Monthly Archives: January 2008

How not to discuss the Water Vapor feedback

I want to do a post soon on feedbacks, but just a quicky here

There is a lot of discussion about climate feedbacks in climate science, notably the role of water vapor. In short, the total amount of atmospheric water vapor should go up in a warmer climate under the assumption of approximately fixed relative humidity, at an increase of ~7% per degree Celsius warming, as per the Clausius-Clapeyron relationship. Water vapor is the strongest greenhouse gas, and so increases in water vapor will amplify any temperature changes from any initial forcing (e.g., CO2). However, many times the “water vapor feedback” being discussed on the internet is not the water vapor feedback at all. For example, in a recent web blog by Roger Pielke Sr., entitled Third Follow Up To Climate Metric Reality Check #3 – Evidence For A Lack Of Water Vapor Feedback On The Regional Scale or here, Dr. Pielke discusses how the WV feedback may not be showing up on the regional level and thereby questioning our understanding of how the climate reacts to temperature increase.

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