William M Connolley wrote:
> On Wed, 27 Sep 2006, [EMAIL PROTECTED] wrote:
> > > This is a weird thing to say. The 2001 report had Ant and Gr just about
> > > cancelling out. That wasn't at all implausible, it was what the science
> > > says.
> > > Fairly recently has come some evidence for more melt. Is (10) a ref to
> > > 2001 or
> > > 2007?
> >
> > It's 2001.
>
> Then Hansens comment is very odd.
Hansen's position is clear enough, and doesn't strike me as odd. His
last few papers have included (or focussed on) concerns about ice-sheet
stability (melting being a wet process, with positive feedbacks), and
the comment discussed above leads on to this:
"In assessing the level of global warming that constitutes DAI, we
must bear in mind that estimated climate sensitivity of 3 +/- 1°C for
doubled CO2, based mainly on paleoclimate data but consistent
with models, refers to a case in which sea ice, snow, water vapor, and
clouds are included as feedbacks, but ice sheet area, vegetation
cover, and non-H2O GHGs are treated as forcings or fixed boundary
conditions. On long time scales, and as the present global
warming increases, these latter quantities can change and thus they
need to be included as feedbacks. Indeed, climate becomes very
sensitive on the ice-age time scale, as feedbacks, specifically ice
sheet area and GHGs, account for practically the entire global
temperature change (17)."
The paper is also (of course) careful to distinguish between
equilibrium and transient responses, although Hansen considers both of
those to be faster than some might like.
Re: El Ninos. The paper suggests that there could be an increase in
intensity of El Ninos, but not necessarily an increase in frequency. If
I'm reading it right, increasing SSTs combine with still-cool upwelling
deep water to intensify the pattern. What happens when the deep water
warms is, of course, an open question, but we won't have any ice sheets
by then...
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