Live (almost) from AGU–Dispatch #1

Welcome, dear readers. For all of you who have eagerly been awaiting Part II of Les Chevaliers, thank you for your patience; with all the other interesting stuff coming up for discussion at RealClimate, the plans to post Part II ran up against the American Geophysical Union Fall Meeting, when 15,000 of our prime audience are holed up in San Francisco trying to decide which of a half dozen simultaneous sessions at any time best command their attention. Be of good cheer — Part II will be coming along in about another week. Meanwhile, Yours Truly offers a few off the cuff dispatches giving a personal and unedited view of a few things going on at AGU that may be of interest to the RealClimate readership.Myself, I have been spending a lot of time looking at some of the exciting new data coming in from planetary missions, but I’ll spare you that, and talk about things related to global change. I do not pretend that these are necessarily the most important things going on at the meeting, but they are a few things that I happen to have attended, and which caught my attention.

Today, the climate change related session I got to was Climate Change in Greenland: Past and Present (session C13A), with M. Kelley, I. Hakansson and M. Nettles presiding. Actually, I only got to the second half, because of a conflict with a Mars climate poster session, but the half I got to was a real eye-opener. This was a well-attended (really packed, standing room only) session, that generated a lot of excitement. Perhaps I’ll be able to snag some of the images later in the meeting to show you, but meanwhile I’ll do my best to give you some of the picture in words at least.

To put things in perspective, I should first mention the talk by Tom Lowell, on work in collaboration with about a dozen other authors, concerning organic remains from the Istorvet Ice Cap in East Greenland. These are organic remains recently uncovered by the retreating glacier. Dating them tells you when the glacier had last retreated that far. Carbon-14 dates put the date of this earlier glacial retreat to between AD 800 and 1014, bracketing the time of the Norse colonization. Insofar as glaciers are primarily sensitive to temperature, that does indicate that in the Middle Ages this particular place, at least, was probably as warm as at present. It is an indication of some kind of regional warming in the area in the Middle Ages. Thus, if Greenland were taken in isolation, one couldn’t confidently say that what is going on there just now is completely unprecedented in the Holocene — at least not yet. However, as Tom would happily tell you, the Middle Ages were not as generally warm as the present, and Greenland shouldn’t be taken in isolation. It is the rapid melt in Greenland today, taken as one of a vast constellation of signatures of unusual warming, that gives one cause for concern.

And there was ample evidence presented of startling change going on in Greenland — changes in the ice that could raise sea level far beyond the projections given in the IPCC Fourth Assessment Report. J.E. Box and collaborators presented new work on Greenland outlet glacier sensitivity to surface melting. Outlet glaciers are the very dynamic “drains” through which Greenland loses much of its ice. Earlier work by Zwally et al documented the rapid sensitivity of surges in such glaciers to melt water forming on the surface and penetrating to the base. Box and company documented how ubiquitous the melt ponds are, and how every one, basically, is pouring water through a moulin down to the base. Valliant graduate students have waded chest-deep in the melt ponds to measure the rate of drainage. The work documented much more broadly than ever before how outlet glacier speed responds to warming of the environment.

Leigh Stearns and collaborators point out that the Greenland Ice Sheet’s contribution to sea level has doubled in the past five years, due largely to factors connected with ice dynamics (and not incorporated in the IPCC estimates). They showed satellite data which indicates that just two glaciers — Helheim and Kangerdlugssuaq — might account for 10% of this increase. Ominously, more glaciers are primed to pop as climate continues to warm. About the increased flow speeds in this region, they suggest the system has entered a new state: “We speculate that these faster flow speeds represent a new long-term state of behavior which, while not as dramatic as the short-lived periods of peak speeds, have important implications for the rate of sea level rise.”

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