Climate change is the long-term shift in Earth’s temperatures and weather patterns. Although the planet’s climate has changed naturally throughout its history, the rapid warming observed since the industrial era is primarily caused by human activities, especially the burning of fossil fuels. These activities increase the concentration of heat-trapping gases in the atmosphere, warming the planet and altering weather patterns, oceans, ecosystems, and human communities.
Climate change is not simply a matter of warmer days. It affects how much moisture the atmosphere holds, how frequently certain types of extreme weather occur, how quickly ice melts, and how high sea levels rise. Understanding its causes, the evidence supporting it, and its consequences helps explain why it has become one of the most important environmental and public health challenges facing the United States and the world.
What climate change means
Earth’s climate describes the long-term patterns of temperature, precipitation, wind, humidity, and other atmospheric and oceanic conditions. Weather refers to what happens over hours or days, while climate describes the patterns and averages observed over decades or longer.
Climate change occurs when these long-term patterns shift. A region might experience changes in its typical winter temperatures, the timing of spring rainfall, the length of its growing season, or the frequency of heat waves. Globally, climate change can alter the average temperature of the planet and the distribution of heat and moisture across its surface.
The terms climate change and global warming are related, but they do not mean exactly the same thing. Global warming refers specifically to the long-term rise in Earth’s average surface temperature. Climate change encompasses global warming and its wider effects, including changes in precipitation, ocean circulation, ice cover, sea level, and extreme weather patterns.
Climate has never been completely stable. Volcanic eruptions, variations in the Sun’s energy, changes in Earth’s orbit, and shifts in the distribution of heat by oceans and the atmosphere have influenced climate throughout geological history. The defining feature of modern climate change is that human activities have become the dominant cause of the current long-term global warming.
How Earth’s climate system works
Earth receives energy from the Sun, primarily as visible light and other forms of shortwave radiation. Some of this energy is reflected into space by clouds, atmospheric particles, ice, and other bright surfaces. The rest is absorbed by the land, oceans, and atmosphere, warming the planet.
Earth also releases energy back toward space as infrared radiation, commonly described as heat. Certain atmospheric gases absorb some of this outgoing radiation and emit energy in different directions, including back toward the surface. This natural process, known as the greenhouse effect, keeps Earth considerably warmer than it would otherwise be and makes the planet habitable for life as we know it.
The main heat-trapping gases include water vapor, carbon dioxide, methane, nitrous oxide, and certain industrial gases. Each absorbs infrared radiation at particular wavelengths, making it harder for the Earth system to release energy directly into space.
The natural greenhouse effect is essential to life. The problem arises when human activities increase the concentrations of greenhouse gases, strengthening this effect and disrupting the planet’s energy balance.
When Earth retains more energy than it releases, the climate system warms. The additional energy does not remain solely in the air. The oceans absorb much of it, while the land, atmosphere, and melting ice also respond. These interconnected processes help explain why climate change affects so many parts of the Earth system and why its effects can continue long after emissions occur.
What causes climate change?
Natural processes and human activities can both change the climate, but they do not contribute equally to present-day global warming. Scientific understanding of modern climate change rests on identifying the forces that affect Earth’s energy balance and comparing their expected effects with the changes actually observed.
Burning fossil fuels
The largest driver of current human-caused climate change is the burning of coal, oil, and natural gas. These fuels contain carbon that has been stored underground for millions of years. When burned for electricity, transportation, heating, manufacturing, and other purposes, they release carbon dioxide into the atmosphere.
Carbon dioxide is especially important because it accumulates over time. Natural processes, including plant growth and ocean absorption, remove some of the carbon dioxide humans release, but they do not absorb all of it. As a result, atmospheric concentrations rise, strengthening the greenhouse effect.
The effects extend beyond power plants and vehicle exhaust. Producing cement, manufacturing materials, generating industrial heat, and operating buildings can all contribute to fossil fuel emissions, directly or indirectly.
