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Topic: Climate Change  (Read 4756 times)

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Offline adkinsjr

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Climate Change
« on: December 06, 2009, 10:55:19 PM »
I have a question about the debate on climate change. It seems that people often claim that CO2 doesn't contribute to temperature. I understand that the earths climate is a complex system, with many variables effecting temperature. I understand that correlations do not conclusively prove causation. Obviously the earth could cool while CO2 increases if some other variable is at play.

What puzzles me is that the physics of it seem pretty straight forward. The vapor, methane, and carbon dioxide in the atmosphere absorb radiation causing them to vibrate. This means heat right? So more carbon could cause more heat? Why do some people claim that carbon doesn't alter the temperature? What am I missing?

Offline Borek

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Re: Climate Change
« Reply #1 on: December 07, 2009, 03:22:01 AM »
The physics is not as obvious as you suggest. Absorbed energy is also almost instantly reemitted, so some claim that greenhouse gases are in fact transparent. That's not exactly true - while absorption and emission are fast, emission occurs in the random direction, slowing energy transport, as half is effectively reflected back. But details are fine and difficult to estimate.

Better place for this question would be physicsforums.com - search before asking, as there were several long threads on the subject in the last years (check Other sciences/Earth subforum).
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Offline doc30

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Re: Climate Change
« Reply #2 on: December 07, 2009, 09:35:11 AM »
Most CO2 IR absorbing bands are already 100% absorbing in our atmosphere. It's the hot bands of CO2 that are invovled in the greenhouse effect. These are weakly absorbing rotational modes down around 667 cm-1, which roughly overlaps the black body radiation maximum for the surface of the Earth in our temperature range. These bands increase in absorbance with T (that's why they are called Hot Bands). The calculations for temperature increase are accurate to 5 decimal places under our atmospheric conditions.

Brief overview is here:

Even though the physics of heat retention by CO2 is a very well understood process. The effect on climate is the diffucult problem because there are so many feedback mechanisms that are fairly close so the effect on climate of a slight temperature increase is very, very difficult to predict.

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