Global Climate: Study Confirms (and Reduces Potential Impact of) Water Vapor Feedback Process

Science Daily ^ | March 16, 2004

[ancient_geezer]

Where did you see those values?

I find very interesting that one of the major criticisms leveled at GCMs is that they overestimate the warming signal substantially. The authors of this piece may have hit on one of the primary reasons for that.

Sorry I was unable to get right back. The big boss had other ideas like taking her shopping ;O/

Looks like I misread that particular section. The actual result of the author's check was the GCM (fixed relative humidity assumptions) produced a 30% greater surface warming of 1.6 K over the author's unconstrained model. 1.6 = T/(1+.30)

That works out to be 77% of 1.6K = 1.23 K.

For the lower measurement values (h=1/20 as opposed to 1/10 relative humidity), that would be approx 59% of 1.6K, ~0.95K assuming the temp to humidity function to be approximated by the limiting relation 1.6K = e^-kh.

http://www.atmos.umd.edu/~dessler/UTHfeedback.pdf

Section 3. Results, page 7:

"On the other hand, maintaining a constant model profile of relative humidity produces larger UT mixing ratio increases, on the order of 60-70% for doubled CO2. The stronger water vapor feedback leads to a larger surface warming of 1.6 K, which is 30% larger than calculated when relative humidity is not constrained to be constant."

[ancient_geezer]

Opps! should be

deltaT = 1.6K = e^-k/h

as the humidity factor(h) decreases, there is lower UT mixing, resulting in lower surface temperature change over unamplified CO2 response.

[Number_Cruncher]

Actually skeptics have been saying that the water vapor feedback has been overestimated by an order of magnitude and they have been saying it for more than 20 years.

How will the climate modelers respond? They won't change the models. They will attack this analysis of the data by doing their own analysis which will then re-interpret the data to make it agree with their model predictions. Nothing will change because of this paper.

The new results are consistent with a 0.08 C feedback warming due to water, using Modtran. The IPCC claims it is about 1.5 C, so this results erases half of the claimed warming.