What Is Climate Change?

Climate change refers to long-term shifts in global and regional temperature, precipitation, wind patterns, and related atmospheric and oceanic conditions driven primarily by the accumulation of greenhouse gases in the atmosphere. In contemporary scientific usage the term most often designates the anthropogenic warming trend that has accelerated since the mid-twentieth century as a result of fossil fuel combustion, land-use change, and industrial emissions of carbon dioxide, methane, nitrous oxide, and other radiatively active gases.

The study of climate change draws on atmospheric physics, oceanography, geoscience, and ecology, and is informed by observational records from weather stations, ocean buoys, satellites, ice cores, and tree rings. Engineering disciplines contribute to both the understanding of climate dynamics, through the development of Earth system models and observational instruments, and to the responses it demands, through the design of low-carbon energy systems, resilient infrastructure, and carbon capture technologies.

Physical Mechanisms and Drivers

The greenhouse effect is the fundamental physical mechanism underlying anthropogenic climate change. Solar radiation enters the atmosphere and warms the Earth's surface; the surface re-emits energy as infrared radiation, which greenhouse gases absorb and re-radiate in all directions, including back toward the surface. Pre-industrial concentrations of atmospheric carbon dioxide were approximately 280 parts per million; by 2024 they exceeded 420 parts per million, a level not seen in at least three million years.

The IPCC Sixth Assessment Report synthesizes thousands of peer-reviewed studies and concludes that human influence has warmed the climate system at a rate unprecedented in at least the past two thousand years. Global average surface temperature has risen approximately 1.1 degrees Celsius above the 1850 to 1900 baseline. Feedback mechanisms amplify the initial warming: melting sea ice reduces surface albedo, increasing heat absorption; warming oceans release dissolved carbon dioxide; and thawing permafrost emits methane and carbon dioxide previously frozen in arctic soils.

Observed and Projected Impacts

Observed consequences of the warming trend include rising sea levels, shifts in precipitation patterns, more frequent and intense heat events, changes in the timing of seasonal biological events, and increased ocean acidity from carbon dioxide absorption. The IPCC projects that at 1.5 degrees Celsius of global warming, extreme heat events that previously occurred once per decade will occur approximately 4.1 times per decade; at 2 degrees Celsius, that frequency rises to 5.6 times. Sea level rise will continue for centuries owing to the thermal expansion of ocean water and the loss of mass from glaciers and ice sheets, regardless of near-term emissions reductions.

The IPCC Working Group II report on impacts, adaptation and vulnerability documents regional disparities in impact severity, with low-latitude, coastal, and least-developed regions facing the greatest risks. Ecosystem disruption, food and water security stress, and increased exposure to vector-borne diseases compound the direct physical hazards.

Mitigation and Adaptation

Mitigation refers to actions that reduce greenhouse gas emissions or enhance carbon sinks, thereby slowing the rate of warming. The primary mitigation pathways identified by the IPCC include rapid decarbonization of electricity generation through renewables and nuclear power, electrification of transportation and industrial heat, improvements in energy efficiency, and land-use changes that preserve forests and restore degraded carbon sinks. Carbon dioxide removal methods, including bioenergy with carbon capture and storage (BECCS) and direct air capture, are under active research and development. NOAA's National Centers for Environmental Information maintains the observational temperature records that track progress against mitigation targets.

Adaptation refers to adjustments in human and natural systems to reduce vulnerability to current and projected climate impacts. This includes flood defense infrastructure, drought-resistant crop varieties, early warning systems for extreme weather events, and urban planning that accounts for increased heat and precipitation intensity.

Applications

Climate change research and response connects to a wide range of engineering and scientific fields, including:

• Renewable energy systems engineering and grid integration
• Sea-level rise modeling and coastal infrastructure design
• Agricultural technology for climate-resilient crop production
• Carbon capture and sequestration technology development
• Climate modeling and Earth observation satellite systems
• Disaster risk reduction and emergency management systems