Present-day climate change includes global warming, which is the steady rise in Earth's average temperature, and its broader effects on Earth's climate system. Climate change also refers to long-term changes in Earth's climate that have happened in the past. The recent increase in global temperatures is mainly caused by human activities, especially the burning of fossil fuels like coal, oil, and natural gas since the Industrial Revolution. Using fossil fuels, cutting down forests, and certain farming and industrial practices release greenhouse gases. These gases trap heat that Earth sends back into space after absorbing sunlight, which warms the lower atmosphere. Today, Earth's atmosphere has about 50% more carbon dioxide, the main gas causing global warming, than it did at the end of the pre-industrial era. These levels of carbon dioxide have not been seen in millions of years.
Climate change is having a bigger impact on the environment. Deserts are growing larger, and heat waves and wildfires are happening more often. Warming in the Arctic has led to melting permafrost, shrinking glaciers, and less sea ice. Higher temperatures are also causing stronger storms, longer droughts, and more extreme weather. Rapid changes in mountain areas, coral reefs, and the Arctic are forcing many species to move or face extinction. Even if efforts to reduce future warming are successful, some effects will last for centuries. These include warmer oceans, more acidic oceans, and rising sea levels.
Climate change harms people by increasing flooding, extreme heat, and shortages of food and water. It also leads to more diseases and economic losses. Human migration and conflicts can result from these changes. The World Health Organization says climate change is one of the greatest threats to global health in the 21st century. Without action to limit warming, societies and ecosystems will face greater risks. Efforts like building flood barriers or growing drought-resistant crops can help reduce some risks, but some limits to adapting have already been reached. Poorer communities produce a small amount of global emissions but have the least ability to adapt and are most at risk from climate change.
Many effects of climate change have already been observed in the first decades of the 21st century. The year 2024 was the warmest on record, with temperatures 1.60°C (2.88°F) above the average since regular tracking began in 1850. More warming will increase these effects and could trigger tipping points, such as the complete melting of the Greenland ice sheet. Under the 2015 Paris Agreement, countries agreed to keep warming "well under 2°C." However, with current commitments, global warming is expected to reach about 2.8°C (5.0°F) by the end of the century.
There is strong support for taking action on climate change worldwide, and most countries aim to stop emitting carbon dioxide. Fossil fuels can be replaced by stopping their subsidies, using energy more efficiently, and switching to energy sources that do not produce much carbon pollution. These sources include wind, solar, hydro, and nuclear power. Clean electricity can replace fossil fuels for transportation, heating buildings, and industrial processes. Carbon can also be removed from the atmosphere by increasing forest cover and using farming methods that store carbon in soil.
Terminology
Before the 1980s, scientists did not know if the warming caused by more greenhouse gases was stronger than the cooling caused by pollution particles in the air. At that time, they used the term "inadvertent climate modification" to describe how human activities affected the climate. In the 1980s, the terms "global warming" and "climate change" became more common and were often used together. Scientifically, "global warming" only refers to rising average temperatures on Earth's surface, while "climate change" includes both global warming and its effects on Earth's climate, such as changes in rainfall.
The term "climate change" can also describe natural climate changes that have occurred throughout Earth's history. The term "anthropogenic climate change" is sometimes used to describe climate changes caused by human activities.
The term "global warming" was first used in 1975. It became more widely used after NASA scientist James Hansen mentioned it in a 1988 speech to the U.S. Senate. Since the 2000s, the term "climate change" has been used more often. Some scientists, politicians, and media may use terms like "climate crisis," "climate emergency," or "global heating" to describe climate change.
Global temperature rise
Over the last few million years, Earth's climate has gone through cycles of ice ages and warmer periods. One of the warmer times was the Last Interglacial, about 125,000 years ago. During this time, temperatures were 0.5°C to 1.5°C warmer than before global warming began. Sea levels were 5 to 10 meters higher than today. The most recent glacial maximum, 20,000 years ago, was 5–7°C colder. During this time, sea levels were more than 125 meters lower than today.
Temperatures became steady in the current interglacial period, which started 11,700 years ago. This period also marked the beginning of agriculture. Historical changes in temperature, such as the Medieval Warm Period and the Little Ice Age, did not happen at the same time everywhere. In some areas, temperatures may have reached levels similar to the late 20th century. Scientists use climate proxies, like tree rings and ice cores, to study temperatures from that time.
In 1850, thermometer records began to cover the globe. Between the 18th century and 1970, there was little overall warming because the warming from greenhouse gases was balanced by cooling from sulfur dioxide emissions. Sulfur dioxide causes acid rain but also creates sulfate aerosols in the atmosphere, which reflect sunlight and reduce global temperatures. After 1970, rising greenhouse gas levels and reduced sulfur pollution led to faster temperature increases.
