Climate change today includes global warming, which is the steady rise in Earth's average temperature, and the larger effects this warming has on Earth's climate. Climate change also refers to long-term changes in Earth's climate that happened in the past. The recent increase in Earth's temperature 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 had at the end of the pre-industrial era. These levels are the highest in millions of years.
Climate change is having a bigger effect 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 other extreme weather events. Rapid changes in mountains, coral reefs, and the Arctic are pushing many animal and plant 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 affects people by increasing floods, extreme heat, shortages of food and water, more diseases, and economic losses. It can also cause people to move and lead to conflicts. The World Health Organization says climate change is one of the greatest threats to health in the 21st century. Without action to limit warming, societies and ecosystems will face more severe 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 little of the world's emissions but have the least ability to adapt and are most at risk from climate change.
Many climate change effects have been observed in the early 21st century. The year 2024 was the warmest on record, with temperatures 1.60°C (2.88°F) higher than in 1850, when tracking began. More warming will increase these effects and could trigger major changes, 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, even with current plans, global warming is expected to reach about 2.8°C (5.0°F) by the end of the century.
There is strong global support for action to address climate change, and most countries aim to stop releasing carbon dioxide. Fossil fuels can be reduced by ending their subsidies, saving energy, and using energy sources that do not create much pollution. These sources include wind, solar, hydro, and nuclear power. Clean electricity can replace fossil fuels for transportation, heating homes, and industrial processes. Carbon can also be removed from the air by planting more forests and using farming methods that store carbon in soil.
Terminology
Before the 1980s, scientists were unsure if the warming caused by greenhouse gases was stronger than the cooling caused by pollution particles in the air. At that time, they called human effects on the climate "inadvertent climate modification." In the 1980s, the terms "global warming" and "climate change" became more commonly used and were often treated as the same. Scientifically, "global warming" only refers to the rise in Earth's average surface temperature, while "climate change" includes 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.
"Global warming," first used in 1975, became more popular after a scientist named James Hansen used it in a speech in the U.S. Senate in 1988. Since the 2000s, the term "climate change" has been used more often. Some scientists, politicians, and media now use terms like "climate crisis," "climate emergency," or "global heating" to describe climate change.
Global temperature rise
Over millions of years, Earth's climate has changed between cold 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 to 1.5 degrees Celsius warmer than before global warming began. Sea levels were 5 to 10 meters higher than today. The most recent ice age, 20,000 years ago, was 5 to 7 degrees Celsius colder. Sea levels were over 125 meters lower than today during this time.
Temperatures became more stable about 11,700 years ago, marking the start of the current warm period. This time also saw the beginning of agriculture. In the past, warming and cooling periods, such as the Medieval Warm Period and the Little Ice Age, did not happen at the same time in all regions. Some areas may have had temperatures as high as those in the late 20th century. Scientists use natural records like tree rings and ice cores to study climate from that time.
Starting around 1850, thermometers began to measure global temperatures. From the 18th century to 1970, there was little overall warming because the cooling effect of sulfur dioxide emissions balanced the warming caused by greenhouse gases. Sulfur dioxide causes acid rain and creates sulfate particles in the air that reflect sunlight, reducing global temperatures. After 1970, rising greenhouse gas levels and reduced sulfur pollution caused temperatures to rise more quickly.
Climate changes today are unlike those seen for thousands of years. Many sources show global surface temperatures increasing by about 0.2 degrees Celsius every decade. From 2014 to 2023, the average temperature was 1.19 degrees Celsius higher than the pre-industrial average (1850–1900). Not every year is warmer than the previous one because natural climate patterns can cause yearly temperature changes of up to 0.2 degrees Celsius. Between 1998 and 2013, two climate patterns, the Pacific Decadal Oscillation and Atlantic Multidecadal Oscillation, slowed warming temporarily. This period was called the "global warming hiatus." After this time, temperatures rose rapidly, with 2024 being more than 1.5 degrees Celsius above the recent average. Scientists use 20-year averages to track long-term warming trends and reduce the influence of short-term changes.
