6 Climate Change
Understand how Earth's climate system works, why human activities are driving recent warming, how climate risks affect people and ecosystems, and how mitigation and adaptation can address those risks.
Earth’s system
Earth’s is the long-term pattern of temperature, precipitation, winds, and other conditions. Weather describes short-term conditions, while describes patterns over decades or longer. A cold day or a single storm does not, by itself, show whether the is changing.
The system arises from interactions among the atmosphere, oceans, land, ice, and living things. The Sun supplies energy; Earth reflects some of it and releases the rest as heat. Naturally occurring greenhouse gases, including water vapor, carbon dioxide, and methane, absorb some outgoing heat and keep the planet warm enough for life. This natural is essential, but adding more heat-trapping gases strengthens it and changes the system.
Scientists assess long-term observations alongside evidence from sources such as ice cores, tree rings, and ocean sediments.
Human influence and global warming
Human activities—especially burning coal, oil, and natural gas; clearing forests; and some agricultural and industrial processes—increase atmospheric greenhouse gases. These gases trap additional heat. Natural factors, including volcanic eruptions and changes in solar output, also affect , but they cannot explain the warming observed since the mid-20th century. The IPCC concludes that human influence has unequivocally caused global warming.
In 2011–2020, global surface temperature was about above its 1850–1900 average. Warming is global, but its effects vary by region.
The system has inertia: oceans absorb and store heat, so some changes continue even after emissions fall. The amount of future warming depends largely on future greenhouse-gas emissions.
Impacts on people and nature
A warmer changes average conditions and affects the likelihood or severity of some extremes. Observed and projected impacts include more intense heat in many regions, changes in rainfall and drought risk, shrinking glaciers, rising seas, and stress on ecosystems.
hazards can damage crops, infrastructure, and homes, and threaten health and water supplies. Specific risks depend on local exposure and . For example, coastal communities face flooding risks from sea-level rise, while farmers may face heat or shifts in seasonal rainfall.
Impacts are unequal. Communities with fewer resources to prepare, respond, and recover often face greater risks, even though their historical contribution to emissions may be relatively small. change also interacts with other pressures, including habitat loss, pollution, and overuse of natural resources. Protecting biodiversity and healthy ecosystems can support both people and nature.
and
limits change by reducing greenhouse-gas emissions or increasing their removal from the atmosphere. Examples include replacing fossil fuels with low- or zero-emission energy, improving energy efficiency, reducing deforestation, and restoring forests and wetlands. Because carbon dioxide accumulates, cutting emissions reduces the additional warming humans cause. Rapid, sustained reductions are needed to limit future warming.
means adjusting to actual or expected impacts to reduce harm or make use of possible benefits. Examples include heat-warning systems, urban shade, water conservation, flood planning, and crop varieties suited to changing conditions. can reduce risks, but it cannot prevent all harm, and its effectiveness has limits.
and work best together. Restoring a wetland, for example, can store carbon, provide wildlife habitat, and help absorb floodwater. Effective responses combine technology, planning, ecosystem protection, and fair access to resources. Choices made by governments, businesses, communities, and individuals shape both emissions and resilience.
Key takeaways
Earth’s is governed by interactions among the atmosphere, oceans, land, ice, and life, with greenhouse gases helping regulate heat. Human activities have strengthened the and are the main cause of recent global warming. The resulting risks affect people and ecosystems unevenly. limits the causes of change, while reduces to its impacts. Both are important for a sustainable and -resilient future.