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Bart Verheggen says:
Anthony,
Could you please point out where in this paper it is mentioned that “clouds have large negative-*feedback* cooling effect on Earth’s radiation budget”?
I may be wrong, but I think you’re confusing two issues:
- the net effect of clouds on climate
- the net feedback of clouds on a change in climate
The paper, as I read it with a first quick overview, addresses the first, whereas you interpret it as if it addresses the second.
They are two distinctly different issues. The second (clouds as feedback) is about how cloud cover and properties might change in response to a warming or cooling of the climate: Will the net cloud radiative effect become more or less negative.
The net radiative effect of clouds on climate has long been known to be negative (i.e. cooling). See e.g this quote from the paper: “The overall global net cloud radiative effect is one
of cooling as documented previously (Ramanathan et al., 1989).” That can be verified in any textbook on the subject and most introductions of papers on this topic.
See also http://ourchangingclimate.wordpress.com/2009/04/16/aerosols-clouds-and-climate/
REPLY: Thanks, I can see where you’re coming from, but I saw things differently. See the update I posted at the end of the article. – Anthony
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Roy W. Spencer says:
Bart is correct. This paper is not about cloud feedback…it is about the average effect of clouds on the climate system, which the IPCC, Trenberth, Dessler, et al. will all agree is a cooling effect. It is an update of the early estimates from ERBE many years ago.
Feedback is instead how clouds will change in response to a temperature *change* from the average climate state.
Now, it might well be that since the average effect of clouds on the climate system in response to radiative heating by the sun is to cool the Earth, then a small increment in radiative heating (e.g. from more CO2) will ALSO result in clouds having a further increment in cooling. That’s basically what Monckton has been claiming, and he might well be correct. Lindzen pointed this out also in his 1990 BAMS paper.
I just wanted to point out that the IPCC view is that this paper is not about cloud feedback….even though it might be about cloud feedback. ;)
REPLY: Thanks Roy for the clarification. The question of whether clouds act as feedback, forcing, or both is one that will occupy us as a while. My interpretation is as both, they act as a forcing (albedo) and as a feedback via the water vapor cycle, see Willis: Further Evidence for my Thunderstorm Thermostat Hypothesis
See the update I’ve posted.
– Anthony