Other observations support the evidence of global warming. The upper atmosphere is cooling because greenhouse gases trap heat near Earth's surface, reducing the amount of heat that escapes into space. Warming reduces snow cover and causes glaciers to shrink. At the same time, more heat from oceans increases atmospheric humidity, leading to more and heavier rain. Plants are blooming earlier in spring, and many animal species are moving to cooler areas.
Different parts of the world warm at different rates. Greenhouse gases spread globally because they remain in the atmosphere for a long time. Since the pre-industrial era, land areas have warmed nearly twice as fast as the global average. Oceans absorb more heat through evaporation and store large amounts of energy. Since 1970, over 90% of the extra energy from warming has been stored in the ocean, while the rest has heated the atmosphere, melted ice, and warmed land.
The Northern Hemisphere and the North Pole are warming 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 around the globe, changing weather patterns worldwide.
The World Meteorological Organization estimates there is nearly a 50% chance that the average global temperature will exceed +1.5 degrees Celsius between 2024 and 2028. Scientists predict that the 20-year average temperature will surpass +1.5 degrees Celsius in the early 2030s.
According to the IPCC Sixth Assessment Report (2021), global warming is likely to reach 1.0–1.8 degrees Celsius by 2100 if emissions are very low, 2.1–3.5 degrees Celsius under an intermediate emissions scenario, or 3.3–5.7 degrees Celsius under a high emissions scenario. Warming will continue past 2100 in the intermediate and high emission scenarios, with projected temperatures by 2300 similar to those from millions of years ago.
The amount of carbon that can be released while keeping warming below certain levels depends on how much heat the climate system can absorb. Scientists estimate that to have a 50% chance of keeping warming below 2.0 degrees Celsius, global emissions after 2023 must not exceed 900 gigatonnes of CO₂. This amount of carbon would be used up in about 16 years at current emission rates.
Causes of recent global temperature rise
The climate system goes through natural cycles that can last for years, decades, or even 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 forces. These include changes in greenhouse gas levels, changes in the Sun's brightness, volcanic eruptions, and changes in Earth's orbit around the Sun.
To understand how much humans affect climate change, scientists look for unique "fingerprints" of all possible causes and compare them to what is actually observed and to natural climate changes. For example, solar changes—where the entire atmosphere warms—can be ruled out because only the lower atmosphere has warmed. Aerosols in the air cause a small cooling effect. Other factors, like changes in how much sunlight is reflected by Earth's surface, have less impact.
Greenhouse gases let sunlight pass through the atmosphere to warm Earth's surface. Earth then sends this heat back into space as infrared radiation. 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 biggest contributors to the greenhouse effect. However, they change based on temperature and are mostly seen as feedbacks that affect how sensitive the climate is to changes. Other gases, like carbon dioxide (about 20%), tropospheric ozone, CFCs, and nitrous oxide, change independently of temperature and are considered external factors that influence 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 the Industrial Revolution, human activities like burning fossil fuels (coal, oil, and natural gas) have increased greenhouse gas levels. In 2022, carbon dioxide and methane levels were about 50% and 164% higher than they were in 1750. These carbon dioxide 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 carbon dioxide. Of this, 75% was carbon dioxide, 18% was methane, 4% was nitrous oxide, and 2% was fluorinated gases. Most carbon dioxide emissions come from burning fossil fuels for energy, transportation, manufacturing, heating, and electricity. Additional emissions come from deforestation and industrial processes, such as cement, steel, aluminum, and fertilizer production. Methane emissions come from livestock, manure, rice farming, landfills, wastewater, coal mining, and oil and gas extraction. Nitrous oxide emissions mostly come from the breakdown of fertilizer by microbes.