Climate changes in recent times are unlike any seen for thousands of years. Many data sets show global surface temperatures rising by about 0.2°C each decade. The average temperature from 2014 to 2023 was 1.19°C higher than the pre-industrial baseline (1850–1900). Not every year is warmer than the previous one because natural climate patterns can cause yearly temperatures to vary by up to 0.2°C. Between 1998 and 2013, natural climate patterns like the Pacific Decadal Oscillation (PDO) and Atlantic Multidecadal Oscillation (AMO) caused a temporary slowdown in warming, called the "global warming hiatus." After this period, warming increased again, with 2024 being more than +1.5°C above the recent average. Scientists use 20-year averages to track long-term temperature trends and reduce the effects of short-term variations.
Other observations support the evidence of global warming. The upper atmosphere is cooling because greenhouse gases trap heat near Earth’s surface, reducing heat loss to space. Warming reduces snow cover and causes glaciers to retreat. At the same time, warmer temperatures increase ocean evaporation, leading to more atmospheric humidity and heavier rainfall. Plants are blooming earlier in spring, and many animal species are moving to cooler areas permanently.
Different parts of the world warm at different rates. Greenhouse gases spread globally because they stay in the atmosphere for a long time. Since the pre-industrial period, land areas have warmed almost twice as fast as the global average. This happens because oceans absorb more heat through evaporation and store large amounts of heat. Since at least 1970, the thermal energy in the climate system has increased, with over 90% of the extra heat stored in the ocean. The rest has heated the atmosphere, melted ice, and warmed the continents.
The Northern Hemisphere and the North Pole have warmed faster than the South Pole and Southern Hemisphere. The Northern Hemisphere has more land, snow, and sea ice, which reflect sunlight. When ice melts, these surfaces become darker and absorb more heat. Black carbon on snow and ice also contributes to Arctic warming. Arctic temperatures are rising three to four times faster than the rest of the world. Melting ice near the poles weakens ocean currents that move heat and precipitation around the globe.
The World Meteorological Organization estimates there is nearly a 50% chance that the average global temperature for five years will exceed +1.5°C between 2024 and 2028. The IPCC predicts the 20-year average temperature will exceed +1.5°C in the early 2030s.
The IPCC Sixth Assessment Report (2021) projected that by 2100, global warming is very likely to reach 1.0–1.8°C under low greenhouse gas emissions, 2.1–3.5°C under intermediate emissions, or 3.3–5.7°C under high emissions. Warming will continue past 2100 in intermediate and high emission scenarios, with temperature projections by 2300 similar to those from millions of years ago.
The remaining carbon budget to stay below certain temperature increases is calculated by modeling the carbon cycle and how sensitive the climate is to greenhouse gases. According to UNEP, there is a 50% chance of keeping global warming below 2.0°C if emissions after 2023 do not exceed 900 gigatonnes of CO₂. This budget equals about 16 years of current emissions.
Causes of recent global temperature rise
The climate system goes through natural cycles that can last for years, decades, or centuries. For example, El Niño events cause short-term increases in surface temperature, while La Niña events cause short-term cooling. How often these events happen can influence global temperature trends over decades. Other changes happen because of an imbalance in energy from outside factors. These include changes in greenhouse gas levels, solar energy output, volcanic eruptions, and shifts in Earth's orbit around the Sun.
To find out how much humans affect climate change, scientists compare unique "fingerprints" of all possible causes with what is actually observed and with natural climate changes. For example, changes caused by the Sun—where the whole atmosphere warms—can be ruled out because only the lower atmosphere has warmed. Tiny particles in the air, called aerosols, have a cooling effect. Other factors, like changes in how much sunlight is reflected by Earth’s surface, have smaller impacts.
Greenhouse gases let sunlight pass through the atmosphere to warm Earth’s surface. Earth then radiates this heat back into space. Greenhouse gases absorb some of this heat, slowing how quickly it escapes into space. This traps heat near Earth’s surface, making it warmer over time.
Water vapor (about 50%) and clouds (about 25%) are the largest contributors to the greenhouse effect. However, they change based on temperature and are mostly considered feedbacks that affect how sensitive the climate is to changes. In contrast, gases like carbon dioxide (about 20%), ozone, CFCs, and nitrous oxide are added or removed from the atmosphere independently of temperature. These are considered external factors that directly affect global temperatures.
Before the Industrial Revolution, natural levels of greenhouse gases made Earth’s surface about 33°C warmer than it would have been without them. Since then, human activities, especially burning fossil fuels (coal, oil, and natural gas), have increased greenhouse gas levels in the atmosphere. In 2022, carbon dioxide and methane levels were about 50% and 164% higher than in 1750. These CO2 levels are higher than they have been in the last 14 million years. Methane levels are much higher than they were in the last 800,000 years.
