2005-08-02

Polar amplification and MSU, combined.

A little while ago I write about the mechanisms of polar amplification of warming: which appear to be mostly ice-albedo feedback and the dynamical habit of the tropics of exporting information. The old favourite - inc GHG can have more effect when its cold - didn't seem to figure.

But now, idly googling for "Spencer and Christy" I came across S+C's report for 1978-2003. It will probably all have to be revised when the vn5.2 data finally becomes "official", but therein they offer this:

That cold air has very little water vapor in it, so if you add another greenhouse gas you have an opportunity to trap more heat. When you go to the tropics, where there’s lots of water vapor, the extra carbon dioxide doesn’t have as much effect. As a greenhouse gas, carbon dioxide’s greatest effect is in the driest, coldest places


I rather suspect this is wurble, with no analysis behind it: its an explanation in search of an effect. But its its interesting to see someone who (presumably) knows something about atmospheric radiation putting it forward. By contrast, Keith Shine (who very definitely does know about radiation) didn't recognise the idea (pers. comm.).

Another interesting feature of that report is that the second major headline of it is "The atmosphere is warming" in big letters. Oddly enough, the std.spetics don't seem to have picked up on that... in fact, I sometimes wonder if S+C have noticed, either...

5 Comments:

Anonymous Steve Bloom said...

William, I don't know if you ever look at Pielke Sr.'s new blog, but a small controversy has come up regarding Arctic sea ice trends: http://ccc.atmos.colostate.edu/blog/?p=7#comments. Any thoughts?

8:21 pm  
Blogger Belette said...

Its not on my list (John...?) but I've made a comment (hey that cost me an hour out of this evening...).

It looks to me like RP(Sr) is wrong on the summer trends. will be interesting to see how he responds.

9:45 pm  
Blogger Belette said...

Curious... I can't get my comment to show up here. Let me post it in here:

----

Hmm, I find this looking at individual months of individual years a bit odd. Its not going to tell you much.

Unless I’ve made some mistake, the long-term trend for summer (sept) ice is indeed steeply downwards (here) . The trend looks like 9%/decade, which is entirely consistent with the ACIA report. See here for the area trends (/decade). For the annual mean I get about 3-4%/decade (all this from Bootstrap data, of course). I dont see how your conclusion can be sustained.

I would certainly criticise the ACIA report (or anyone else) who tried to merge the 1973-1978 data into the SSM/R series though: pretty well everyone agrees you can’t do this well. And I can’t see where the “recent acceleration” comes from.

I guess they didn’t cite your paper because it did that weird stuff with insolation weighting.

And re comment 1: the point is, the ice sheet responds to many things, including long-term changes in its level unconnected to (this years) snowfall.

Comment by William Connolley — August 2, 2005 @ 3:42 pm

11:08 pm  
Anonymous Anonymous said...

It is not such a stupid idea. Given the lapse rate you don't have to get very high before the water vapor concentration is less than that of CO2. I suspect that the major effect though is setting the effective TOA height. Being Saturday, being lazy, I will leave it with the old wave of the hand.

Eli Rabett

3:48 am  
Anonymous Alastair B. McDonald said...

As the anonymous Eli Rabett said it makes sense to argue that adding CO2 to the atmosphere will have more effect at the poles where there is little or no water vapour. It certainly fits with what Alexeev et al. found. See
http://www.springerlink.com/app/home/contribution.asp?wasp=73d2f377b47446c18cb10b91f8cbd5e6&referrer=parent&backto=issue,1,7;journal,2,125;linkingpublicationresults,1:100405,1

Cheers, Alastair.

5:05 pm  

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