Methane stays in the atmosphere for about 12 years, but carbon dioxide remains much longer. The Earth's surface absorbs carbon dioxide as part of the carbon cycle. Plants on land and in the ocean absorb most extra carbon dioxide each year, but this carbon dioxide returns to the atmosphere when plants or other organic matter decay, burn, or are digested. Land-based processes, like soil carbon storage and photosynthesis, remove about 29% of annual global carbon dioxide emissions. The ocean has absorbed 20 to 30% of emitted carbon dioxide over the last two decades. Carbon dioxide is only removed from the atmosphere for a long time 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 by humans (glaciers, deserts, etc.), 26% is forests, 10% is shrubland, and 34% is agricultural land. Deforestation is the main cause of land use changes that contribute to global warming. Destroyed trees release carbon dioxide, and new trees are not planted to replace them, reducing the ability of forests to act as carbon sinks. Between 2001 and 2018, 27% of deforestation was for permanent agricultural expansion, 24% was from temporary clearing for shifting cultivation, 26% was from logging, and 23% was from wildfires. Some forests are not fully cleared but are degraded. Restoring these forests helps them become carbon sinks again.
The type of vegetation 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 chemical compounds that affect clouds and wind patterns. In tropical and temperate areas, these changes lead to warming, but restoring forests can cool local temperatures. Near the poles, replacing forests with snow-covered plains (which reflect more sunlight) can cause cooling. Overall, changes in surface albedo from land use changes have been the main direct effect on temperature. So far, land use changes are estimated to have a slight cooling effect.
Air pollution, in the form of tiny particles called aerosols, affects the climate. These particles scatter and absorb sunlight. Between 1961 and 1990, less sunlight reached Earth's surface, a phenomenon called global dimming. This was mainly caused by sulfate aerosols from burning fossil fuels like coal and bunker fuel. Smaller contributions came from black carbon (from burning fossil fuels and biomass) and dust. Since 1990, aerosol levels have decreased due to pollution controls, reducing their ability to mask the warming caused by greenhouse gases.
Aerosols also indirectly affect Earth's energy balance. Sulfate aerosols act as cloud condensation nuclei, leading to clouds with more and smaller droplets. These clouds reflect more sunlight than clouds with fewer and larger droplets. They also reduce raindrop growth, making clouds more reflective. These indirect effects are the largest uncertainty in how much energy is added or removed from Earth's system.
While aerosols usually 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 sunlight, speeding up melting and raising sea levels. Reducing new black carbon deposits in the Arctic could lower global warming by 0.2°C by 2050. The reduction in sulfur content of fuel oil for ships 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 amount of solar energy reaching Earth, even though the lower atmosphere (
Modelling
A climate model is a way of showing the physical, chemical, and biological processes that influence the climate system. These models include natural processes, such as changes in Earth's orbit, historical changes in the Sun's activity, and effects from volcanic eruptions. They are used to estimate how much warming future emissions might cause by considering how climate feedbacks, such as changes in ice cover or plant growth, affect the system. Models also predict ocean currents, the yearly cycle of seasons, and the movement of carbon between Earth's surface and the atmosphere.
The accuracy of models is tested by checking how well they can recreate today's or past climates. Earlier models did not predict how fast the Arctic was shrinking or how quickly precipitation was increasing. Models from before the 1990s underestimated how much sea levels had risen since that time, but newer models match observations closely. The 2017 United States National Climate Assessment states that "climate models may still be underestimating or missing relevant feedback processes." Additionally, models may not always predict short-term changes in climate in specific regions.
Some climate models include factors related to society, such as population growth, economic development, and energy use. These models show how these factors influence and interact with the physical climate. Using this information, they create scenarios for future greenhouse gas emissions. These scenarios are then used as input for physical climate models and carbon cycle models to predict how greenhouse gas concentrations in the atmosphere might change. Depending on the chosen scenarios for society and efforts to reduce emissions, models predict atmospheric carbon dioxide levels that range from 380 to 1400 parts per million (ppm).
Impacts
Climate change affects many parts of the environment, such as oceans, ice, and weather. These changes can happen slowly or quickly. Scientists learn about these effects by studying past climate changes, using models, and observing the world today. Since the 1950s, droughts and heat waves have happened more often together. In India and East Asia, wet or dry events during the monsoon season have become more frequent. Rainfall during monsoons in the Northern Hemisphere has increased since 1980. Hurricanes and typhoons may be getting stronger and moving closer to the poles because of warming. However, the number of tropical cyclones has not increased because of climate change.
