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logicman

Gas Glo: that's a very good question.

At the end of summer, when the water has warmed, the surface layers must cool enough for ice to form. Greenhouse gases slow down the rate of heat loss. As new ice forms, heat is released into the atmosphere and again its loss to space is delayed by greenhouse gases.

Warm water influx from the Atlantic doesn't depend on seasons.

As the water absorbs more heat, the delay between darkness and ice formation grows. The trend is that every spring sees thinner new ice. The newly formed winter ice has less thermal capacity than in former times, so it melts away sooner exposing the ocean to the sun sooner.

All of the factors work towards more melt in summer and less ice volume/mass recovery in winter. If/when there is an 'AHI' - Arctic Heat Island - a bubble of warm air over a pool of warm water, many of Greenland's glaciers will continue to calve well into winter and more melt pools will persist through winter than is currently the case.

It's all positive for ice loss.

Oslo

According to a letter to Nature in April 2010:

The evidence from the past two decades, based on ERA-Interim,
reveals that recent reductions in sea ice cover and thickness have been
great enough to enhance Arctic warming strongly during most of the
year.

http://sciences.blogs.liberation.fr/files/arctique-ann%C3%A9es-2000-tures.pdf

Evilreductionist.blogspot.com

Good melt today - provisionally 73,437. If we get average melt from here, we will be slightly above 5 million at the minimum.

Evilreductionist.blogspot.com

And when I say 'melt' I mean 'extent reduction'. ;)

Phil263

@ FrankD

You were right mate, we did get below the 2002 minimum on August 22 ( bar a significant upward revision tomorrow) !

Good prediction!

FrankD

Good prediction, Phil? Nope, just dumb luck - I facepalmed when we got 15,000 the other day, but it evens out, I guess. I did mention elsewhere that late Aug/early Sep sees a lot of variability in day-by-day melt.

I've done a new area/extent graph: http://img822.imageshack.us/img822/2060/areaoverextent210810.png
Not all that exciting, but one thing strikes. We got some big extent reductions at the beginning of August (reflected in the upwards kick in the 2010 line). I suggested when I posted it then (10th August version) that the ratio would drop again. Well, it did, but not as much as I expected. 2007 is the benchmark there as with pretty much everything else, and 2010 is still a lot more consolidated than 2007.

But although there hasn't been a dramatic spreading of the ice (lower ratio), the spreading has been prolonged. In 2008 this ratio started kicking up on 14/8, and the big extent reductions over the next month were at least partly due to compaction, not melt. 2009 bottomed out on 17/8 and 2007 on 21/8 - again, any extent reduction after than is partly compaction.

As at 21/8/2010, we haven't yet turned the corner. A relatively high proportion of whatever extent reduction we are seeing now is still genuine melt, not compaction. Now, it might turn the corner tomorrow, but at this stage it still looks like a relatively loose pack, which to me suggests more extent losses to come. 2008 has a couple of huge melts coming up (including a century on th 25th!), but if 2010 can hang tough, it might just nose ahead of 2008 before its all over. 2008 bottomed out on extent on 9/9, but I *think* 2010 will get maybe 10 days extra before it reaches minimum extent, which might make the difference.

(NB: "melt" above = in situ melt and ice exported out of the Arctic and melting in warmer waters.)

Werther

Logicman:
I wonder how the possible deterioration of the greenland icecap will be reflected in the coming months. Not that I assume it will be ready for media hype. But continuing a slow, perhaps unstoppable course. Now that we witness the last stages of summer sea ice retreat in the arctic, we may not have a complete grasp of what is happening. Maybe Cryosat-2 will give some answers in the coming months. I wonder if it will capture the whole picture. As all means of gathering information, it probably has its particular restrictions. It may measure surface height, bottom profile. It may provide a certain understanding of mass balance. But will it capture structural conditions within the icecap? As I glimpse over the broad melt zones this year, I see lots of torrential meltwaters, large pools, mellow white and grey colours probably indicating wet and soaking snow and ice. It may be that Lodger’s comments on the resistance of fresh, old sea-ice goes for ages-old land-ice too. In a way that it holds on to its external form, though internally the whole thing resembles an ever more delicate sponge-like structure. Neven’s link to the NASA picture of Lockerby-ice-island feeds that presentation of the margins of the icecap. Could Cryosat-2’s signals tell us anything about that? Or is it going to define ‘simple’ volume, giving a confusing response of the interior? Could a weakening sponge perform like a geological karst-formation? Like broad surfaces in the melt zone will more or less suddenly just collapse? A couple of years ago there was scientific talk of constant seismic activity through the icecap. I don’t hear much about that anymore. The last five years or so 200 Gigatonnes of meltwater a year keep trickling down, mechanically eroding its way. Maybe lubricating the bottom of the outlet-glaciers. Maybe adding to seawater-level some tenths of millimeters a year. Not really noticeable. Yet. But the Barnes icecap on Baffin island may give an indication. It shows little change in the situation of its limits. But look at all the gathering meltwater around its sides. You don’t notice that easily around Greenland, for the water is probably drained straight to the sea. I wonder if Logicman found time to do his announced study of the Greenland outlet glaciers. I don’t find the time. I’ll wait for the professional opinions… out of curiosity.

Werther

Sorry, maybe essays don't fit blogs... but then, for the occasional soul-mate

logicman

Werther:
My output has reduced to a trickle lately due to illness and to my focus on a forthcoming expose of a small group of professional climate change "experts".
I hope they like prison food. :-)

Moulins: if warm water trickles through ice it erodes the ice and transfers its heat energy into the ice. Also, falling water transfers its kinetic energy into the ice as heat. Warm water flowing out into the sea decreases local salinity and can affect horizontal and vertical circulation. A pulse of meltwater can clear melange and allow glacier calving. I think this may have happened before the 1st Jakobshavn calving. The 2nd calving - in my opinion - was triggered by the wash of the 1st calving.

As snow melts sooner and faster in the ice margins it fails to add mass to those areas. As the margins thin they can move faster.

Ice has a huge thermal capacity. What is important to examine is its residual thermal capacity. Consider ice at -0.5deg and ice at -5.0deg. The ice at -0.5deg has little residual thermal capacity. Accordingly a local temperature rise of only 0.6deg is enough to cause melting. Think of a night storage heater in reverse. You can keep sucking heat out of a storage cooler, but you can't keep pumping it in.

We need to know the temperature of the remaining sea ice. If it is close to zero then it will take very little sunshine, warm air or warm current to melt it. The ice circa 1900 would have been many meters thick and at least -30deg in the central ice cap.

Today? Average 1 meter thick? Average -2deg?

We need some boots-on-ice measurements.

Blatant plug:
My latest article is on economics and sustainable energy:
M.A.D. 2.0
http://www.science20.com/chatter_box/mad_20

Patrick.

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