Interactions between the atmosphere, hydrosphere, biosphere, and lithosphere control global climate. Global climate represents a balance between the amount of solar radiation received and the amount of this energy retained in a given area. The planet receives about 2.4 times as much heat in the equatorial regions as in the polar regions. The atmosphere and oceans respond to this unequal heating by setting up currents and circulation systems that redistribute the heat more equally. These circulation patterns are in turn affected by the ever-changing pattern of the distribution of continents, oceans, and mountain ranges.
The amounts and types of gases in the atmosphere can modify the amount of incoming solar radiation, and hence global temperature. For instance, cloud cover can cause much of the incoming solar radiation to be reflected to space before being trapped by the lower atmosphere. on the other hand, greenhouse gases allow incoming short-wavelength solar radiation to enter the atmosphere, but trap this radiation when it tries to escape in its longer-wavelength reflected form. This causes a buildup of heat in the atmosphere and can lead to a phenomenon known as the greenhouse effect.
The amount of heat trapped in the atmosphere by greenhouse gases has varied greatly over Earth's history. one of the most important greenhouse gases
Plot showing how the average temperature on the surface of the Earth has changed with time over the past several hundreds of millions of years. These represent slow, long-term changes in global temperature.
Millions of Years Ago (Ma) 290 210 145
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