Global sea levels are rising because water expands as it warms and because glaciers and ice sheets are melting. Sea level rise has sped up, increasing by 4.8 centimeters every 10 years between 2014 and 2023. The IPCC predicts that by the end of the 21st century, sea levels could rise 32–62 centimeters under a low emission scenario, 44–76 centimeters under an intermediate one, and 65–101 centimeters under a very high emission scenario. Ice melting in Antarctica could add more than 2 meters to sea levels by 2100 under high emissions.
Climate change has caused Arctic sea ice to shrink and thin over many years. Ice-free summers are rare if warming stays below 1.5°C, but they could happen every 3 to 10 years if warming reaches 2°C. Higher carbon dioxide levels in the atmosphere mean more CO₂ dissolves in the ocean, making it more acidic. Warmer water holds less oxygen, so ocean oxygen levels are dropping, and "dead zones" are growing.
Greater 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, but if warming reaches 1.7°C to 2.3°C, it will continue melting until it disappears completely. Even if warming is later reduced to 1.5°C or less, the ice sheet will still lose much more ice than if warming had never reached that level. While ice sheets may take thousands of years to melt, other tipping points, like the collapse of ocean currents or damage to ecosystems like the Amazon rainforest and coral reefs, could happen in decades. 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 melting, warmer water, rising sea levels, ocean acidification, and less oxygen. These changes will take centuries or millennia because CO₂ stays in the atmosphere for a long time. Scientists estimate that sea levels could rise 2.3 meters for every degree Celsius of warming after 2000 years. Ocean acidification will continue for hundreds to thousands of years because the ocean absorbs CO₂ slowly. Deep ocean areas (below 2,000 meters) have already lost over 10% of their oxygen due to past warming. The West Antarctic ice sheet is likely to melt completely over 2000 years, raising sea levels by at least 3.3 meters.
Recent warming has caused many land and freshwater species to move toward the poles and higher altitudes. For example, the ranges of hundreds of North American birds have shifted northward by 1.5 kilometers per year over the past 55 years. Higher CO₂ levels and longer growing seasons have increased global plant growth. However, heat waves and droughts have reduced productivity in some regions. The future balance of these effects is unclear. Climate change has also caused woody plants to spread across 500 million hectares globally. Drier conditions, like expanding deserts in the subtropics, are linked to climate change. The speed and scale of warming may cause sudden changes in ecosystems, leading to the extinction of many species.
Oceans have warmed more slowly than land, but ocean species have moved toward colder areas faster than land species. Heat waves in the ocean, 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. Heat waves have also caused coral bleaching. Harmful algae blooms, worsened by climate change and pollution, lower oxygen levels, disrupt food webs, and kill marine life. Coastal ecosystems are especially stressed. Nearly half of global wetlands have been lost due to climate change and human activities. Plants are also suffering from insect damage.
Climate change affects people everywhere, with the greatest risks in less developed, low-latitude regions. Continued warming could cause "severe, pervasive, and irreversible" impacts on people and ecosystems. Risks are uneven, but disadvantaged groups in both developing and developed countries face greater dangers.
The World Health Organization says climate change is one of the biggest threats to global health in the 21st century. Scientists warn about its irreversible harms. 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 people could live in such areas.
Although 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. While some high-latitude areas have seen improved agricultural productivity, mid- and low-latitude areas have suffered. Climate change changes where crops can grow, shifting suitable areas to higher latitudes and altitudes. The World Economic Forum predicts that increased drought could cause 3.2 million deaths from malnutrition by 2050 and stunting in children. With 2°C of 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 occur each year by 2100.
Economic damage from climate change could be severe, with disastrous consequences likely in Southeast Asia and sub-Saharan Africa, where many people rely on natural and agricultural resources. Heat stress can stop outdoor workers from doing their jobs. If warming reaches 4°C, labor capacity in these regions could drop significantly.