Reducing these emissions is central to limiting additional global warming.
Deforestation and land-use changes
Forests and other ecosystems absorb carbon dioxide through photosynthesis, the process by which plants use sunlight to convert carbon dioxide and water into sugars and release oxygen. Much of the carbon absorbed by plants becomes stored in vegetation, roots, and soil.
When forests are cleared or burned, some of this stored carbon returns to the atmosphere. Removing forests also reduces the amount of carbon dioxide that the land can absorb in the future. Changes in land cover can further influence how much sunlight a surface reflects, how water moves through an ecosystem, and how energy is exchanged between the land and atmosphere.
Agriculture, urban development, and the conversion of natural landscapes can therefore affect climate in several ways. Their effects vary according to the type of land, the previous ecosystem, and how the land is managed.
Methane and other greenhouse gases
Carbon dioxide is not the only gas responsible for human-caused warming. Methane is released by sources such as livestock digestion, landfills, fossil fuel production, and leaks from natural gas infrastructure. It is more effective than carbon dioxide at trapping heat over a given period, molecule for molecule, but it remains in the atmosphere for a much shorter time.
This difference matters. Reducing methane emissions can slow the rate of warming relatively quickly, while reducing carbon dioxide emissions is essential to limiting the long-term accumulation of heat-trapping carbon.
Nitrous oxide, associated with agricultural soils, fertilizers, industrial processes, and some combustion, also contributes to warming. Certain synthetic gases used in industrial applications and refrigeration can have substantial heat-trapping effects even when emitted in comparatively small quantities.
These gases differ in their atmospheric lifetimes and their ability to absorb infrared radiation. Their combined influence determines a significant part of the human impact on Earth’s energy balance.
Natural influences on climate
Natural factors continue to affect climate, but they cannot explain the dominant pattern of modern global warming.
Changes in solar output can influence Earth’s temperature. However, the observed warming pattern does not match what would be expected if an increase in the Sun’s energy were the main cause.
Volcanic eruptions can inject reflective particles into the atmosphere, temporarily reducing the amount of sunlight reaching Earth’s surface and cooling the planet. These effects generally last for a limited period rather than producing the sustained warming observed over recent decades.
Ocean circulation also shifts heat between regions and between the ocean and atmosphere. These variations can make some places temporarily warmer or cooler and influence global temperatures from year to year. They redistribute heat, however, and do not account for the long-term accumulation of energy caused by increasing greenhouse gas concentrations.
Changes in Earth’s orbit and orientation have driven major natural climate shifts over geological time, including ice ages. Their influence unfolds over thousands to tens of thousands of years, making them an inadequate explanation for the speed and pattern of current warming.
What evidence shows that climate change is happening?
The evidence for modern climate change comes from multiple independent measurements. Thermometers, satellites, ocean instruments, ice records, and observations of ecosystems reveal changes that fit together into a consistent picture of a warming planet.
Rising global temperatures
Measurements from weather stations, ships, ocean buoys, and other instruments show a long-term rise in global average surface temperature. Although individual years vary, the broader trend is unmistakable: Earth has warmed substantially since the industrial era.
The warming is not identical everywhere. Land generally warms faster than the ocean, and some regions experience greater changes than others. Natural variations can also temporarily accelerate or slow the increase in global average temperature.
These differences do not undermine the global trend. Climate scientists evaluate temperature patterns across large areas and long periods to distinguish sustained change from ordinary fluctuations in weather.
Increasing greenhouse gas concentrations
Measurements of atmospheric composition show that carbon dioxide and several other greenhouse gases have increased markedly since industrialization. The chemical characteristics of the additional carbon dioxide provide evidence that much of it comes from fossil fuels and changes in land use.
For example, carbon released by fossil fuels has a distinctive isotopic signature, reflecting the composition of ancient organic material. Atmospheric oxygen measurements also provide evidence consistent with the consumption of oxygen during fossil fuel combustion.