In 2019, human-caused greenhouse gas emissions were equal to 59 billion tonnes of CO2. Of this, 75% was CO2, 18% was methane, 4% was nitrous oxide, and 2% was fluorinated gases. Most CO2 comes from burning fossil fuels for energy in transport, manufacturing, heating, and electricity. Additional CO2 comes from deforestation and industrial processes, such as making cement, steel, aluminum, and fertilizer. Methane comes from livestock, manure, rice farming, landfills, wastewater, coal mining, and oil and gas extraction. Nitrous oxide mainly comes from the breakdown of fertilizer by microbes.
Methane stays in the atmosphere for about 12 years, but CO2 remains much longer. The Earth’s surface absorbs CO2 as part of the carbon cycle. Each year, plants on land and in the ocean absorb most of the extra CO2 released. However, this CO2 returns to the atmosphere when plants or other organic matter decays, burns, or is digested. Land-based processes, such as soil carbon storage and photosynthesis, remove about 29% of annual global CO2 emissions. The ocean has absorbed 20 to 30% of emitted CO2 over the last two decades. CO2 is only removed from the atmosphere for the long term when it is stored in Earth’s crust, a process that can take millions of years.
About 30% of Earth’s land is not usable for humans (glaciers, deserts, etc.), 26% is forests, 10% is shrubland, and 34% is agricultural land. Deforestation is a major cause of global warming because trees that are cut down release CO2, and new trees are not planted to replace them, removing a carbon sink. Between 2001 and 2018, 27% of deforestation was due to clearing land for agriculture, 24% was from temporary clearing for farming, 26% was from logging, and 23% was from wildfires. Some forests were not fully cleared but were damaged. Restoring these forests can help them absorb more CO2 again.
The type of plants on Earth’s surface affects how much sunlight is reflected back into space (albedo) and how much heat is lost through evaporation. For example, replacing a dark forest with grassland makes the surface lighter, reflecting more sunlight. Deforestation can also change the release of chemicals that affect clouds and wind patterns. In tropical and temperate regions, these changes lead to more warming, but in polar regions, replacing forests with snow-covered plains can cause cooling. Overall, changes in surface albedo from land use have had a slight cooling effect on global temperatures.
Air pollution, in the form of tiny particles called aerosols, affects the climate. Aerosols scatter and absorb sunlight. From 1961 to 1990, less sunlight reached Earth’s surface, a phenomenon called global dimming. This was mainly caused by sulfate aerosols from burning fuels like coal. Smaller contributions came from black carbon (from burning fuels and biomass) and dust. Since 1990, aerosols have decreased due to pollution controls, reducing their ability to mask the warming caused by greenhouse gases.
Aerosols also affect Earth’s energy balance indirectly. Sulfate aerosols act as cloud seeds, creating clouds with more and smaller droplets. These clouds reflect more sunlight than clouds with fewer, larger droplets. They also slow raindrop growth, making clouds more reflective. These indirect effects are the biggest uncertainty in how much aerosols influence climate.
While aerosols often reduce global warming by reflecting sunlight, black carbon in soot that lands on snow or ice can increase warming. This makes snow and ice absorb more heat, speeding up melting and raising sea levels. Reducing black carbon in the Arctic could lower global warming by 0.2°C by 2050. Reducing sulfur in ship fuel since 2020 is expected to increase global temperatures by 0.05°C by 2050.
The Sun is Earth’s main energy source, so changes in sunlight directly affect the climate. Solar energy has been measured by satellites and indirectly from the 1600s. Since 1880, there has been no increase in the Sun’s energy reaching Earth, even though the lower atmosphere has warmed. The upper atmosphere would warm if the
Modelling
A climate model is a tool that shows how the Earth's climate works by including things like natural changes, such as shifts in the Earth's orbit, changes in the Sun's energy over time, and effects from volcanic eruptions. These models help scientists predict how much the Earth's temperature might rise based on future emissions, considering how different climate effects can make changes stronger or weaker. They also help predict ocean currents, the pattern of seasons, and how carbon moves between the land and the air.
To test how accurate these models are, scientists compare their predictions to real climate conditions from the past or present. Some older models did not correctly predict how fast the Arctic ice was shrinking or how much rainfall was increasing. Models from earlier years also did not fully match the rise in sea levels since 1990, but newer models agree better with actual observations. A 2017 report from the United States said that climate models might still not fully account for some important effects that influence the climate. These models may also struggle to predict short-term changes in weather patterns in specific regions.
Some climate models include how people and societies affect the climate. These models study how population growth, economic development, and energy use influence the physical climate. Using this information, they create different scenarios for how much greenhouse gases might be released into the air in the future. These scenarios are then used by other models to predict how the amounts of greenhouse gases in the atmosphere might change. Based on different situations about society and efforts to reduce emissions, these models show a wide range of possible carbon dioxide levels in the air, from 380 to 1400 parts per million.
