the Milankovitch cycles — after the Serbian geophysicist Milutin Milanković, who hypothesized this phenomenon in the 1920s. He discovered that variations in the Earth’s path around the Sun, axial tilt and torque could together affect our climate.

Even a slight change or orientation in the precession of the Earth’s rotating body can cause a wobbling effect shifting torque in different areas since the planet is not a perfect sphere to some people’s surprise.

Now would seem a particularly apt time to act. The 2017 Atlantic hurricane season was an intense, record-setting period . With several landfall hurricanes — Harvey, Irma, Jose and Maria — barreling their way through the Caribbean and Gulf of Mexico, devastating parts of the Leeward Islands and United States.

Still, even President Donald J. Trump has implied the whole of idea climate change may just be a hoax . Most Republicans seem to agree that it is not a serious problem.

Meanwhile, while some Democrats have tried to use the frequency and intensity of storms in the hopes of highlighting the climate change conversation, even this effort has seemed muted.

To make effective policy, it is important for politicians and activists alike to set aside their ideological differences.

There is now a real opportunity for new legislation, sound environmental legislation. But will we squander this unprecedented opportunity, punting the ball yet again? You can bet on it. Given the realities of everyday life, the extent of social beliefs, political attitudes and economic perspectives vary on a wide range of policy issues.

To make sound and effective policy, it is important for politicians and activists alike to set aside their ideological differences and return to the basics of science, in this case, the mechanics of science. After all, shouldn’t we be relying more heavily upon geoscientists and weather forecasters to provide evidence-based data and predictive modeling?

Risks to disasters are increasing. Population growth along coastlines worldwide, in addition to technological and infrastructural development, will inherently result in a concomitant increase in places prone to disasters. Modern society relies upon government for effective response to and recovery from such events.

Change is occurring and will continue to do so. As the population continues to explode and resources are consumed on a massive scale, trying to stop both is unrealistic. It is more than just being unrealistic, it is simply wasting critical time. I know, science isn’t sexy. The obsession on why storms are occurring in lieu of discussing the how is leading us down a dangerous path. A deadly path.

The heightened culture of disaster only feeds our attention on political banter and ideological semantics with no room for informed decision-making.

We get it, Mother Nature always wins. So, are we now faced with the sobering lesson that little can be done, and we should just throw in the towel? No, of course not. Though climate change is inevitable, we also need to have a healthy appreciation of the fact that climate shifts aren’t just limited to rapidly changing weather patterns.

Turning the corner into unexplored territory is always difficult. By having a broader sense of communal resiliency — social, political and economic standing — we can manage this unavoidable pendulum of climate extremes. With the recent sweeping of storms draining response efforts and budgetary resources, now is the time to set aside the theatrical shenanigans and engage in realpolitik.

Tonya T. Neaves is the director for the Centers on the Public Service at George Mason University’s Schar School of Policy and Government, where she also is a faculty member in its master of public administration program and coordinator for the Emergency Management and Homeland Security certificate.

Tonya T. Neaves is the director for the Centers on the Public Service at George Mason University’s Schar School of Policy and Government, where she also is a faculty member in its master of public administration program and coordinator for the Emergency Management and Homeland Security certificate. 

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.

READ FREE ONLINE

Welcome to OpenBook!

You're looking at OpenBook, NAP.edu's online reading room since 1999. Based on feedback from you, our users, we've made some improvements that make it easier than ever to read thousands of publications on our website.

Do you want to take a quick tour of the OpenBook's features?

Show this book's table of contents , where you can jump to any chapter by name.

...or use these buttons to go back to the previous chapter or skip to the next one.

Jump up to the previous page or down to the next one. Also, you can type in a page number and press Enter to go directly to that page in the book.

Switch between the Original Pages , where you can read the report as it appeared in print, and Text Pages for the web version, where you can highlight and search the text.

To search the entire text of this book, type in your search term here and press Enter .

Share a link to this book page on your preferred social network or via email.

View our suggested citation for this chapter.

Ready to take your reading offline? Click here to buy this book in print or download it as a free PDF, if available.