These observations directly connect human activities to the rising concentration of atmospheric carbon dioxide. Laboratory measurements and established physical principles show that this increase strengthens the greenhouse effect.
Warming oceans
The oceans absorb most of the excess heat accumulating in the climate system. Measurements of ocean temperatures show that the ocean has gained substantial heat over time.
Ocean heat content is an important indicator because it is less sensitive than surface air temperature to short-term variations such as temporary shifts in atmospheric circulation. Even when global surface temperatures rise more slowly for a period, the oceans can continue accumulating energy.
As seawater warms, it expands. This process, called thermal expansion, contributes to sea-level rise. Ocean warming also affects marine ecosystems, oxygen levels in some waters, and the distribution of species.
Melting glaciers and shrinking ice
Glaciers in many mountain regions have lost mass as temperatures have risen. Satellite observations and other measurements also show a decline in the extent of Arctic sea ice over the long term, although its area continues to fluctuate seasonally and from year to year.
The Greenland and Antarctic ice sheets have also lost mass overall. Because these ice sheets contain enormous quantities of land-based ice, continued ice loss contributes to rising sea levels.
Not all ice has the same effect on sea level. Melting floating sea ice has little direct effect on sea level because it already displaces seawater. Melting land-based glaciers and ice sheets adds water to the ocean and therefore raises sea level.
Rising sea levels
Global mean sea level has risen as ocean water has expanded with warming and land-based ice has melted. Measurements from tide gauges and satellites document this rise.
The consequences vary by location. Local sea levels are also influenced by land sinking or rising, ocean currents, winds, and gravitational effects associated with large ice sheets. As a result, some coastlines experience faster sea-level rise than the global average.
Rising seas increase the risk of coastal flooding, worsen saltwater intrusion into freshwater systems, and allow storm surges to reach farther inland. Even modest increases can make flooding more frequent in low-lying coastal communities.
Changes in seasons and ecosystems
Climate change is also visible in the natural world. In many regions, spring events such as flowering and leaf emergence occur earlier than they once did. The geographic ranges of some species have shifted, and changes in water availability and temperature have affected the timing of migration, breeding, and other seasonal behaviors.
These biological responses are not uniform. Some species adapt or move successfully, while others struggle because suitable habitat disappears, migration routes are limited, or the pace of environmental change exceeds their ability to adjust.
No single observation proves the entire case for climate change. The strength of the evidence comes from the agreement among temperature records, atmospheric chemistry, ocean measurements, ice observations, sea levels, and ecological changes.
How scientists determine the causes of warming
Detecting a change in climate is only part of the scientific task. Researchers must also determine why it is happening.
Scientists use physical laws, observations, and climate models to examine how different influences affect Earth’s energy balance. They compare the expected patterns of greenhouse gas warming with the patterns measured in the real world.
One important piece of evidence is that the lower atmosphere is warming while the stratosphere, a higher atmospheric layer, has generally cooled. Increased greenhouse gases produce this pattern because they cause the lower atmosphere and surface to retain more heat while changing how energy escapes from higher layers.
Scientists also examine seasonal and geographic patterns, changes in the outgoing infrared radiation measured from space, and the increasing heat stored in the oceans. Together, these observations match the expected effects of rising greenhouse gas concentrations.
Climate models provide another line of evidence. These computer-based representations of the climate system use physical equations to simulate interactions among the atmosphere, oceans, land, ice, and incoming solar energy. Researchers can compare simulations that include human influences with simulations that include only natural influences.
When models include the increase in greenhouse gases from human activities, they reproduce the broad pattern of observed warming far more successfully than simulations that exclude those influences. This is a central reason scientists conclude that human activity is the primary cause of modern global warming.
Models are not perfect predictions of every future event. Their accuracy depends on the quality of their physical representations, the assumptions used, and future choices about emissions. Nevertheless, they are valuable tools for understanding the climate system and estimating how it may respond to different conditions.