Impacts
The environmental effects of climate change are wide-ranging and affect oceans, ice, and weather. These changes can happen slowly or quickly. Evidence of these effects comes from studying past climate changes, using models, and observing the present. Since the 1950s, droughts and heat waves have occurred more often together. In India and East Asia, very wet or very dry events during the monsoon season have increased. Monsoonal rain in the Northern Hemisphere has grown more since 1980. The speed and strength of hurricanes and typhoons are likely increasing, and their areas may be expanding toward the poles because of warming. However, the number of tropical cyclones has not increased due to climate change.
Global sea levels are rising because of warmer water expanding and glaciers and ice sheets melting. Sea level rise has increased over time, reaching 4.8 centimeters each decade between 2014 and 2023. Over the 21st century, the IPCC predicts 32–62 centimeters of sea level rise under a low emission scenario, 44–76 centimeters under an intermediate one, and 65–101 centimeters under a high emission scenario. Processes in Antarctica, such as ice sheet instability, could add more sea level rise, possibly up to 2 meters by 2100 under high emissions.
Climate change has caused Arctic sea ice to shrink and thin over many years. At 1.5°C of warming, ice-free summers are rare, but at 2°C, they may happen every 3 to 10 years. Higher CO₂ levels in the atmosphere cause more CO₂ to dissolve in oceans, making them more acidic. Warmer water holds less oxygen, so ocean oxygen levels are dropping, and dead zones are growing.
Greater global warming increases the risk of crossing "tipping points"—points where major changes become unavoidable even if temperatures drop. For example, the Greenland ice sheet is already melting. If warming reaches 1.7°C to 2.3°C, it will continue melting until it disappears completely. Even if warming later decreases to 1.5°C or less, it will still lose much more ice than if it had never reached that threshold. While ice sheets may take thousands of years to melt, other tipping points, like the collapse of major ocean currents or damage to ecosystems like the Amazon rainforest and coral reefs, could happen faster. The collapse of ocean currents like the Atlantic meridional overturning circulation (AMOC) would cause severe cooling in the Northern Hemisphere.
Long-term effects of climate change on oceans include more ice melt, warmer oceans, rising sea levels, ocean acidification, and less oxygen in the water. These changes will take centuries to millennia because CO₂ stays in the atmosphere for a long time. After 2000 years, sea levels could rise about 2.3 meters per degree Celsius. Ocean acidification will continue for hundreds to thousands of years because CO₂ absorption is slow. Deep ocean areas (below 2,000 meters) are already losing over 10% of their oxygen due to past warming. The West Antarctic ice sheet is likely to melt irreversibly, raising sea levels by at least 3.3 meters over 2000 years.
Recent warming has caused many land and freshwater species to move toward the poles and higher elevations. For example, the range of hundreds of North American birds has shifted northward by 1.5 kilometers per year over the past 55 years. Higher CO₂ levels and longer growing seasons have increased plant growth globally. However, heatwaves and droughts have reduced productivity in some areas. The balance between these effects is unclear. Climate change has also caused woody plants to spread across 500 million hectares worldwide. Warmer temperatures have expanded dry regions, like deserts in the subtropics. Rapid global warming increases the chance of sudden ecosystem changes. Overall, climate change is expected to cause many species to go extinct.
Oceans have warmed more slowly than land, but ocean species have moved toward colder areas faster than land species. Ocean heatwaves, caused by climate change, harm corals, kelp, and seabirds. Ocean acidification makes it harder for marine organisms like mussels, barnacles, and corals to build shells and skeletons. Heatwaves have also caused coral bleaching. Climate change and pollution increase harmful algal blooms, which lower oxygen levels, disrupt food webs, and kill marine life. Coastal ecosystems are especially stressed, with nearly half of global wetlands lost due to climate change and other human activities. Plants are also suffering from increased insect damage.
Climate change affects people worldwide, with impacts visible on all continents and in all ocean regions. Areas near the equator and less developed regions face the greatest risks. Continued warming could have "severe, widespread, and irreversible" effects on people and ecosystems. These risks are uneven, but they are greater for disadvantaged people in both developed and developing countries.
The World Health Organization says climate change is one of the biggest threats to global health in the 21st century. Scientists warn that it causes irreversible harm. Extreme weather events harm public health, food, and water security. Extreme temperatures increase illness and death. Climate change makes extreme weather more intense and frequent. It also affects the spread of diseases like dengue fever and malaria. The World Economic Forum estimates 14.5 million more deaths could occur by 2050 due to climate change. About 30% of the global population lives in areas where extreme heat and humidity already cause extra deaths. By 2100, 50% to 75% of the global population may live in such areas.
