Global Warming
Climatology and Climate Changes
Air Pollution

What is a runaway greenhouse effect?

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2011-07-12 10:29:22

A runaway greenhouse effect (sometimes called an

abrupt greenhouse effect) happened on Venus, where

positive feedbacks caused the atmosphere to grow warmer and

warmer until the oceans boiled away. All the oceans boiled into

steam in the atmosphere and the water vapor (H2O) broke into

hydrogen (H) and oxygen O2). The hydrogen escaped into space and

the oxygen recombined, usually forming carbon dioxide. Venus'

atmosphere is now 96% carbon dioxide and the temperature at its

surface is 467°C (872°F).

A positive feedback occurs on earth with the ice caps.

White ice caps reflect the sun's heat, so the earth stays a bit

cooler. This is called the albedo effect. But if other things

happen and the ice melts, then the land underneath is dark and does

NOT reflect the sun's heat. Instead it absorbs it,

and the earth gets hotter. (The earth getting hotter makes the

earth get hotter still!)

Another positive feedback on earth is the frozen tundra.

As the earth warms, the frozen tundra thaws. As the tundra thaws it

releases methane gas, a powerful greenhouse gas. The methane gas

adds to the greenhouse gases and makes the earth warmer. (The earth

getting hotter releases methane making the earth hotter still!)

Earth does not have a runaway greenhouse effect. Earth

has an enhanced, or accelerated greenhouse effect, but scientists

are fairly confident that our positive feedbacks will never be

strong enough to cause a runaway greenhouse effect.


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