Antarctica


This peculiar figure is still up at a NASA site. The cooling rates are monstrously high (per annum!) and the boundary between land and sea is too sharp and there is altogether a misleading amount of detail. I seem to recall William Connolley warning me that this map was broken. But there it sits.

Meanwhile Robert Rohde’s wonderful GlobalWarmingArt site finds the evidence equivocal:

Here the rates are per decade, and while still large, are not stunningly large. The time series are longer and hence perhaps less noisy, and the trends are far less uniform. (And as usual, Robert has made a visually beautiful image. Quite a few of those many hits to this site have been people coming by to admire my closeup of one of his sea level rise maps.)

Anyway, the NASA site with the peculiarly shaded map has a link to:

Comiso, J. C., Variability and trends in the Antarctic surface temperatures from in situ and satellite infrared measurements, J. Climate, 13(10), 1674-1696, 2000; Kwok, R, and J.C. Comiso, Spatial patterns of variability in Antarctic surface temperature: Connections to the Southern Hemisphere Annular Mode and the Southern Oscillation, Geophys. Res. Lett., 29(14), 10.1029/2002GL015415, 2002;

And therein we find this:

Although the NASA web page references the article, and while it has some obvious features in common, this figure doesn’t perfectly match their fancy shaded map (check the area by the Ross Sea). That said it does show relatively steep gradients at the shore, and very high rates of change. Notice that the warming signal in the surrounding seas is far more pronounced than the cooling in the interior. Notice especially the intense warming near the Amundsen embayment, (a bit west of South America) which is spectacularly not where you want it.

So what’s going on?

Wikipedia (and thereby, William, no doubt) refers us to

Thompson and Solomon 2002, Interpretation of Recent Southern Hemisphere Climate Change, Science, v 296 pp 895 ff.

They in turn make a strong case for a correlation of cold Antarctic interiors and a tightening of the “SAM”, which is the anomalously strong phase of the Antarctic polar vortex, a mode which appears to be increasing, and which can be dynamically attributed to a sharp decline in ozone over the period record. Ozone, of course, heats the stratosphere, so its decline will lead to anomalously cold temperatures. Then you need to invoke the thermal wind law and (hmm skipping a few steps) voila! a tightened Antarctic vortex, and tightened temperature gradients around the Antarctic rim.

Of course for every person worried about the retreat of Arctic sea ice there is somebody willing to celebrate the advance of Antarctic ice. The map shows that ice is advancing through the relatively limited areas of cooler water, but that doesn’t do much to separate cause and effect. Any ideas out there?

Anyway the short version of the story is at least plausibly argued to be like this. Antarctica seems to be special because of ANOTHER human impact on the global environment. As the ozone depletion subsides, this will be tested, as the anticipated forcings will both be towards warming in the Antarctic interior.

Update: I see Atmoz has taken this on in plenty of detail. The info I wanted from William is there too, along with many comments. And he says the shiny map is “probably the work of a PR droid” and points to this, via NASA, from Wikipedia:

Go figure.

I think there is actually something to complain about here in a McIntyrean way: how are these drastically different results from a single agency supposed to be reconciled? I note that the web publication of the later image refers to the earlier one without explaining the dramatic differences.

And while I haven;t heard a cogent explanation for the advancing Antarctic sea ice, I have heard a cogent explanation for interior cooling, along with, now, data that shows it isn’t happening…

None of which changes the fact that so far all evidence seems to agree that warm water is being delivered to the structural weak point of the West Antarctic Ice Sheet.