While total crop yields have increased over the past 50 years due to better farming, climate change has slowed the rate of growth. Fisheries have declined in many regions. Some high-latitude areas have seen better agricultural productivity, but mid- and low-latitude areas have suffered. Climate change changes where crops can grow, often moving suitable areas to higher latitudes and altitudes. The World Economic Forum says increased drought could cause 3.2 million deaths from malnutrition by 2050 and harm children’s growth. At 2°C warming, global livestock numbers could drop by 7–10% by 2050 due to less animal feed. If emissions continue to rise, over 9 million climate-related deaths could happen each year by 2100.
Economic damage from climate change could be severe, with serious consequences in South-East Asia and sub-Saharan Africa, where
Reducing and recapturing emissions
Climate change can be lessened by reducing the amount of greenhouse gases released into the air and by increasing the amount of carbon dioxide removed from the air. To keep global warming below 2 °C, global greenhouse gas emissions must reach net-zero by 2070. This requires major, large-scale changes in energy, land use, cities, transportation, buildings, and industry.
The United Nations Environment Programme says countries need to increase their promises under the Paris Agreement three times within the next 10 years to limit warming to 2 °C. Based on current promises from the Paris Agreement as of 2024, there is a 66% chance global warming will stay below 2.8 °C by the end of the century (range: 1.9–3.7 °C, depending on how promises are carried out and technological progress). If only current policies are considered, warming could reach 3.1 °C. Globally, limiting warming to 2 °C may lead to more economic benefits than costs.
Most strategies to limit warming to 2 °C involve using more renewable energy and improving energy efficiency. To protect ecosystems and help them absorb more carbon, changes in agriculture and forestry are needed, such as stopping deforestation and restoring forests through reforestation.
Some methods to reduce climate change carry more risks. Strategies to limit warming to 1.5 °C often include using technologies to remove carbon dioxide from the air over the 21st century. However, these methods may have environmental risks.
Solar radiation modification (SRM) is a proposed way to cool the Earth by reflecting sunlight back into space. However, it does not reduce greenhouse gas levels and would not solve ocean acidification. It is not considered a true solution to climate change and should only be used as a backup, not a replacement, due to risks like sudden warming if stopped. The most studied SRM method is injecting particles into the atmosphere. While SRM might reduce some effects of warming, it could cause changes in rainfall and face political challenges.
Renewable energy is essential to reducing climate change. For many years, fossil fuels have provided about 80% of the world’s energy, with the rest coming from nuclear power and renewables like hydropower, wind, solar, and geothermal. Fossil fuel use is expected to peak before 2030 and then decline, especially for coal. In 2023, 86% of new electricity generation came from renewables. Other clean energy sources, like nuclear and hydropower, currently supply more energy but are expected to grow more slowly.
Solar panels and wind power are now among the cheapest ways to generate electricity in many areas. To shift quickly from fossil fuels to renewables, policies supporting green energy are needed. To reach carbon neutrality by 2050, renewables would need to provide most of the world’s electricity, possibly 85% or more. Investment in coal would stop, and coal use would nearly end by 2050.
Renewable energy must also become the main source of energy for heating and transportation. Transportation can move away from gasoline-powered vehicles to electric vehicles, public transit, and walking or cycling. For shipping and flying, low-carbon fuels can reduce emissions. Heating can use less carbon with technologies like heat pumps.
Challenges to growing clean energy include the fact that wind and solar energy are not always available and depend on weather. In the past, hydroelectric dams and fossil fuel plants have been used when renewable energy is low. In the future, battery storage, better matching of energy supply and demand, and long-distance power lines can help manage this. Bioenergy may not always be carbon-neutral and could affect food supplies. Nuclear energy faces challenges like radioactive waste and safety concerns. Hydropower growth is limited because the best sites for dams are already used, and new projects face social and environmental issues.
Using low-carbon energy improves human health by reducing air pollution, which causes about 7 million deaths each year. Meeting Paris Agreement goals to limit warming to 2 °C could save about 1 million lives annually by 2050. Limiting warming to 1.5 °C could save even more lives, improve energy security, and reduce poverty. Cleaner air also has economic benefits that may outweigh the costs of reducing emissions.
Reducing energy use is another key way to cut emissions. Using less energy makes it easier to develop clean energy and manage the electricity grid. Major investments in energy efficiency will be needed, similar to investments in renewable energy. Changes in energy use during the pandemic have made future energy forecasts harder to predict.
Ways to reduce energy use vary by industry. In transportation, people can use more efficient travel options like buses, trains, or electric vehicles. In industry, improving heating systems, using less energy in manufacturing, and making products last longer can help. In buildings, new designs and upgrades to older buildings can improve energy efficiency. Technologies like heat pumps can also help.