Get Email Updates

Do you enjoy reading reports from the Academies online for free ? Sign up for email notifications and we'll let you know about new publications in your areas of interest when they're released.

Is the Sun Causing Climate Change?

Does the sun change over time.

Sunlight is the reason we can live on planet Earth. It helps warm up the planet and helps plants make food. Credit: NASA/JPL Caltech

The Sun shines its light on Earth and helps heat our planet. It’s warmth and light make life possible on Earth. Plants need sunlight to create food. As Earth spins, this sunlight gives us day and night. And as Earth goes around the Sun, on a path called an orbit , the sunlight gives us seasons .

The Sun is dynamic, which means that it is always changing. For example, sometimes it has sunspots , or what looks like dark spots on the surface. Sometimes, it doesn’t. NASA scientists who study the Sun can predict when there will be more or less sunspots. That’s because they follow a pattern called the solar cycle .

This picture of the Sun has a few dark-colored spots. Those are sunspots. Credit: NASA

The solar cycle lasts about 11 years. The Sun has times with few or no sunspots. This is called the solar minimum. Then over the next five to six years the number of sunspots increases until it reaches solar maximum. After that, the number of sunspots decreases over the next to six years until it reaches a minimum again. Then the cycle starts over.

These changes in the Sun are known as solar activity. Changes in solar activity over time can change the strength of the sunlight that reaches Earth. The amount of this change is very small compared to all the heat and light that comes from the Sun. This change is far too small to cause the large rise in global temperatures we have seen.

If It’s Not the Sun, What Causes Climate Change?

We are burning coal, gas, and oil to create energy. We use that energy to power lights, cars, buses, planes, homes, and more. Using this kind of energy adds greenhouse gases, like carbon dioxide (CO2), to the air. Credit: NASA/JPL-Caltech

Today’s climate change is mainly caused by things humans do that add greenhouse gases into the air. This includes burning coal, oil, and gas for energy. Greenhouse gases, like carbon dioxide, act as a warming blanket around the planet . When more greenhouse gases are added, it’s like making the blanket thicker. Earth gets warmer.

When we burn fossil fuels, like coal, oil, and gas, for energy, we add greenhouse gases to the air. Greenhouse gases act like a blanket around the planet, warming it. When more greenhouse gases are added, this acts like a thicker blanket and causes Earth’s temperature to rise. Credit: NASA/JPL-Caltech

NASA scientists measure changes to Earth’s temperature and the amount of greenhouse gases to the air using satellites in space and instruments on the ground. From this information, they can see how greenhouse gases and Earth’s temperatures are changing. They have found that both are increasing.

As we add greenhouse gases to the air, it traps heat. That trapped heat causes Earth’s temperature to rise. Satellite measurements from space help us track these changes over time. Credit: NASA/JPL-Caltech

These measurements helped scientists rule out the Sun and other naturally changing things as the cause of recent climate change. They found that human actions are the main cause for today’s climate change.

Essay: To fix climate anxiety (and also climate change), we first have to fix individualism

• Copy Link URL Copied!

How do you cope? I feel the sorrow, the quiet plea for guidance every time someone asks me this question. As an environmental reporter dedicated to helping people make sense of climate change, I know I should have answers. But the truth is, it took me until now to face my own grief.

My heart keeps breaking whenever I meet yet another child struggling with asthma amid orange, smoke-filled skies. I, too, am reeling from the whiplash of extreme drought and extreme rain , and I’m still haunted by the thought of a mother having to call each of her daughters to say goodbye as the homes around her cave to fire.

Each year, as I reflect on my own reporting on the floods that keep getting worse and the toxic pollution building up in all forms of life , I find myself questioning whether I could ever justify bringing my own children into this world. I agonize over the amount of plastic we can’t avoid using and mourn the monarch butterflies that have vanished. With each new heat record shattered, and each new report declaring a code red for humanity , I can’t help but feel like we’re just counting down the days to our own extinction.

In the face of sea level rise, can we reimagine California’s vanishing coastline?

“Climate anxiety” is the term we now use to describe these feelings, but I must confess, I was perplexed when I first heard these words a few years ago. Anger, frustration, helplessness, exhaustion — these are the emotions I come across more often when getting to know the communities bracing for, or recovering from, the devastation of what they’ve long considered home.