How climate change affects weather and extreme events
Climate change does not mean that every place becomes hotter every day or that every storm is caused by global warming. Weather remains variable, and natural processes continue to influence individual events.
Instead, warming changes the conditions in which weather occurs. It can alter the probability, intensity, duration, or geographic distribution of certain types of extreme events.
Heat waves and extreme temperatures
As average temperatures rise, extreme heat becomes more likely and severe heat events generally become more intense. A heat wave that would once have been unusual can become more common in a warmer climate.
High temperatures increase the risk of heat exhaustion, heatstroke, and other health problems. They can also raise electricity demand for cooling, stress crops and livestock, and strain transportation systems and power infrastructure.
Nighttime temperatures matter as well. When nights remain unusually warm, people have fewer opportunities to recover from daytime heat, especially in homes without adequate cooling.
Heavy rainfall and flooding
Warmer air can hold more water vapor. As a result, a warmer atmosphere can provide more moisture for storms, increasing the potential for intense precipitation when conditions are favorable.
This does not mean that every region will receive more rain overall. Some places may experience longer dry periods, while others face heavier downpours. Changes in storm tracks, local geography, and atmospheric circulation influence the outcome.
Heavy rainfall can overwhelm drainage systems, cause flash floods, damage roads and buildings, and contaminate drinking-water supplies. Urban areas are particularly vulnerable where pavement and other impermeable surfaces prevent water from soaking into the ground.
Flood risk also depends on factors such as soil conditions, land development, drainage capacity, and the management of rivers and reservoirs. Climate change can increase the hazard, while local decisions strongly influence the resulting damage.
Drought and wildfire conditions
Climate change can increase drought risk in some regions by raising evaporation rates, drying soils, and increasing the water demand of plants. Changes in precipitation patterns may intensify these effects, although drought trends differ by region.
Hot, dry conditions can also increase the likelihood of severe wildfire weather. Dry vegetation provides fuel, and prolonged periods of heat and low humidity can make fires easier to ignite and harder to control.
Climate is only one part of wildfire risk. Ignition sources, forest management, vegetation, wind, development near wildlands, and firefighting conditions all matter. Climate change does not cause every wildfire, but it can create conditions that increase the potential for larger or more intense fires in vulnerable areas.
Hurricanes and other severe storms
Tropical cyclones, including hurricanes in the Atlantic, draw energy from warm ocean waters. Rising ocean temperatures can increase the potential for intense rainfall and contribute to the conditions that support stronger storms.
Sea-level rise also worsens coastal flooding associated with storm surge, the abnormal rise of seawater pushed toward shore by a storm. A storm of similar strength can therefore produce more damaging coastal flooding than it would have under lower sea levels.
The relationship between climate change and the total number of hurricanes is more complicated. Scientists do not expect every storm-related measure to change in the same direction, and natural variability remains important. The clearest concerns include heavier rainfall from tropical cyclones, worsening storm-surge impacts because of higher seas, and an increased potential for the strongest storms.
For individual weather events, scientists use attribution studies to estimate whether human-caused climate change altered the likelihood or intensity of the event. The answer varies by event type and location.
The impacts of climate change on people and ecosystems
Climate change affects natural systems and human societies through several connected pathways. Temperature, water availability, sea level, and extreme weather influence where people can live, what they can grow, how they maintain their health, and how ecosystems function.
Human health
Extreme heat is a direct health threat. It can cause heat-related illness, worsen existing medical conditions, and increase the risk of death, particularly among older adults, outdoor workers, young children, and people without reliable access to cooling.
Climate change can also affect health indirectly. Smoke from wildfires can worsen respiratory problems, while flooding can damage sanitation systems and create conditions that favor some waterborne diseases. Changes in temperature and precipitation can alter the geographic range and seasonal activity of disease-carrying organisms, including certain mosquitoes and ticks.