Agriculture and forestry must address three challenges: reducing emissions, stopping the loss of forests to farming, and meeting rising food demand. Actions like reducing food demand, increasing land productivity, protecting forests, and cutting emissions from farming could reduce agriculture and forestry emissions by two-thirds from 2010 levels.
Reducing meat and dairy production is a key step in cutting emissions. Livestock farming produces about three-quarters of all emissions from agriculture and land use. Livestock also uses 37% of land not covered by ice and consumes crops grown on 12% of land, contributing to deforestation and land damage.
Steel and cement production account for about 13% of industrial carbon emissions. These industries use materials that release carbon, so reducing emissions requires new chemical methods. When industries produce carbon waste, technology can sometimes capture and store it.
Adaptation
Adaptation is the process of adjusting to changes in climate and its effects. Without efforts to reduce climate change, adaptation alone cannot stop the risk of very serious, widespread, and permanent harm. More extreme climate changes require bigger changes in how people adapt, which can be very expensive. The ability and chance for people to adapt differ in different places and groups, and developing countries usually have less. From 2001 to 2020, most low- and middle-income countries improved their ability to adapt by gaining better access to clean water and electricity, but progress has been slow. Many countries have created policies to help with adaptation. However, there is a large gap between the money needed and the money available.
Adapting to rising sea levels includes avoiding areas at risk of flooding, learning to live with more frequent floods, and building barriers to stop floods. If these steps fail, moving people away from dangerous areas may be necessary. There are economic challenges in dealing with extreme heat. Avoiding heavy work or using air conditioning is not always possible for everyone. In farming, adapting can involve switching to more sustainable food choices, growing a variety of crops, controlling soil erosion, and improving crops to survive changing conditions. Insurance helps share risks, but it is often hard for people with low incomes to get. Education, moving to safer places, and early warning systems can help reduce the dangers of climate change. Planting mangroves or other plants along coasts can protect against strong storms.
Ecosystems also adapt to climate change, and humans can help this process. Connecting ecosystems allows animals and plants to move to better climates. Species can be moved to areas with more suitable conditions. Protecting and restoring natural areas helps ecosystems become stronger, making it easier for them to adapt. Many actions that help ecosystems adapt also help humans. For example, restoring natural fire patterns reduces the chance of large fires and protects people. Giving rivers more space allows more water to be stored naturally, reducing flood risks. Restored forests absorb carbon dioxide, but planting trees in areas that are not suitable can worsen climate problems.
Adapting to climate change can work well with reducing climate change, but there are also challenges. One benefit is increased food production, which helps both adaptation and reducing climate change. One challenge is that using more air conditioning helps people deal with heat, but it uses more energy. Another challenge is that building cities more densely can reduce emissions from transportation and construction, but it may also increase heat in cities, putting people at risk from heat-related health issues.
Policies and politics
Countries that are most affected by climate change usually produce a small amount of global emissions. This raises questions about fairness and justice. Limiting global warming helps achieve the United Nations' Sustainable Development Goals, such as ending poverty and reducing inequality. Goal 13 of these goals states the need to "take urgent action to combat climate change and its impacts." Goals related to food, clean water, and protecting ecosystems work together with efforts to reduce climate change.
The global politics of climate change are complex. It is often described as a situation where some countries benefit from the actions of others without making changes themselves. However, reducing emissions can also have local benefits. For example, stopping the use of coal improves public health and the environment in most areas. Countries that rely on imported fossil fuels can save money by switching to clean energy, while countries that export fossil fuels may lose value in their resources.
Many policies, rules, and laws are being used to reduce emissions. As of 2019, carbon pricing covered about 20% of global greenhouse gas emissions. Carbon can be priced through taxes or systems that allow trading of emissions. In 2017, direct global subsidies for fossil fuels reached $319 billion, and $5.2 trillion when indirect costs like air pollution are included. Ending these subsidies could reduce global carbon emissions by 28% and air pollution deaths by 46%. Money saved from subsidies could support the shift to clean energy. Other methods to reduce emissions include setting standards for vehicle efficiency, renewable fuel use, and air pollution rules for heavy industries. Some countries require energy companies to increase the use of renewable energy. An international group was formed in 2025 to create a global system for trading emissions, which could increase emissions reductions seven times more than current efforts, provide $200 billion yearly for clean energy and social programs, and help meet the goals of the Paris Agreement.
Policies focused on climate justice aim to address human rights and inequality. Supporters of climate justice believe that those most responsible for climate change should pay for adaptation efforts, while those affected by climate change should receive support. One way to do this is for wealthy nations to provide funding to poorer countries for climate adaptation.
