Melting in Greenland

Via desmogblog, a Nasa article about snow melting in Greenland: NASA Finds Greenland Snow Melting Hit Record High in High Places. A new NASA-supported study reports that 2007 marked an overall rise in the melting trend over the entire Greenland ice sheet and, remarkably, melting in high-altitude areas was greater than ever at 150 percent more than average. In fact, the amount of snow that has melted this year over Greenland could cover the surface size of the U.S. more than twice.

But look more closely: the graph shows, and the text says, that 2007 has less melt than several other years. There is clearly a nice upward trend, but 2007 (despite the low sea ice) doesn't look like a record. I think what they have done is looked at the area above 2000m and found a record max for that, not the whole sheet.

[Update: several people have noticed that the area comparison against the US is misleading at best and more resaonably described as "horse.. er.. hogwash". They add up the daily snowmelt area to get their total; they could as reasonably add up the hourly or secondly area to inflate their numbers more (OK, so its a daily product, so that isn't quite true; but their "area" isn't comparable to the US) -W]

More like this

"the amount of snow that has melted this year over Greenland could cover the surface size of the U.S. more than twice."

To what depth?

[When they say "amount" they mean area. Thats (nearly) all the satellite knows -W]

Thanks William - I see what they've done; they calculate the melting area each day, accumulate it over the year and compare the total to the land area of the US. Which strikes me as rather odd, but I suppose it conveys an impression of scale.

[Yes, you're right, I hadn't realised that. Which makes the comparisons to US area highly misleading -W]

Emergency call for Dr. Tufte! Paging Dr. Tufte!

"In fact, the amount of snow that has melted this year over Greenland could cover the surface size of the U.S. more than twice."

Since Greenland is much smaller than the US, what could this possibly mean?

It is misleading nonsense. Look carefully at the graph which they imply is in units of US-area (or lower-48 area?) The horizontal axis is in km^2-day but the vertical axis is in years. I'm fairly sure that there is a factor of 365 hiding here; the square-km-days are added up over the 365 days of the year. The denominator needed to make this a reasonable measure of area is missing.

Using the bogus measure that I think they use, ice "covers" twenty times the area of the US in a decade, but "covers" less than one per cent of the US in a day.

The trend is real enough, but the area comparison is complete horse.. er.. hogwash.

Odd tidbit in the latest EOS (weekly 'newspaper' from the AGU) in a small article about a conference on karst geology --- mention that it has always been assumed that karst formation stops under glaciers, but now there is some reason to believe that it accelerates instead and that this will change what we think about the timing and age of karst areas. (Latest issue of last week but it seems our recycling's taken it away already, no cite, sorry.)

Any limestone under the currently interesting icecaps?

I'd guess this is part of the discovery of active moving water under the ice, and open channels --- which I gather is all relatively new thinking.

Weren't polar icecaps and continental glaciers thought to be frozen and on cold rock, til recently?

By Hank Roberts (not verified) on 01 Oct 2007 #permalink

Just hints. (Note the terminolgy distinction between 'glacial karst' or ice melt caves in the glacier, vs. limestone karst interacting with overlying glaciers)

Glacial karst as possible reason of quick degradation of Scandinavian glacier sheet
BR Mavlyudov - Glacier caves and glacial karst in high mountains and polar ..., 2005 (Google Scholar, just a note that it was cited by another paper)

Fascinating hints about Antarctica, here:
Glacial caving in antarctica | La Venta Exploring Team

"....the classical glacier karst phenomena are very small. Nevertheless, unexpected speleo-genetic phenomena create caves in other parts of the continent, at temperatures far below zero, where the "thermokarst" definition appears inaccurate.

"We emphasize that these studies are absolutely just beginning, but we may give here a general idea of what we know about caves formation in Antarctica. ...."
"2) Volcanic glacier karst, that is ice caves formation as a result of volcanic heat release (fumaroles). These caves are subglacial, dug on the contact of ice with rock. It is a cave type well known in Iceland, but in that case the water released by melting flows away due to "high" ice temperature. The cases seen in Antarctica up to now (on Mt Erebus and Mt Melbourne) show caves formed in ice at 30-40 degrees below zero, where the water cannot at all flow away. The water transfer (and the digging) is entirely made by the vapour phase, thanks to strong draught in the caves. At the entrance the out flowing vapour sublimates and forms typical well heads.
"3) Marine glacier karst, that is caves formed on the contact of glaciers flowing from the Plateau and the sea. The entrances of these caves are in the front of glaciers floating on the sea, and are probably created by the temperature difference between the glacier ice (-20°C) and the fast ice (sea ice, at -2°). Probably, in the semi-closed system of glacier fractures the fast ice sublimates and deposits energy and crystals on the cold roof, hollowing it out and widening the cave up to very large structures (thousands of cubic meters). The internal draughts and the marine salt surely play a role, but many further studies are necessary to understand the phenomenology of these unexpected caves."
"... some limestone deposits have been described; studying their tracks of ancient karst phenomena would surely be interesting, but they are so far from the bases that such research really appears to be very difficult to carry out."

PhD candidates, there's a potential for a relatively warm and friendly Antarctic research environment available for you, if you can get there before the survivalists and oil explorers take them over as bases.

By Hank Roberts (not verified) on 01 Oct 2007 #permalink