Global Energy Flows

Global Energy Flows

Global Energy Flows (W/m2)

Solar energy drives the Earth's climate system. Based on measurements from satellites and other instruments, we can trace the flow of energy through the climate system. Note that the numbers are best estimates in Watts per square meter as of 2009. We can expect these numbers to change as our observations and understanding improve.

Energy comes into the climate system as shortwave solar radiation. Some of that energy reflects off clouds and the atmosphere back to space. Some more is absorbed by the atmosphere.

The rest makes its way to the surface, where most is absorbed but some is also reflected. The difference between the incoming and the reflected energy is the total available to the Earth's climate system. About two-thirds of that is absorbed by the surface, while the rest is absorbed by the atmosphere.

Solar energy absorbed at the surface warms the surface, which radiates thermal, or longwave, radiation.

Some of that radiation makes it directly out to space through the so-called atmospheric window and some more is absorbed by clouds. There are also greenhouse gases in the atmosphere, particularly water vapor and carbon dioxide, that very efficiently absorb longwave radiation and radiate it.

Greenhouse gases radiate in all directions so that some radiated energy is directed upward toward space, with the remainder directed downward toward the surface.

Radiative transfer isn't the only way that energy moves between the surface and the atmosphere. The surface also loses energy through evapotranspiration from plants and wet surfaces (latent heat), and through conduction (sensible heat).

Climate models need to account for all the processes that modulate this flow of energy. For example, clouds reflect, absorb, and radiate energy. Therefore, the cloud processes need to be accurately simulated in climate models. Similarly, vegetation strongly modulates energy flow by affecting albedo and evapotranspiration.