First, I’d like to comment on your statement that, “The issue of whether clouds can cause El Nino is a red herring.” I agree, and I assume from this that you also have no physical evidence that clouds are causing surface temperature changes. If you did, you would be advancing it as a fatal flaw in my paper.
What’s puzzling is that I just re-read the comment you submitted to Science about my paper. In it, your first and main point is: “These results imply that [Dessler’s results are] ... not indicative of the cloud feedback, but is largely a consequence of the temperature changes induced by non-feedback cloud variations.” That sure sounds like “clouds cause ENSO” to me.
So have you concluded that your comment to Science is now a “red herring”? Are you going to withdraw it?
OK, now on to the meat of your e-mail. You make the argument that there are certain time scales over which the feedback must be calculated.
To be honest, I simply don’t follow the logic of your argument. Luckily, it sounds like this is really point number 2 from your Science comment, which is reasonably clear: “A second problem arises from the use of regression over the whole record. The problem here stems from the fact that feedbacks introduce temporary imbalances to the radiative budget (over time scales of hours to months), but over longer periods (years to decades depending on climate sensitivity), the system equilibrates so as to eliminate these imbalances (6). Using the whole record acts to distort the feedback estimates by including equilibration as well as feedback. More accurate estimation of feedback requires the isolation of the specific feedback signals (5, 6).”
I have two responses. First, as I wrote in my response to the Science comment, “Their second criticism indicates confusion between forcing and feedbacks. It is forcing (e.g., an increase in greenhouse gases, a brightening Sun) that generates imbalances in the Earth’s radiative budget. This radiative imbalance then causes the planet to warm, restoring equilibrium. Feedbacks do not create a radiative imbalance — they simply change the magnitude of the warming necessary to restore radiative balance. When estimating the magnitude of a feedback, there is no requirement that the Earth’s surface temperature be either in or not in equilibrium.” Clearly, as articulated in your Science comment, this argument is fundamentally wrong.
Second, I wonder what the source is of the claim that we must consider equilibrium time scales in our analyses of feedbacks. It appears to be reference 6, which is Lindzen and Choi 2009. But the claim is not proven in that paper --- it is simply assumed (in paragraph 5 of that paper). Can you provide a reference where some evidence is presented in support of this claim?
Thanks!
posted by Andrew Dessler at 2:47 PM on Jan 17, 2011
"Dessler e-mail to Lindzen on 1/17/11"
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