Posted on 03/16/2004 2:20:53 PM PST by cogitator
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."
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.
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