Then a college student asked me about climate anxiety. It came up again on social media, and again in personal essays and polls. This paralyzing dread was suddenly the talk of the town — but it has also, very noticeably, remained absent in some circles.

All this has led me to wonder: What, exactly, is climate anxiety? And how should we cope? At first blush, this anxiety seems rooted in a fear that we’ll never go back to normal, that the future we were once promised is now gone. But who this “normal” is even for (and what we’re actually afraid of losing) speaks to a much more complicated question:

Is this anxiety pointing to a deeper responsibility that we all must face — and ultimately, is this anxiety something we can transcend?

For Jade Sasser, whose research on climate emotions has been grounded by her own experiences as a Black woman, these questions sharpened into focus during a research-methods seminar that she was teaching early last year at UC Riverside.

The class — all female, many from low-income immigrant communities — had been a fairly quiet group all quarter, so Sasser was surprised when the room completely erupted after she broached what she thought would be an academic, somewhat dispassionate discussion about climate change and the future.

Every student was suddenly talking, even yelling, over one another. Thought after thought tumbled out as they shared that not only does the future feel bleak when it comes to the job market, the housing crisis and whether their generation will ever be able to “settle down with kids” — but all this is many times worse when you’re not white, not documented and not born into a college-educated family.

How can they feel hopeful about the future, they asked, when, on top of everything already stacked against them, they also have to worry about wildfires, extreme heat and air pollution getting out of control?

‘It’s almost shameful to want to have children’

‘Climate Anxiety and the Kid Question’ asks: With American society feeling more socially and politically polarized than ever, is it right to bring another person into the world?

“It was literally a collective meltdown unlike anything I had ever experienced,” said Sasser, whose podcast and book, “ Climate Anxiety and the Kid Question, ” were largely inspired by her students that day. “I understood in that moment that you cannot assume someone does not also experience anxiety simply because their way of talking about it may not be the same as yours.”

It doesn’t help, she added, that many people don’t realize what they’re feeling is climate anxiety because the way we talk about it tends to center the experiences of white and more privileged people — people who have been insulated from oppression and have rarely (until now) had to worry about the safety of their own future.

“For a lot of people, climate anxiety looks a certain way: It looks very scared, it looks very sad, and it looks like a person who is ready, willing and able to talk about it,” Sasser said. “But for those who are experiencing many compounding forms of vulnerability at the same time, you can’t just pick out one part of it and say, ‘Oh, this is what’s causing me to feel this way.’”

A brave first step is to acknowledge privilege — and to support, and perhaps even learn, from those who have had to be resilient long before climate change became so overwhelming.

“For me, this work is a matter of survival,” said Kevin J. Patel, who grew up in South L.A. and has been fighting for climate justice since he was 11. He was contemplative, nodding, when I shared what I learned from Sasser, and he gently added that one privilege many communities don’t have is the ability to turn it off. Not everyone can go on a vacation or take a day to recharge, he said. Even having the time to talk about your sadness can be a luxury.

Feeling climate anxiety? These books offer glimmers of hope — and much-needed wisdom

Patel learned at a young age that not all communities get the same level of care. Growing up with hazy air, in a neighborhood hemmed in by the 10 and 110 freeways, Patel almost collapsed one day in front of his sixth-grade class when his heart suddenly started pounding at more than 300 beats per minute.

His parents, farmers from Gujarat, India, rushed Patel to the emergency room and held his hand while everyone around him thought he was dying. After months of hospital visits and procedures, doctors determined that he had developed a severe heart condition in large part due to the smog.

‘For me, this work is a matter of survival.’

— Kevin J. Patel

As he learned to live with an irregular heartbeat, he found joy in his family’s tiny garden and marveled at all the ladybugs that gathered on the tulsi, a special type of basil. He taught his classmates that food came from the ground, not the grocery store, and together, they went on to form an environmental club.

