Thursday, March 22, 2012

2727.txt

cc: Martin Manning <mmanningatXYZxyznoaa.gov>
date: Wed, 6 Sep 2006 09:32:56 -0400
from: David Rind <drindatXYZxyzs.nasa.gov>
subject: Re: [Wg1-ar4-ch06] urgent IPCC need
to: Fortunat Joos <joosatXYZxyzmate.unibe.ch>, Jonathan Overpeck <jtoatXYZxyzrizona.edu>, WGI-chap6-ar4 <wg1-ar4-ch06atXYZxyzs.ucar.edu>

Hi,

I hope this isn't nitpicking, but using the words 'very likely' in
combinaion with the reset of the sentence gives a statistical
meaning, from the IPCC perspective, that says very strongly that ALL
of those things contributed to the positive amplification. Some of
them one would think very likely did: changes in greenhouse gas
concentration, ice sheet and sea ice changes, and most likely
biophysical feedbacks - but we really have no idea whether ocean
circulation changes were a positive or negative feedback (and
different modeling groups have gotten opposite results in this
regard). The circulation changes implied by the CLIMAP SST
reconstruction (reduced poleward heat transport) actually was a
negative feedback in our modeling results by keeping the tropics warm
and minimizing the water vapor reduction. In coupled models, one set
of studies showed that decreased deep water formation was necessary
for the positive feedback, while another set showed increased
circulation was the trigger. Even dust is an issue - over a vegetated
surface, or the ocean, it is clearly a positive amplification, but as
Jonathan knows well, modeling studies suggest it is a negative
feedback over snow and ice surfaces. Some studies have it helping to
force the peak of an ice age, while in another it is a prime
component in ending it. So I would suggest the following, somewhat
less definitive version:

* The widely accepted orbital theory suggests that
glacial-interglacial cycles occurred in response to orbital forcing.
The large response of the climate system implies the necessity for a
strong positive amplification of this forcing. Changes in greenhouse
gas concentrations, ice sheet growth and decay, ocean circulation and
sea ice changes, biophysical feedbacks, and aerosol (dust) loading
are among the responses that influenced climate sensitivity.

David

At 12:57 PM +0200 9/6/06, Fortunat Joos wrote:
>* The widely accepted orbital theory suggests that
>glacial-interglacial cycles occurred in response to orbital forcing.
>The large response of the climate system implies a strong positive
>amplification of this forcing. Changes in greenhouse gas
>concentrations, ice sheet growth and decay, ocean circulation and
>sea ice changes, biophysical feedbacks, and aerosol (dust) loading
>have very like contributed to this amplification.
>
>Not sure David is happy with it?
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