Dessler e-mail to Lindzen on 1/17/11

Dick-

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!