The effects are not limited to physical illness. Disasters, displacement, financial losses, and the disruption of familiar communities can contribute to psychological stress and other mental health challenges.
The severity of these impacts depends partly on public health systems, housing quality, access to medical care, local infrastructure, and the availability of early warnings.
Food production and water supplies
Agriculture depends on temperature, rainfall, soil moisture, growing seasons, and the availability of water. Climate change can affect all of these factors.
Moderate warming may extend growing seasons in some cooler regions, but higher temperatures and greater heat stress can reduce yields for many crops, especially when heat coincides with sensitive stages of plant development. Drought, heavy rainfall, shifting pest ranges, and changing soil conditions can create additional challenges.
The effects vary by crop and location. Farmers may adapt through changes in planting dates, crop varieties, irrigation, soil management, and other practices, but adaptation has limits when heat or water shortages become severe.
Water supplies face related pressures. Higher temperatures can increase evaporation, alter snow accumulation and melt, and change the timing of river flows. In regions that depend on mountain snowpack, less snow or earlier melting can reduce water availability during the hottest parts of the year.
Heavy rainfall does not automatically solve drought. Water that falls in intense downpours may run off quickly rather than replenishing soil moisture or groundwater, particularly where the ground is dry, compacted, or paved.
Oceans and marine life
Oceans are changing through warming, rising sea levels, and acidification. Ocean acidification occurs when seawater absorbs carbon dioxide from the atmosphere and chemical reactions reduce its pH, making the water more acidic.
The ocean is naturally slightly alkaline, so acidification does not mean that all seawater has become acidic in the everyday sense. Instead, it means the water is becoming less alkaline. This shift reduces the availability of carbonate ions that many marine organisms need to build shells and skeletons.
Corals, shellfish, and some plankton are especially sensitive to changes in ocean chemistry. Their responses vary, but continued acidification can make it harder for certain organisms to grow and maintain their structures.
Marine heat waves can also cause coral bleaching, a process in which corals lose the symbiotic algae that provide much of their energy. Bleaching does not always kill corals, but prolonged or repeated heat stress can lead to widespread mortality and damage reef ecosystems.
Warming oceans also influence where marine species can survive, with consequences for fisheries, food webs, and communities that depend on seafood for nutrition and income.
Wildlife and biodiversity
Species survive within environmental limits shaped by temperature, moisture, food availability, and habitat. As climate conditions change, many organisms shift their ranges toward cooler regions or higher elevations when suitable habitats and migration routes are available.
Other species may alter their seasonal behavior or adapt to new conditions. However, species that move slowly, depend on specialized habitats, or face fragmented landscapes may have fewer options.
Climate change can also intensify existing pressures, including habitat destruction, pollution, invasive species, and overexploitation. A species already under stress may be less able to withstand additional warming or changes in rainfall.
The consequences extend beyond individual species. Ecosystems depend on relationships among plants, animals, fungi, and microorganisms. Changes in one part of a food web can affect pollination, soil health, water quality, and the stability of the wider system.
Coastal communities and infrastructure
Sea-level rise threatens low-lying coastlines through more frequent flooding, shoreline erosion, and saltwater intrusion into freshwater aquifers. Coastal storms can cause particularly severe damage when elevated sea levels combine with storm surge and heavy rainfall.
The United States faces varied regional risks. Communities along the Atlantic and Gulf coasts must contend with coastal flooding and tropical storms, while parts of the West face challenges associated with heat, drought, wildfire, and changes in mountain snowpack. Alaska is experiencing effects related to warming, melting land ice, and the loss of protective sea ice in some coastal areas.
Infrastructure designed around historical climate conditions may become less reliable as extremes change. Roads can buckle under intense heat, electrical systems can struggle during periods of high demand, and drainage networks may be overwhelmed by heavy rainfall.
