What Is Global Warming?

Global warming is the long-term increase in Earth's average surface temperature resulting primarily from the accumulation of greenhouse gases in the atmosphere due to human activities. The Intergovernmental Panel on Climate Change (IPCC) defines global warming formally as the estimated increase in global mean surface temperature averaged over a 30-year period, expressed relative to pre-industrial levels, which serves as the baseline for international policy targets. By the 2011–2020 decade, the IPCC's Sixth Assessment Report found that global surface temperature had already risen approximately 1.1°C above the 1850–1900 pre-industrial reference period, driven principally by fossil fuel combustion, deforestation, and industrial processes.

Global warming is distinct from climate change in that it refers specifically to the temperature dimension, while climate change encompasses the full suite of alterations in precipitation patterns, extreme event frequency, sea level, and ecosystem function that accompany warming. Research published by the IPCC characterizes the current warming as widespread, rapid, and intensifying, with human influence unequivocally established as the dominant driver.

The Greenhouse Effect

The greenhouse effect is the physical mechanism that converts rising concentrations of trace gases into surface warming. Solar radiation in the ultraviolet and visible spectrum passes largely unimpeded through the atmosphere and warms the Earth's surface, which re-emits energy as longer-wavelength infrared radiation. Greenhouse gases, including carbon dioxide (CO₂), methane (CH₄), nitrous oxide (N₂O), and water vapor, absorb this infrared radiation and re-emit it in all directions, including back toward the surface. This absorption reduces the rate at which energy escapes to space, creating a net radiative forcing that warms the lower atmosphere. The enhanced greenhouse effect refers to the intensification of this natural process caused by anthropogenic emissions, which have raised atmospheric CO₂ from approximately 280 ppm in the pre-industrial era to more than 420 ppm as of recent years, a concentration not seen in at least 800,000 years of ice-core records. The U.S. EPA's overview of greenhouse gases documents the global warming potential (GWP) of each major gas, with methane at 80 times the GWP of CO₂ over a 20-year horizon.

Atmospheric and Surface Temperature Measurements

Quantifying global warming requires integrating temperature records from multiple observing systems. Land surface temperature is measured by a network of ground-based weather stations maintained by national meteorological services and aggregated into global datasets by NOAA, NASA, and the UK Met Office. Ocean temperature accounts for more than 90% of the excess heat accumulating in the climate system and is measured through a network of Argo floats, ship-based profilers, and satellite-derived sea surface temperature products. Upper-atmosphere temperature trends are tracked by radiosondes and satellite-based microwave sounding units. NOAA's climate temperature monitoring synthesizes these land and ocean records into the global mean surface temperature anomaly time series that forms the primary metric for tracking global warming against pre-industrial baselines.

Carbon Emissions and Sequestration

Managing global warming requires understanding both the sources and sinks of greenhouse gases. Carbon emissions arise from fossil fuel combustion, cement production, agricultural practices, and land-use change, with the energy sector accounting for the largest share. Carbon sequestration encompasses the natural processes by which CO₂ is removed from the atmosphere, primarily through ocean uptake and terrestrial photosynthesis, as well as engineered approaches such as bioenergy with carbon capture and storage (BECCS) and direct air capture. The balance between emissions and sequestration determines whether atmospheric CO₂ concentrations rise or stabilize, making carbon accounting central to energy informatics and climate policy modeling.

Applications

Research on global warming has applications in a wide range of disciplines, including:

• Climate adaptation engineering for infrastructure exposed to changing temperature and precipitation extremes
• Energy systems planning to reduce carbon emissions and integrate renewable sources
• Agricultural modeling to anticipate shifts in growing seasons and crop stress thresholds
• Coastal and flood risk management in response to sea level rise projections
• Air quality management, since many warming-driven changes also affect ground-level ozone and particulate matter concentrations