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, worldwide greenhouse gas emissions must reach net-zero by 2070. This requires major, widespread changes in energy, land use, cities, transportation, buildings, and industry.
The United Nations Environment Programme says countries must increase their promises under the Paris Agreement three times in the next ten years to keep global warming below 2 °C. If current promises under the Paris Agreement are followed, there is a 66% chance that 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 how technology advances). If only current policies are considered, warming could reach 3.1 °C. Globally, keeping warming below 2 °C may lead to more economic benefits than costs.
Most plans to limit warming to 2 °C involve using more renewable energy and improving energy efficiency to reduce greenhouse gas emissions. Changes in agriculture and forestry, such as stopping deforestation and restoring natural ecosystems through reforestation, can also help reduce pressure on ecosystems and improve their ability to store carbon.
Some methods to reduce climate change carry greater risks. Plans to limit warming to 1.5 °C often include using large amounts of technology to remove carbon dioxide from the air over the 21st century. However, there are concerns about relying too much on these technologies and their environmental effects.
Solar radiation modification (SRM) is an idea to reduce warming by reflecting sunlight back into space. It does not reduce greenhouse gas levels, so it would not help with ocean acidification. SRM should not replace efforts to reduce emissions but could be used as a backup. The most studied SRM method is injecting particles into the atmosphere. While SRM might reduce warming and some of its effects, it could also cause problems like changes in rainfall patterns and political disagreements about its use.
Renewable energy is important for reducing climate change. For many years, fossil fuels have provided about 80% of the world’s energy. The rest comes from nuclear power and renewables, such as hydropower, wind, solar, and geothermal energy. Fossil fuel use is expected to reach its highest point before 2030 and then decrease, especially for coal. In 2023, 86% of new electricity generation came from renewable sources. Other clean energy sources, like nuclear and hydropower, currently supply more energy but may not grow as quickly in the future.
Solar panels and wind power are now among the cheapest ways to generate electricity in many areas. Policies that support green energy are needed to move quickly from fossil fuels to renewables. To reach carbon neutrality by 2050, renewable energy must become the main source of electricity, reaching 85% or more in some plans. Investment in coal will stop, and coal use will nearly end by 2050.
Renewable energy must also become the main source of energy for heating and transportation. Transportation can shift 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 cleaner technologies like heat pumps.
Challenges to growing clean energy include the fact that wind and solar power produce energy only sometimes and vary with the seasons. 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 use and supply, and long-distance power lines can help manage renewable energy. Bioenergy may not be carbon-neutral and could harm food supplies. Nuclear power faces challenges like radioactive waste and safety concerns. Hydropower growth is limited because the best locations for dams are already used, and new projects face social and environmental issues.
Using low-carbon energy improves health by reducing climate change and air pollution, which caused about 7 million deaths each year in 2016. Meeting Paris Agreement goals to limit warming to 2 °C could save about 1 million lives yearly by 2050. Limiting warming to 1.5 °C could save millions of lives, improve energy security, and reduce poverty. Better air quality also has economic benefits that may outweigh the costs of reducing emissions.
Reducing energy use is another way to cut emissions. Using less energy makes it easier to develop clean energy and manage the electricity grid, reducing the need for carbon-heavy infrastructure. Large investments in energy efficiency will be needed to meet climate goals, similar to investments in renewable energy. Changes in energy use during the pandemic have made future energy forecasts more uncertain.
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, designing products that use less energy, and making products last longer can help. In buildings, new designs and energy-efficient upgrades can reduce energy use. Technologies like heat pumps can also improve efficiency.
Agriculture and forestry must address three challenges: reducing greenhouse gas emissions, stopping the loss of forests to farmland, and meeting growing food demand. Actions like reducing food demand, improving land productivity, protecting forests, and reducing emissions from farming could cut agriculture and forestry emissions by two-thirds from 2010 levels.
Reducing meat and dairy production is key to cutting emissions. Removing livestock for meat and dairy could cut about three-quarters of emissions from agriculture. Livestock also use 37% of land and consume feed from 12% of farmland, contributing to deforestation and land damage.