Preparing for these risks involves maintaining and upgrading infrastructure, protecting natural barriers where appropriate, improving building standards, and incorporating future climate conditions into long-term planning.
Why climate change affects communities unequally
Climate change is a global process, but its consequences are not evenly distributed. Geography, income, age, health, occupation, and access to public services all influence a person’s exposure and ability to recover.
People who work outdoors may face greater heat exposure than those who work in climate-controlled buildings. Households without reliable air conditioning, adequate insulation, or affordable electricity may be more vulnerable during heat waves. Communities in flood-prone areas may face repeated property damage, while people with limited financial resources may struggle to relocate or rebuild.
Some communities also have fewer resources for emergency response, healthcare, and infrastructure improvements. The same climate hazard can therefore produce very different outcomes depending on local conditions.
Climate change can also create economic pressures through crop losses, property damage, disruptions to transportation, and rising costs associated with disaster recovery and adaptation. The scale of these effects depends on the severity of the hazard, the exposure of people and assets, and the measures taken to reduce risk.
Understanding unequal vulnerability is essential for effective climate policy. Reducing emissions addresses the underlying cause of additional warming, while targeted preparation and investment can help protect people who face the greatest risks.
What scientists know and what remains uncertain
The central scientific conclusions about modern climate change are well established: Earth is warming, human activities are increasing greenhouse gas concentrations, and these increases are the primary cause of recent long-term global warming.
Uncertainty remains about the precise timing, magnitude, and local distribution of some future impacts. This uncertainty does not mean scientists lack confidence in the basic explanation. It reflects the complexity of the climate system and the influence of choices people make in the coming decades.
One major source of uncertainty is future greenhouse gas emissions. The amount of warming that occurs will depend substantially on how much carbon dioxide and other heat-trapping gases humanity releases and how quickly emissions decline.
Another source is regional climate behavior. Global models can estimate broad trends with greater confidence than they can predict the exact rainfall changes or extreme-weather patterns for every individual community. Local geography, ocean circulation, and natural variability complicate regional projections.
Some processes also introduce uncertainty into estimates of future ice loss, ecosystem responses, and changes in extreme events. These uncertainties can affect how quickly particular risks emerge and how severe they become.
Scientists express projections using ranges and scenarios rather than a single guaranteed outcome. Scenarios describe possible future pathways based on assumptions about emissions, technology, economic development, and other factors. They are not necessarily predictions of what will happen; they show how climate outcomes depend on different choices and conditions.
Importantly, uncertainty can work in both directions. Some impacts may be less severe than expected, while others may occur faster or prove more damaging. Good planning considers a range of plausible outcomes rather than assuming that the least harmful possibility will occur.
How climate change can be limited
Climate change can be addressed through two complementary approaches: mitigation and adaptation.
Mitigation means reducing the causes of climate change by limiting greenhouse gas emissions or increasing the removal of carbon dioxide from the atmosphere. Adaptation means adjusting human systems and natural environments to reduce harm from climate impacts that are already occurring or expected.
Neither approach can fully replace the other. Mitigation limits the amount of additional warming, while adaptation helps communities manage risks that cannot be avoided.
Reducing greenhouse gas emissions
A major mitigation strategy is replacing fossil fuels with energy sources that produce little or no greenhouse gas emissions during operation, including wind, solar, nuclear, and hydropower. The best combination varies according to geography, infrastructure, cost, reliability, and other local conditions.
Improving energy efficiency also reduces emissions by lowering the amount of energy needed for heating, cooling, transportation, and industrial activity. Better building insulation, efficient appliances, improved industrial processes, and more efficient vehicles can all help.
Transportation can become less emissions-intensive through electrification, cleaner electricity, public transit, walking, cycling, and more efficient freight systems. The overall benefits depend on how vehicles and infrastructure are manufactured and how the electricity or fuels they use are produced.
