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 Global
Outgoing Longwave Heat Radiation
The orange-red areas of this image show
heat being emitted from relatively cloud-free bands north
and south of the equator. On the other hand, the dark blue
areas over Amazonia, North America, tropical Africa, Indonesia,
and Asia show where less heat is being emitted—in these
areas, the earth’s heat is being trapped by thick, high
clouds. Clouds tend to form over warm areas (like tropical
landmasses) as heat rises. The heated air cools as it rises,
and the water vapor it contains condenses to form clouds.
NASA’s Terra satellite system measures the infrared radiation
emitted by the earth, showing where the atmosphere allows
heat to escape back into space. This picture offers a way
of seeing the greenhouse effect in action. The amounts of
greenhouse gases in the atmosphere partly determine the strength
of the atmosphere’s ability to keep the planet warm:
Increases in global carbon dioxide concentrations, for example,
trap more heat near the planet’s surface.
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