Oxfam reported that in 2023, the wealthiest 10% of people were responsible for 50% of global emissions, while the poorest 50% were responsible for only 8%. Looking at emissions by production, the top 21 fossil fuel companies would owe $5.4 trillion in climate reparations from 2025 to 2050. To ensure a fair transition, workers in the fossil fuel industry would need new jobs, and their communities would need investments.
Nearly all countries are part of the 1994 United Nations Framework Convention on Climate Change (UNFCCC). The goal of the UNFCCC is to prevent dangerous human harm to the climate system. This includes stabilizing greenhouse gas levels so ecosystems can adapt, food production is not threatened, and economic growth can continue. The UNFCCC itself does not set emission limits but provides a framework for agreements that do. Global emissions have increased since the UNFCCC was created. Its yearly meetings are where global climate negotiations take place.
The 1997 Kyoto Protocol expanded the UNFCCC and required most developed countries to legally limit their emissions. During negotiations, developing countries pushed for developed nations to "take the lead" in reducing emissions, as developed countries contributed more to climate change. At the time, developing countries had lower emissions per person and needed to emit more to meet their development goals.
The 2009 Copenhagen Accord was criticized for setting low goals and was rejected by poorer nations, including the G77. The agreement aimed to limit global temperature rise to below 2°C and promised $100 billion yearly for developing countries by 2020. A fund called the Green Climate Fund was also created. By 2020, only $83.3 billion was delivered, and the target was expected to be met in 2023.
In 2015, all UN countries agreed to the Paris Agreement, which aims to keep global warming well below 2.0°C and includes a goal of keeping warming below 1.5°C. The Paris Agreement replaced the Kyoto Protocol. Unlike Kyoto, it does not set legally binding emission targets. Instead, it requires countries to regularly set more ambitious goals and review them every five years. The agreement reaffirmed that developing countries need financial support. As of March 2025, 194 countries and the European Union have joined the agreement.
The 1987 Montreal Protocol, an agreement to stop using ozone-depleting gases, has helped reduce climate change. Some of these gases are strong greenhouse gases, and banning them may have prevented a temperature rise of 0.5°C–1.0°C. The agreement has been more effective at reducing greenhouse gas emissions than the Kyoto Protocol. The 2016 Kigali Amendment to the Montreal Protocol aims to reduce emissions of hydrofluorocarbons, which are powerful greenhouse gases. If countries follow the amendment, it could prevent a warming of 0.3°C–0.5°C.
In 2019, the United Kingdom became the first national government to declare a climate emergency. Other countries followed. The same year, the European Parliament declared a "climate and environmental emergency." The European Commission introduced the European Green Deal, aiming to make the EU carbon-neutral by 2050. In 2021, the European Commission released "Fit for 55," a plan requiring all new cars in Europe to be zero-emission vehicles by 2035.
Major Asian countries have made similar commitments: South Korea and Japan aim to be carbon-neutral by 2050, and China by 2060. India supports renewable energy but plans to expand coal use. Vietnam, a country that relies heavily on coal, pledged to phase out coal power by the 2040s or as soon as possible.
As of 2021, based on 48 national climate plans covering 40% of Paris Agreement participants, estimated total greenhouse gas emissions would be 0.5% lower than 2010 levels. This is below the 45% or 25% reduction goals needed to limit global warming to 1.5°C or 2°C, respectively.
Society and culture
Public debate about climate change has been influenced by climate change denial and misinformation. These ideas first appeared in the United States and later spread to other countries, such as Canada and Australia. They originated from fossil fuel companies, industry groups, conservative think tanks, and some scientists. Similar to the tobacco industry, these groups often create doubt about scientific findings related to climate change. People who question the science of climate change are sometimes called "skeptics," but "contrarians" or "deniers" are more accurate terms.
There are different types of climate denial. Some people deny that the Earth is warming at all. Others accept that warming is happening but believe it is caused by natural factors. Some downplay the harmful effects of climate change. Over time, creating doubt about the science led to a false controversy, making people think there is disagreement among scientists about climate change. This was done to delay action on the issue. Tactics used include criticizing scientific institutions and questioning scientists' motives. Climate-denying blogs and media have also helped spread misunderstandings.
Climate change became widely known internationally in the late 1980s. In the 1990s, media coverage sometimes confused climate change with other environmental issues, such as ozone depletion. In popular culture, the movie The Day After Tomorrow (2004) and the documentary An Inconvenient Truth (2006) brought attention to climate change.