Reducing methane leaks from fossil fuel systems, improving waste management, and changing certain agricultural practices can further limit warming. Protecting forests and restoring damaged ecosystems can preserve carbon stores and support biodiversity, although land-based carbon storage is vulnerable to fire, drought, and future land-use changes.
Carbon removal technologies can also help take carbon dioxide out of the atmosphere, but their cost, energy requirements, scalability, and long-term storage reliability vary. They do not eliminate the need to reduce emissions at their source.
Because carbon dioxide persists in the climate system over long periods, achieving net-zero carbon dioxide emissions is central to stopping further long-term warming from carbon dioxide. Net zero means that remaining human-caused emissions are balanced by removals. It does not mean that the atmosphere immediately returns to its earlier composition or that all climate impacts stop.
Preparing for unavoidable impacts
Adaptation includes measures such as expanding access to cooling during heat waves, improving flood defenses, restoring wetlands, reducing wildfire exposure, updating building codes, and strengthening emergency warning systems.
Farmers can adjust crop choices and planting schedules, improve soil moisture retention, and use irrigation more efficiently where water resources allow. Cities can reduce heat exposure by increasing shade, planting suitable vegetation, and designing buildings and public spaces to manage high temperatures.
Coastal communities may protect shorelines, elevate vulnerable infrastructure, improve drainage, restore natural barriers, or move development away from areas facing severe and recurring flood risks. The appropriate response depends on local conditions, expected future hazards, environmental effects, and available resources.
Adaptation has limits. Some changes can be managed through better planning and investment, but others may become increasingly difficult or expensive as warming intensifies. This is why reducing future emissions remains essential even as societies prepare for the impacts of a changing climate.
The role of individuals, communities, and governments
Individuals can contribute by improving household energy efficiency, choosing lower-emissions transportation when practical, reducing food waste, and supporting measures that cut emissions. The opportunities available to each person depend on income, location, infrastructure, and personal circumstances.
However, climate change cannot be solved through individual choices alone. Electricity systems, transportation networks, building standards, industrial technologies, agricultural practices, and land-use decisions are shaped by institutions, businesses, and public policy.
Governments can establish emissions standards, invest in cleaner energy and resilient infrastructure, protect ecosystems, and support research and technological development. Businesses can reduce emissions across their operations and supply chains, while communities can incorporate climate risks into planning and emergency preparedness.
Effective action combines these efforts. Reducing greenhouse gas emissions addresses the main driver of modern climate change, and well-designed adaptation measures help protect people and ecosystems from the consequences that can no longer be avoided.
Why the timing of climate action matters
The climate system responds gradually to changes in energy balance, but the effects of emissions accumulate. Carbon dioxide released today can influence the climate for centuries, while some of the heat absorbed by the oceans can continue affecting the climate long after emissions decline.
This delay means that reducing emissions does not instantly reverse warming. It does, however, limit the additional greenhouse gases that accumulate and reduce the amount of future warming that would otherwise occur.
The distinction between current impacts and future risks is important. Some changes, including certain forms of ice loss and sea-level rise, continue over long periods because of the slow response of oceans and ice sheets. Other risks, such as the frequency of extreme heat, respond more directly to the amount of additional warming.
Every increment of warming matters because risks generally increase as global temperatures rise. More warming tends to intensify heat extremes, increase the potential for heavy precipitation in many regions, worsen some drought risks, and raise long-term sea levels. The exact effects differ by location, but limiting warming reduces many of these risks.
Climate change is therefore neither a problem that can be solved instantly nor one whose outcome is already completely determined. Human activities have driven the current warming, and future emissions will strongly influence how much further the climate changes.
The scientific evidence provides a clear basis for understanding the problem: greenhouse gases alter Earth’s energy balance, the resulting warming affects the entire climate system, and the consequences reach far beyond average temperature. Reducing emissions can limit future change, while preparation and adaptation can help communities manage the impacts of a warming world.
