On 18/02/2008, Hank Roberts <[EMAIL PROTECTED]> wrote:
>
>
>
> On Feb 16, 4:04 pm, James Annan <[EMAIL PROTECTED]> wrote:
> ...
> > I suppose I should submit it to Nature :-) ...
>
> How much attention does it warrant? How much attention is it getting
> from the people funding your modeling work? Anyone take these runs
> seriously, or are they the handful in hundreds?
Not much, not much, no-one, and handful in about 100 :-)
I take it as a salutory reminder of the limitation of this class of
model (experiment). You may not realise, but in these experiments the
atmosphere is "tied" to a sea surface which is forced to have
realistic temperatures and which (crucially) acts as an infinite
source or sink of heat (and freshwater, although this may not matter
so much). So the actual radiative behaviour of the atmosphere may not
be at all realistic when we push parameters to extreme values.
Furthermore, we can only evaluate the model by looking at equilibrium
situations (eg pre-industrial climate) and not explore the transient
response in any quantitative sense, since the model lacks the thermal
inertia of a deep ocean.
The only time I saw someone try a hindcast of the last 100 years with
a model that had a sensitivity of ~10C, it was completely crazy. High
sensitivity means low stabilising radiative feedback so the
temperature oscillated rather wildly, especially in response to
historical volcanic eruptions. In principle one might be able to get
such a model to work passably by adjusting other uncertainties such as
deep ocean heat uptake, but the amount of evidence you have to
handwave away in order to defend this makes the whole process a bit
fantastical...which is why I say that sensitivity is very likely close
to 3C, although it is not possible to formally *prove" that much
higher values are impossible.
James
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