Today, Patel speaks with the hardened wisdom of someone who has experienced much more than the typical 23-year-old. He’s constantly doing something — whether it’s supporting a neighbor, getting water bottle refill stations installed at his school, or turning the idea of a Los Angeles County Youth Climate Commission into reality. For years, he has guided other marginalized youth through OneUpAction , a grassroots environmental group that he built from the ground up.

Even if he doesn’t call it anxiety, he admits he sometimes has trouble focusing, and there’s a tenseness in his body that can be hard to shake off. But he’s usually able to turn it around by talking to his friends or elders, or by reciting his favorite proverb:

They tried to bury us, but they didn’t know we were seeds.

“It’s not about what I need, it’s about what my community needs,” he said. “There is joy in caring for one another. There is joy in coming together to fight for a future that we believe in.”

When talking about climate anxiety, it’s important to differentiate whether you’re assessing these emotions as a mental health condition, or as a cultural phenomenon.

Let’s start with mental health: Polls show climate anxiety is on the rise and that people all around the world are losing sleep over climate change. Organizations like the Climate-Aware Therapist Directory and the American Psychiatric Assn. have put together an increasing number of guides and resources to help more people understand how climate change has affected our emotional well-being.

Poll shows Californians’ climate anxiety is on the rise

Just knowing that climate change is getting worse can trigger serious psychological responses. And the shock and trauma are all the more great if you’ve already had to live through the kinds of disasters that keep the rest of us up at night.

It’s also important to note that social media has magnified our sense of doom. What you see on social media tends to be a particularly intense and cherry-picked version of reality, but studies show that’s exactly how the vast majority of young people are getting their information about climate change: online rather than in school.

But you can’t treat climate anxiety like other forms of anxiety, and here’s where the cultural politics come in: The only way to make climate anxiety go away is to make climate change go away, and given the fraught and deeply systemic underpinnings of climate change, we must also consider this context when it comes to our climate emotions. How we feel is just as much a product of the narratives that have shaped the way we perceive and respond to the world.

“Climate anxiety can’t be limited to just a clinical setting — we have to take it out of the therapy room and look at it through a lens of privilege, and power, and the economic, historical and social structures that are at the root of the problem,” said Sarah Jaquette Ray, whose book “ A Field Guide to Climate Anxiety ” is a call to arms to think more expansively about our despair. “Treating a person’s climate anxiety without challenging these systems only addresses the symptoms, not the causes... and if white or more privileged emotions get the most airtime, and if we don’t see how climate is intersecting with all these other problems, that can result in a greater silencing of the people most impacted.”

Ray, an environmental humanist who chairs the environmental studies program at Cal Poly Humboldt, also emphasized that our distress can actually be a catalyst for much-needed change. These emotions are meant to shake us out of complacency, to sound the alarm to the very real crisis before us. But if we don’t openly talk about climate anxiety as something that is not only normal but also expected, we run the risk of further individualizing the problem. We already have a tendency to shut down and feel alone in our sorrows, which traps us into thinking only about ourselves.

“One huge reason why climate anxiety feels so awful is this feeling of not being able to do anything about it,” Ray said. “But if you actually saw yourself as part of a collective, as interconnected with all these other movements doing meaningful things, you wouldn’t be feeling this despair and loneliness.”

The trick to fixing climate anxiety is to fix individualism, she said. Start small, tap into what you’re already good at, join something bigger than yourself.

And by fixing individualism, as many young activists like Patel have already figured out, we just might have a better shot at fixing climate change.

Let us consider, for a moment, how the words that we use can also limit the way we think about our vulnerability and despair.

Something as simple as the “climate” in “climate anxiety” and how we define “environment” can unintentionally reinforce who we center in the conversation.

“In Nigeria, what we call our environment — it’s not just trees and mountains — it’s also about our food, our jobs, the biodiversity that gives us the life support that we need to thrive every day. That’s what we call our environment; it’s about our people,” said Jennifer Uchendu, who founded SustyVibes , a youth-led sustainability group based in her home country, as well as the Eco-Anxiety in Africa Project , which seeks to validate the emotions and experiences of communities often overlooked in climate conversations. “So if people are being oppressed by the system, it is still linked to our idea of the environment.”

