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Q & A: water color and evaporation

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Most recent answer: 10/22/2007
Q:
Does the color of water effect the evaporation rate, and if so how does it effect the world?
- Simon (age 14)
Battle Creek Middle School, St. Paul, MN, U.S.A.
A:
We get a lot of canned questions about water color and evaporation, but yours has a useful twist. Obviously darker-colored water absorbs more light if it's exposed to sunlight and thus heats up more and evaporates faster. The biggest important difference is between liquid water in the oceans and frozen water, which reflects much more energy. As global warming sets in from our reckless emissions of CO2 and other greenhouse gases, there is less ice and more water, so more sunlight gets absorbed. Therefore more water evaporates. Water vapor itself is a greenhouse gas, so that amplifies the effect further. It's hard to calculate exactly how big this effect is, because it requires modeling how heat distributes in the oceans. That's one of the biggest uncertainties in estimates of how bad global warming will get. A combination of several positive feedback effects of this sort might lead to truly disastrous consequences, but right now the probability of more or less serious outcomes is hard to calculate.

Mike W.

(published on 10/22/2007)

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