Steel and cement production account for about 13% of industrial CO₂ emissions. These industries rely on carbon-heavy materials like coke and lime, so reducing emissions requires new chemical methods. When energy or heavy industries produce CO₂ waste, technology can sometimes capture and store it.
Adaptation
Adaptation is "the process of adjusting to current or expected changes in climate and its effects." Without more efforts to reduce emissions, adaptation alone cannot stop the risk of "severe, widespread, and irreversible" impacts. More extreme climate changes require major changes in how people adapt, which can be very expensive. The ability and potential for humans to adapt vary widely across regions and populations, and developing countries usually have less capacity. In the first 20 years of the 21st century, most low- and middle-income countries saw some progress in improving access to basic sanitation and electricity, but this progress has been slow. Many countries have created policies to help with adaptation. However, there is a large gap between the money needed for adaptation 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 flood control systems. If these steps fail, moving people away from dangerous areas may be necessary. Economic challenges exist in addressing the effects of extreme heat. Avoiding heavy work or using air conditioning is not always possible for everyone. In agriculture, adaptation options include shifting to more sustainable food choices, growing a variety of crops, controlling soil erosion, and improving plant traits to better withstand climate changes. Insurance can help share risks, but it is often hard to obtain for people with low incomes. Education, migration, and early warning systems can reduce the risks people face from climate changes. Planting mangroves or other coastal plants can help protect against storms.
Ecosystems also adapt to climate changes, and humans can help this process. Connecting ecosystems allows species to move to areas with better climate conditions. Species can be moved to places that become more suitable as the climate changes. Protecting and restoring natural and semi-natural areas helps ecosystems become more resilient, making it easier for them to adapt. Many actions that help ecosystems adapt also help humans through methods like ecosystem-based adaptation. For example, restoring natural fire patterns reduces the chance of large fires and protects people. Giving rivers more space allows natural systems to store more water, reducing flood risks. Restored forests absorb carbon, but planting trees in areas unsuitable for them can worsen climate impacts.
Adaptation and efforts to reduce emissions can work together or create challenges. An example of working together is increasing food production, which benefits both adaptation and reducing emissions. A challenge is that using more air conditioning helps people cope with heat but increases energy use. Another challenge is that more compact city planning may reduce emissions from transportation and construction but can increase urban heat, raising health risks from heat.
Policies and politics
Countries most affected by climate change usually have contributed little to global emissions. This raises questions about fairness. Limiting global warming helps achieve the UN's Sustainable Development Goals, such as ending poverty and reducing inequality. Sustainable Development Goal 13 focuses on taking urgent action to fight climate change and its effects. Goals related to food, clean water, and protecting ecosystems work together with efforts to reduce emissions.
Climate change involves complex global relationships. It is often described as a "free-rider problem," where some countries benefit from others' efforts to reduce emissions but avoid making changes themselves. However, reducing emissions can also help local areas. For example, stopping coal use improves public health and the environment in most places. Countries that rely on imported fossil fuels benefit economically from 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 cut emissions. In 2019, carbon pricing covered about 20% of global greenhouse gas emissions. Carbon can be priced through taxes or trading systems. In 2017, direct fossil fuel subsidies 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 could support clean energy. Other methods include vehicle efficiency standards, renewable fuel rules, and pollution controls for heavy industries. Some countries require power companies to use more renewable energy. An Open Coalition on Compliance Carbon Markets was created at COP30 (2025) to build a global cap-and-trade system. This could increase emissions reductions seven times over current plans, provide $200 billion yearly for clean energy and social programs, and help meet the Paris Agreement goals.
Policies focused on climate justice aim to fix human rights and inequality issues. Supporters say those most responsible for climate change should pay for adaptation costs, while those suffering impacts should receive support. One way this happens is through wealthy nations funding poorer countries to adapt.
Oxfam found that in 2023, the wealthiest 10% of people caused 50% of global emissions, while the poorest 50% caused only 8%. Looking at production, the top 21 fossil fuel companies would owe $5.4 trillion in climate reparations from 2025 to 2050. A fair transition would provide new jobs for fossil fuel workers and invest in their communities.