Many of Uchendu’s elders have expressed a lifetime of feeling frustrated and powerless, for example, but she said they didn’t immediately connect these feelings to climate change because “climate anxiety” sounded to them like a new and elite phenomenon.

Editorial: California can make climate polluters pay for the mess they have made of Earth

We hear so often today that climate change is the existential crisis of our time, but that dismisses the trauma and violence to all the people who have been fighting to survive for centuries. Colonization, greed and exploitation are inseparable from climate change, Uchendu said, but we miss these connections when we consider our emotions only through a Western lens.

For Jessa Calderon, a Chumash and Tongva songwriter, these disconnects are ever-present in the concrete-hardened rivers snaking through Los Angeles, and the sour taste of industrialization often singeing the air. In her darkest moments, her heart hurts wondering if her son, Honor, will grow up to know clean water.

Her voice cracked as she recalled a brown bear that had been struck dead on the freeway near the Cajon Pass. As she watched strangers gawk at the limp body and share videos online, she wished she had been able to put the bear to rest and sing him into the spirit world.

“If we don’t see them as our people, then we have no hope for ourselves as a people, because we’re showing that we care about nothing more than ourselves,” she said. “And if we care about nothing more than ourselves, then we’re going to continue to devastate each other and the land.”

It is not too late to turn your climate anxiety into climate empathy. Acknowledging the emotional toll on people beyond yourself can be an opportunity to listen and support one another. Embracing our feelings — and then finding others who also want to turn their fear into action — can be the missing spark to much-needed social and environmental healing.

There is also wisdom to be learned in the songs and traditions of past movements, when people banded together — for civil rights, for women’s suffrage — and found ways to keep hope alive against all odds. And the more we look to the young people still caring for their elders in Nigeria, and to our Indigenous neighbors who continue to sing and love and tend to every living being, the better we might also comprehend the resilience required of all of us in the warming years ahead.

Opinion: Here are the places that could become too hot for humans due to climate change

So how should we cope? For Patel, living with his irregular but unwavering heartbeat, he finds strength in the words of adrienne maree brown, who famously wrote in “ Emergent Strategy ” that in the same way our lives are shaped today by our ancestors, we ourselves are future ancestors. Calderon, who similarly taught her son to leave this Earth better with every passing generation, confided to me that on the days when the sorrow feels too great, she sneaks off to plant native manzanita seeds in neighborhoods stripped of plants and trees.

As I’m reminded of all the love we can still sow for the future, I think of Phoenix Armenta, a longtime climate justice organizer in Oakland who has inspired numerous people, including myself, to take heart in all the times we actually got it right. (Remember acid rain? It was a huge problem, but collective action inspired multiple countries to join forces in the 1980s, and we did what needed to be done.)

“Imagine what kind of world you actually want to live in and start working to make that happen,” said Armenta, who recently made the switch to government planning to help more communities find their voice and determine their own visions for the future.

To grieve the world as we know it is to miss out on opportunities to transform our world for the better. To believe we have nothing left to hope for is a self-fulfilling void. We must find the courage to care, to change, to reimagine the systems that got us into such a devastating crisis in the first place — and we must allow ourselves to dream.

“But it can’t just be my dream, or your dream. It has to be our collective dream,” Armenta said. “I’ve known for a very long time that I can’t save the world, but we can save the world together.”

More to Read

Demanding to be heard

Sept. 15, 2024

What will happen if someone you love has asthma and can’t breathe?

Sometimes we have to escalate to be heard when we’re demanding a livable future

Rosanna Xia is an environment reporter for the Los Angeles Times, where she specializes in stories about the coast and ocean. She was a Pulitzer Prize finalist in 2020 for explanatory reporting, and her award-winning book, “ California Against the Sea ,” has been praised as a poetic and mind-expanding exploration of what we stand to lose in the face of rising water.

More From the Los Angeles Times

Climate & Environment

An oasis where kids learn to be climate literate amid trees, flower beds and herbs

My town became environmentally conscious and so did I

‘Pick up a rake, get dirty, and then you’ll be protecting the land’

Meet the Long Beach student who fought for green schools — and won