Public concern and understanding of climate change vary by region, gender, age, and political views. More educated people, as well as women and younger individuals in some countries, are more likely to see climate change as a serious threat. College biology textbooks from the 2010s included less information about climate change than those from earlier years, with fewer details on solutions. In many countries, differences in political beliefs also affect how people view climate change. Countries that produce a lot of carbon dioxide emissions often show less concern. Media coverage of protests has influenced public focus on specific aspects of climate change. People who are more worried about climate change tend to support policies that address it. Concern has grown over time, and in 2021, most people in 30 countries felt strongly worried about climate change or saw it as a global emergency. A 2024 survey across 125 countries found that 89% of people wanted stronger political action on climate change, but they often underestimated how much others were willing to act.
Climate protests push political leaders to take action against climate change. These protests can include public demonstrations, efforts to stop investing in fossil fuels, lawsuits, and other activities. One well-known protest is the School Strike for Climate, where young people around the world have skipped school on Fridays since 2018. This movement was started by a Swedish teenager named Greta Thunberg. Groups like Extinction Rebellion have also organized large protests, such as blocking roads and public transportation.
Lawsuits are increasingly used to encourage climate action by governments and companies. Activists often file lawsuits against governments, demanding they take strong action or follow existing climate laws. Lawsuits against fossil fuel companies usually seek money for harm caused by climate change. On July 23, 2025, the UN's International Court of Justice stated that countries must take steps to stop climate change. If countries fail to do this, other countries can sue them. This includes following agreements they have signed, such as the 2015 Paris Climate Accord.
History
In the 19th century, scientists like Alexander von Humboldt began to predict the effects of climate change. In the 1820s, Joseph Fourier proposed the greenhouse effect to explain why Earth's temperature was higher than the Sun's energy alone could explain. Earth's atmosphere allows sunlight to pass through, so sunlight reaches the surface and becomes heat. However, the atmosphere does not allow heat from the surface to escape easily, trapping some heat and warming the planet. In 1856, Eunice Newton Foote showed that air with water vapor warms more than dry air, and that air with carbon dioxide (CO₂) warms even more. In her work, she wrote that "[a]n atmosphere of that gas would give to our earth a high temperature."
Starting in 1859, John Tyndall discovered that nitrogen and oxygen, which make up 99% of dry air, allow heat to pass through. However, water vapor and gases like methane and carbon dioxide absorb heat and release it back into the atmosphere. Tyndall suggested that changes in the amounts of these gases might have caused past climate changes, such as ice ages.
Svante Arrhenius noted that water vapor levels in the air change often, but CO₂ levels are influenced by long-term geological processes. He explained that increased CO₂ levels could cause warming, which would increase water vapor, creating a cycle that amplifies warming. In 1896, he created the first climate model of its kind, predicting that halving CO₂ levels could lead to a temperature drop and an ice age. Arrhenius estimated that doubling CO₂ levels could raise Earth's temperature by about 5–6 °C. Some scientists were skeptical, believing the greenhouse effect was already complete and that the climate would balance itself. Beginning in 1938, Guy Stewart Callendar presented evidence that Earth was warming and CO₂ levels were rising, but his findings faced similar doubts.
In the 1950s, Gilbert Plass developed a detailed computer model that included different layers of the atmosphere and the infrared spectrum. This model predicted that rising CO₂ levels would cause warming. Around the same time, Hans Suess found evidence that CO₂ levels were increasing, and Roger Revelle showed that the oceans would not absorb all the extra CO₂. These scientists helped Charles Keeling start a long-term record of CO₂ levels, known as the "Keeling Curve," which became part of ongoing research into whether humans caused global warming. Studies like the National Research Council's 1979 Charney Report supported the accuracy of climate models that predicted significant warming. In 1988, James Hansen presented evidence in a US Senate hearing that human activities caused observed global warming and warned of the dangers of uncontrolled warming. The Intergovernmental Panel on Climate Change (IPCC), created in 1988, provided formal advice to governments and encouraged research across scientific fields. IPCC reports include summaries of scientific discussions published in peer-reviewed journals.
Almost all scientists agree that Earth's climate is warming and that this is caused by human activities. No major scientific organization disagrees with this view. By 2019, over 99% of recent scientific studies supported this conclusion. The 2021 IPCC Assessment Report stated that human-caused climate change is "unequivocal." Scientists now agree that action is needed to protect people from climate change's impacts. National science academies have urged world leaders to reduce global emissions.
Extreme event attribution (EEA), also called attribution science, was developed in the early 2000s. EEA uses climate models to determine how human-caused climate change affects the frequency, strength, length, and effects of specific extreme weather events. Studies using EEA allow scientists to say, for example, "this weather event was made at least n times more likely by human-caused climate change" or "this heatwave was m degrees hotter than it would have been without global warming" or "this event was nearly impossible without climate change."
Better computers in the 2000s and new scientific ideas in the 2010s allowed scientists to study climate change's effects on weather events with high confidence. Scientists use methods and models that have already been reviewed by other scientists, enabling "rapid attribution studies" to be published quickly after weather events occur.