Nearly all countries are part of the 1994 UN Framework Convention on Climate Change (UNFCCC). Its goal is to stop dangerous human harm to the climate system. It requires stabilizing greenhouse gas levels to protect ecosystems, food production, and economic growth. The UNFCCC does not set emission limits itself but creates rules for other agreements. Global emissions have risen since the UNFCCC began. Its yearly meetings are where global climate talks happen.
The 1997 Kyoto Protocol expanded the UNFCCC and required most developed countries to cut emissions. Developing nations, represented by the G77, pushed for developed countries to lead in reducing emissions because they contributed most to climate change. At the time, developing countries had lower per-person emissions and needed more emissions for growth.
The 2009 Copenhagen Accord was criticized for weak goals and rejected by poorer nations. It aimed to limit warming to below 2°C and promised $100 billion yearly for developing countries by 2020. A fund called the Green Climate Fund was created. By 2020, only $83.3 billion was delivered. The target was expected to be met in 2023.
In 2015, all UN countries agreed to the Paris Agreement, aiming to keep warming well below 2°C and ideally below 1.5°C. It replaced the Kyoto Protocol. Unlike Kyoto, the Paris Agreement does not set binding emission targets but requires countries to set increasingly ambitious goals every five years. It reaffirms that developing countries need financial support. As of March 2025, 194 countries and the European Union have joined the agreement.
The 1987 Montreal Protocol, which phased out ozone-depleting gases, also helped reduce climate change. Some of these gases are strong greenhouse gases, and banning them may have avoided a 0.5°C–1.0°C temperature rise. The 2016 Kigali Amendment aims to reduce emissions of hydrofluorocarbons, which are also powerful greenhouse gases. If followed, this could prevent an additional 0.3°C–0.5°C of warming.
In 2019, the UK became the first national government to declare a climate emergency. Other countries and regions followed. The same year, the European Parliament declared a "climate and environmental emergency." The European Commission introduced the European Green Deal, aiming for EU carbon neutrality by 2050. In 2021, the "Fit for 55" plan required all new cars in Europe to be zero-emission by 2035.
Major Asian countries have made similar pledges: South Korea, Japan, and China aim for carbon neutrality by 2050 and 2060, respectively. India supports renewable energy but plans to expand coal use. Vietnam, a coal-dependent developing country, pledged to phase out coal power by the 2040s or earlier.
As of 2021, based on 48 national climate plans covering 40% of Paris Agreement parties, estimated total greenhouse gas emissions would be 0.5% lower than 2010 levels. This is below the 45% or 25% reductions needed to limit warming to 1.5°C or 2°C, respectively.
Society and culture
Public debate about climate change has been influenced by people who deny or spread false information about it. This started in the United States and later spread to countries like Canada and Australia. These groups include fossil fuel companies, industry organizations, conservative think tanks, and scientists who disagree with mainstream scientific findings. Similar to the tobacco industry, these groups often create doubt about scientific evidence related to climate change. People who question the reality of climate change are sometimes called "skeptics," but more accurate terms are "contrarians" or "deniers."
There are different types of climate denial. Some people deny that Earth is warming at all. Others say warming is caused by natural factors, not human activity. Some downplay the harmful effects of climate change. Over time, creating doubt about climate science led to fake debates, making people believe scientists disagree about climate change when they actually do not. These groups often criticize scientific organizations and question scientists' motives. Websites and media that share climate denial ideas have made it harder for people to understand the real science.
Climate change became widely known internationally in the late 1980s. In the 1990s, media coverage sometimes confused climate change with other environmental issues, like the thinning of the ozone layer. Popular movies and documentaries, such as The Day After Tomorrow (2004) and An Inconvenient Truth (2006), helped bring climate change into public focus.
