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The radiation balance of the atmosphere is depicted in the diagram above. (Shortwave solar radiation is colored purple and longwave radiation is in red.) Fifty-one percent of the energy available at the top of the atmosphere is absorbed by the surface as direct or indirect solar radiation. The gases of the atmosphere are relatively poor absorbers of solar radiation, taking in only 19% of what is available. Over a quarter of the available solar radiation is reflected or scattered back to space before it reaches the ground. That energy that is absorbed by the surface is re-radiated by the earth as longwave radiation. The gases that comprise the atmosphere are relatively good absorbers of longwave radiation, keeping the lower atmosphere fit for life to flourish. This radiation is emitted downward toward the surface as longwave atmospheric counter-radiation keeping near surfaces temperatures warmer than they would be without this blanket of gases. This is known as the "greenhouse effect". However, amount of outgoing longwave radiation balances that which is gained by the earth. |
