Climate change

Climate change describes persistent shifts in the statistical pattern of weather over decades or longer. Natural factors include volcanic eruptions, changes in solar output, ocean circulation, and orbital cycles, but they do not explain the rapid warming observed since the mid-20th century.¹

Greenhouse gases absorb outgoing infrared radiation and warm the lower atmosphere and surface. Carbon dioxide from coal, oil, and gas is the largest contributor to current warming; methane, nitrous oxide, and industrial gases also matter. The ocean absorbs most of the excess heat, while melting ice and warming seawater raise global sea level.²

Climate differs from weather: a single cold winter does not disprove long-term warming, just as one hot day does not establish it. Climate scientists identify trends using observations, physical models, paleoclimate evidence, and attribution studies.

Human influence has unequivocally warmed the atmosphere, ocean, and land. Global surface temperature has risen by about 1.1°C in the 2011–2020 decade compared with 1850–1900, with warming occurring faster over land and in the Arctic.¹

Observed consequences include retreating glaciers, declining Arctic sea ice, loss of snow cover, ocean acidification, and rising sea levels. Heatwaves have become more frequent and intense in many regions, while heavy precipitation has increased in numerous areas; drought, wildfire weather, and tropical-cyclone impacts vary by location and by the particular hazard.³

Fossil-fuel combustion, cement production, land clearing, livestock, rice cultivation, fertilizers, and waste collectively increase atmospheric greenhouse-gas concentrations. Human-caused aerosols partly offset warming in some regions, but their cooling effect is temporary and uneven.

Climate change affects ecosystems, food production, water security, health, infrastructure, and economies, with risks increasing as warming intensifies. Vulnerability is shaped not only by exposure but also by poverty, governance, public health, geography, and access to adaptation resources.⁴

Mitigation reduces the causes of warming through measures such as renewable electricity, energy efficiency, electrification, methane control, protection and restoration of ecosystems, and changes in transport, buildings, industry, and food systems. Reaching net-zero carbon dioxide emissions is required to halt long-term human-caused warming, although some effects—especially sea-level rise—will persist for centuries.

Adaptation reduces harm through heat-health plans, flood defenses, drought-resistant crops, water management, early-warning systems, resilient buildings, and managed retreat where necessary. Adaptation has limits, particularly for coral reefs, low-lying coasts, and communities lacking finance or institutional capacity.⁴

Climate change is not geographically uniform: the Arctic is warming much faster than the global average, while some ocean regions experience different trends because of circulation and heat uptake. Urban areas can intensify heat through the urban heat-island effect, making local planning important even when regional averages appear moderate.

Some climate responses produce rapid benefits alongside slower climate gains. Cutting methane can reduce near-term warming, and reducing soot can improve air quality, although aerosol reductions that remove a cooling influence may reveal additional warming. Carbon dioxide removal may help balance residual emissions, but it cannot substitute for deep emissions cuts and carries ecological, land-use, and governance risks.⁵

Climate attribution increasingly distinguishes the human contribution to individual events rather than asking whether humans caused an event outright. International policy is organized chiefly through the United Nations Framework Convention on Climate Change and the Paris Agreement, whose goals include limiting warming well below 2°C and pursuing efforts toward 1.5°C.⁶

Greenhouse gas

A gas that absorbs and emits infrared radiation, contributing to warming of the atmosphere.

Mitigation

Action that reduces greenhouse-gas emissions or increases their removal from the atmosphere.

Adaptation

Adjustment of human or natural systems to actual or expected climate effects.

Climate attribution

Scientific analysis estimating how human influence changed the likelihood or intensity of an observed climate event.

Ocean acidification

The decrease in seawater pH caused mainly by ocean absorption of atmospheric carbon dioxide.