cc: Martin Manning date: Wed, 6 Sep 2006 09:32:56 -0400 from: David Rind subject: Re: [Wg1-ar4-ch06] urgent IPCC need to: Fortunat Joos , Jonathan Overpeck , WGI-chap6-ar4 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? _______________________________________________ Wg1-ar4-ch06 mailing list Wg1-ar4-ch06@joss.ucar.edu http://lists.joss.ucar.edu/mailman/listinfo/wg1-ar4-ch06