Sunday, January 31, 2010

Carbon dioxide feedback.

The recent paper in Nature of Frank et al on CO2 feedback has had a run in the blogosphere. That was started by a review in Science Daily. Briefly, the paper says that the minor feedback mechanism by which warming causes CO2 to be expelled from the oceans, causing more warming, is less than some recent estimates. The key figure is the increase of CO2 in ppmv resulting from 1C warming, and Frank et al give a median figure of 7.7, with a range from 1.7 to 21.4.

That's actually a pretty wide range. But does it refute any sort of consensus? I looked up what the AR4 had to say. There wasn't much, but in Chap 7, sec 7.3.4.3, I found this:
“A 1°C increase in sea surface temperature produces an increase in pCO2 of 6.9 to 10.2 ppm after 100 to 1,000 years (Heinze et al., 2003; see also Broecker and Peng, 1986; Plattner et al., 2001). “

That seems quite within the range Frank et al find. Yet people who suggest some pillar of AGW has fallen say that recent estimates were up to 40 ppmv/C. Lubos Motl had cited that figure, so I put the IPCC figure to him. He cited this 2006 paper by Scheffer, Brovkin and Cox as the source of the 40 ppmv/C claim.

I looked up that paper. They had deduced their estimate from the CO2 response to the LIA, and said
we arrive at an estimated carbon sensitivity (α) to temperature of 41 (following  Mann and Jones) to 12 (following Moberg et al) ppmv CO2°C.


A rather ambivalent figure to be refuting.
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2 comments:

  1. carrot eaterJanuary 31, 2010 at 10:29 AM

    My hunch is that this value is different under different conditions - that 1 C of warming at the coldest part of an ice age will have a different effect from 1 C of warming in the interglacial.

    I think what we're seeing here is a conditioned response. They see some article somewhere that says 'less than thought', and they run with it without checking what was actually thought. We saw the same thing with the airborne fraction paper of Knorr, though I think many simply misunderstood what that paper was saying.

    By the way, if a certain blogger tries to make some hay out of this paper, and they then tomorrow try to suggest that the current rise in atmospheric CO2 concentrations is due to release from the oceans and not combustion/cement, would somebody please, please call them out for being totally inconsistent?

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  2. Nick StokesJanuary 31, 2010 at 11:15 AM

    Yes, on looking at that AR4 figure, I had a feeling of having heard the other side argued - the rise in CO2 is natural and came out of the sea in response to the MWP.

    Yes, it us slightly different - I think Frank means GMST and AR4 has SST. But they are related.

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