Earth’s energy budget is the accounting of energy entering, leaving, and moving within Earth’s climate system. Its main external components are incoming radiation from the Sun, reflected sunlight, and thermal radiation emitted to space. Exchanges among the surface, atmosphere, and oceans determine how absorbed energy is redistributed and stored. A persistent difference between incoming and outgoing energy changes the system’s heat content and is fundamental to understanding climate change. (ceres.larc.nasa.gov)
Incoming sunlight and planetary balance
Solar energy arrives as electromagnetic radiation, principally at visible and near-infrared wavelengths. At Earth’s average distance from the Sun, the power received by a surface perpendicular to the sunlight is approximately 1,360 watts per square meter. Averaged over the entire spherical planet, this becomes about 340 W/m²: Earth intercepts sunlight across a disk, but its total surface area is four times that disk’s area. (science.nasa.gov)
About 29–30% of incoming sunlight returns to space through reflection by clouds, atmospheric particles, and the surface. This reflected fraction is called planetary albedo. The remaining approximately 240 W/m² is absorbed by the atmosphere and surface. These are rounded global averages, not values applying everywhere or at every moment. (science.nasa.gov)
The global top-of-atmosphere radiation balance can be written as
where is net downward energy flux, is total solar irradiance, is planetary albedo, and OLR is outgoing longwave radiation. Positive indicates energy accumulation; negative indicates energy loss. Radiative equilibrium corresponds to , although individual regions and components need not be in balance. (ipcc.ch)
Thermal radiation and the greenhouse effect
Because Earth is much cooler than the Sun, its emitted radiation lies mainly in the thermal infrared. The greenhouse effect arises because greenhouse gases, including water vapor and carbon dioxide, absorb and emit infrared radiation at particular wavelengths. The atmosphere emits both upward toward space and downward toward the surface. This downward radiation helps maintain a warmer surface than direct solar heating alone would produce. (gml.noaa.gov)
Some surface radiation escapes through relatively transparent wavelength ranges known as the atmospheric window. Much is absorbed within the atmosphere, so radiation leaving the planet originates from both the surface and atmospheric layers. Surface emission therefore cannot be equated with outgoing radiation measured above the atmosphere. (prod-01-alb-www-noaa.woc.noaa.gov)
Clouds influence both sides of this balance: they reflect sunlight, producing a cooling contribution, and impede outgoing infrared radiation, producing a warming contribution. Their net effect depends on their properties and distribution. Satellite comparisons of cloudy and clear conditions help quantify this cloud radiative effect. (gfdl.noaa.gov)
Surface and atmospheric exchanges
The surface absorbs roughly half of incoming solar radiation. It also receives atmospheric infrared radiation and loses energy through thermal emission and nonradiative transfers. Globally averaged, the surface has a net radiative gain, whereas the atmosphere has a net radiative loss; transfers between them help offset these differences. (ceres.larc.nasa.gov)
Latent heat transfer occurs when water evaporates, removing energy from the surface. Condensation subsequently releases that energy into the atmosphere. Sensible heat transfer warms the air through contact with the surface and turbulent transport. These exchanges connect the energy budget with the water cycle and atmospheric motion. Consequently, a surface budget must include more than radiation alone. (ceres.larc.nasa.gov)
Large opposing infrared fluxes between the atmosphere and surface do not constitute additional external energy. They represent internal exchanges; their difference, together with solar absorption and nonradiative transfers, determines net surface heating or cooling. (prod-01-alb-www-noaa.woc.noaa.gov)
Geographic redistribution
The global mean conceals substantial geographic differences. In annual averages, tropical regions generally absorb more solar energy than they emit to space, while polar regions experience a radiative deficit. Atmospheric and oceanic circulations transport energy between these regions, connecting local energy balances to planetary climate. (ceres.larc.nasa.gov)
Regional budgets therefore include horizontal energy transport as well as radiation and storage. A region can remain approximately stable despite a sustained radiative surplus if circulation exports the excess. Global equilibrium does not require local equilibrium or an absence of circulation. (ceres.larc.nasa.gov)
Energy imbalance and heat storage
The Intergovernmental Panel on Climate Change assessed an average Earth energy imbalance of 0.79 W/m² for 2006–2018, with an assessed range of 0.52–1.06 W/m². This is a period-specific estimate, not a fixed planetary constant. Changes in radiative forcing and climate feedbacks alter the balance as the system evolves. (ipcc.ch)
The ocean stored approximately 91% of the energy gained by the Earth system during 1971–2018. The remainder warmed land and the atmosphere or contributed to ice melting. Ocean heat storage is therefore central to interpreting planetary imbalance: surface air temperature alone does not measure the total accumulated energy. Ocean warming also contributes to sea level rise through thermal expansion. (ipcc.ch)
Observation and uncertainty
Satellite radiometers, particularly Clouds and the Earth’s Radiant Energy System instruments, measure reflected solar and emitted thermal radiation. Their observations are combined with imagery describing clouds, atmospheric particles, and surface conditions to derive radiative fluxes. Geostationary observations help fill gaps between satellite overpasses and represent variations through the day. (ceres.larc.nasa.gov)
Independent estimates use changes in ocean heat content and other energy reservoirs; the Argo program provides extensive ocean-temperature observations. Combining satellite and heat-storage evidence is important because the net imbalance is small compared with the incoming and outgoing fluxes. Calibration, sampling, and incomplete coverage introduce uncertainties. Energy-budget observations also test climate models and constrain their representation of radiation, clouds, and energy transport. (ipcc.ch)