Amplifiers: Water Vapor
Today, water vapor produces two-thirds of the world’s greenhouse effect. All of the other gases – carbon dioxide, methane, nitrous oxide, halocarbons, etc. – contribute the other third. The effect of water vapor is so significant that the global average temperature would be below freezing without it.
Warm air can contain more moisture than cold air. This is the basis of the water vapor feedback. As the atmospheric temperature rises and the amount of water vapor increases, the greenhouse effect is enhanced, further increasing temperature.
The water vapor feedback is critical for producing the glacial/interglacial cycles. Uncertainty in the magnitude of the water vapor feedback is an important source of uncertainty in projecting future climate warming.
A Common Source of Confusion
Does the water vapor added to the atmosphere by cooling towers and smokestacks contribute to global warming?
These sources are tiny compared to natural evaporation from the land and ocean. However, the water vapor feedback is important in increasing water vapor concentration and the greenhouse effect.
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