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Дата изменения: Fri Jun 8 23:31:38 2007
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All kinds of death - 5

Sustaining civilisation - 4

lecture15 D 4 --- | --- D 6 Next

The greenhouse effect and overheating



Energy balance in a planetary atmosphere

The earth is heated by solar radiation; a fraction of the energy absorbed is re-radiated. The temperature within Earth's biosphere depends on the balance between energy absorbed and re-radiated.
Certain gases (carbon dioxide, methane) are very efficient at trapping the re-radiated flux



A major methane source



Hurricane Georges, Sept, 1998

More energy leads to higher temperatures - many possible
greater possibility for violent storms (powered by heat)
higher water levels as reduce level of polar ice caps.
Current satellite data suggest a warming trend of ~0.05 degrees Centigrade / decade

A runaway greenhouse effect can raise temperatures substantially
T > 100 C, water boils, the oceans disappear - adds more CO2 to the atmosphere
becomes even more efficient at trapping heat
Consider Venus - atmosphere dominated by carbon dioxide
"natural" temperature is ~30 C; actual surface temperature, 500 C



Venus - an extreme case of the greenhouse effect