People’s concern and understanding of climate change vary by region, gender, age, and political views. More educated individuals, women, and younger people in some countries are more likely to see climate change as a serious problem. Some college biology textbooks from the 2010s included less information about climate change than earlier textbooks. Political differences also affect how people view climate change, and countries that produce a lot of carbon dioxide often show less concern. Media coverage of protests has influenced public opinions and what aspects of climate change are discussed. People who are more worried about climate change are more likely to support policies that address it. By 2021, most people in 30 countries said they were very worried about climate change or saw it as a global emergency. A 2024 survey found that 89% of people worldwide wanted stronger political action on climate change, but many underestimated how willing others were to act.
Climate protests push political leaders to take action against climate change. These protests can include public demonstrations, stopping investments in fossil fuels, lawsuits, and other activities. One well-known protest is the School Strike for Climate, where students worldwide skipped school on Fridays starting in 2018, inspired by Swedish activist Greta Thunberg. Groups like Extinction Rebellion have also organized large protests, such as blocking roads and public transportation.
Lawsuits are increasingly used to pressure governments and companies to act on climate change. Activists often file lawsuits against governments, demanding stronger action or enforcement of 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 action to stop climate change. If they fail to do so, other countries can legally challenge them. This includes following international agreements like the 2015 Paris Climate Accord.
History
In the 19th century, scientists like Alexander von Humboldt began to understand the effects of climate change. In the 1820s, Joseph Fourier explained the greenhouse effect, which showed why Earth's temperature was higher than sunlight alone could explain. Earth's atmosphere allows sunlight to reach the surface, where it becomes heat. However, the atmosphere does not allow all heat to escape, trapping some of it and warming the planet. In 1856, Eunice Newton Foote showed that air with water vapor warms more than dry air, and that carbon dioxide (CO₂) has an even stronger warming effect. She wrote that an atmosphere with this gas could make Earth very hot.
Starting in 1859, John Tyndall found that nitrogen and oxygen, which make up 99% of dry air, let heat pass through. However, water vapor and gases like methane and CO₂ absorb heat and send it back into the atmosphere. Tyndall suggested that changes in these gases might have caused past climate changes, such as ice ages.
Svante Arrhenius noted that water vapor levels change often, but CO₂ levels are affected by long-term geological processes. He explained that more CO₂ could increase water vapor, creating a cycle where warming leads to more warming. In 1896, Arrhenius created the first climate model, predicting that cutting CO₂ in half could cause an ice age. He estimated that doubling CO₂ could raise Earth’s temperature by about 5–6°C. Some scientists were skeptical at first, thinking the greenhouse effect was already complete and that the climate would balance itself. Beginning in 1938, Guy Stewart Callendar shared evidence that Earth was warming and CO₂ levels were rising, but his findings faced similar doubts.
In the 1950s, Gilbert Plass made a detailed computer model that studied different layers of the atmosphere and how heat is absorbed. This model predicted that rising CO₂ levels would cause warming. Around the same time, Hans Suess found proof that CO₂ levels were increasing, and Roger Revelle showed that oceans could not absorb all the extra CO₂. These scientists helped Charles Keeling start a long-term record of CO₂ levels, called the "Keeling Curve," which continued research into human causes of global warming. Studies like the National Research Council’s 1979 Charney Report supported climate models that predicted major warming. In 1988, James Hansen told a US Senate committee that human activity was causing global warming, and that this warming could be dangerous. The Intergovernmental Panel on Climate Change (IPCC), created in 1988, helped scientists work together to study climate change. Scientists in IPCC reports review research published in scientific journals.
Today, nearly all scientists agree that Earth is warming, and that humans are the main cause. No major scientific group disagrees with this. By 2019, more than 99% of recent scientific studies supported this view. The 2021 IPCC report said it is "unequivocal" that humans cause climate change. Scientists now agree that action is needed to protect people from climate change’s effects. 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 study how human-caused climate change affects the frequency, strength, and effects of extreme weather events. For example, scientists might say, "This weather event was at least n times more likely because of climate change" or "This heatwave was m degrees hotter than it would have been without global warming."
In the 2000s, better computers and new scientific ideas helped EEA study climate change’s effects on weather events with confidence. Scientists use methods and models that have already been checked by experts, allowing quick studies to be published soon after weather events happen.