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The usual concern for Arctic sea ice crops up in the summertime, when the frightening ice decline results in more open water, and therefore a greater capacity for the dark Arctic Ocean to absorb the 24-hour sun’s heat - rather than reflect it back into space, as was the case when most of the Arctic surface was covered with bright, white ice.

But look at the state of Arctic ice now. Even as we approach the usual winter maximum, the ice extent is lower than at any time in recorded history, according to the National Snow and Ice Data Center in Boulder, Colorado. The Polar Science Center in Seattle reports that ice volume also continues its decline, or should I say, collapse - at unprecedented speed, to unprecedented lows.

Thus, despite the calls from d’oh-headed deniers like Art Horn for a global chill driven by a “super La Nina,” we have a year that wraps up tied as the warmest ever and a continuing trend that indicates the coming summer will feature the effects of redoubling climate feedbacks.

We stand in awe of the DenierGang’s ability to tie themselves up in logical knots and we await their next falacious analysis with unfailing interest.

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Two graphs, inluding the brand new one to the left, show two (mutually affirming) analyses of the trajectory of Arctic sea ice over the last 30 years.

The National Snow and Ice Data Center graph (left) shows Average Monthly Sea Ice Extent. The figure below shows a Polar Science Center model-generated calculation of Sea Ice Volume. Notwithstanding that NSIDC reports Arctic temperatures in October were 4 to 6 degrees Celsius (7 to 10 degrees Fahrenheit) higher than normal, there is something chilling in the similarity of the two graphs. 

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Update: NSIDC pinpoints Sept. 19 as date of least Arctic ice extent in 2010

Arctic Sea Ice Extent, which the National Snow and Ice Data Center (NSIDC) in Boulder, Co., announced had reached its annual minimum on Sept. 10, has now slipped even further, to a point that could be below the 2008 minimum. That would make this the second lowest summer ice cover in recorded history.

“It’s awfully close (to the 2008 low),” NSIDC research scientist Dr. Walt Meier said on Wednesday (Sept. 22, 2010). “And even though the air temperatures are getting colder, the ocean has a lot of heat in it and can continue to melt ice.”

Meier acknowledged that the NSIDC jumped the gun in announcing the apparent annual minimum. The ice extent had been increasing for three consecutive days and the scientists assumed the season had turned. But much of the ice is broken up and thin, conditions that mean “it doesn’t take a lot to get late season melting,” Meier said.

Ice watchers may be more concerned, however, by the inset Polar Science Center graph of ice volume, which shows that the total amount of ice (as differentiated from the extent of the Arctic ice cover) has dropped off a cliff.

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Wondering whether weather indicates climate

The latest graph tracking un unprecedented plunge in Arctic sea ice measurements raises once again the question of when you can look at a weather event - a dramatic and unprecedented weather event - and make a relevant and reasonable assumption about what is happening to the climate.

Given the enthusiasm that the denier community brings to challenging assumptions at the contestable edge of science, I’d be wary about saying, unequivally, that this graph shows climate change in action. It’s only part of one year’s data. Admittedly, it’s compared to an average over a much longer time, but it’s still just one year. That’s why you might want to look at the next graph:

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No Records Broken Today: Climate Change Called Off

It is legitimate to criticize people who use a single weather event to bolster their case for concern about global warming. But how much more bizarre is it to seize upon a single soggy summer (this one) in a very narrow part of the world (Toronto) to argue the opposite?

The purple proseur Rex Murphy did just that in his Globe and Mail column (“So where’s the global cooling alert?”) a week ago. He wanted to know why we had not all cancelled the climate change alarm on account of Toronto’s unusually wet and chilly summer weather. Noting the likelihood that record-breaking hot weather moves people to discuss the risks and evidence of global warming, Murphy says:

Now, however, Toronto in July is cool and I am waiting in vain for the lips of just one forecaster to ask how can this be. Waiting just once to hear the familiar phrase “global warming” in a sentence that even hints that the theory behind it is so much more tentative than we have been urged with such fervour to believe.

It’s a little like ending an uneventful motorcycle ride with the conclusion that there is - quite apparently - no longer any danger to cycling and that helmet legislation should be repealed.

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Arctic ice has maxed out for the year and is starting its slow melt into summer in much worse shape than normal, according to the National Snow and Ice Data Centre.

If you look only at the extent of Arctic sea ice, things are not as bad as they have been in recent years. Ice cover is five per cent higher this year than in the record low 2006, even if it is four per cent lower than the 1979 to 2000 average.

But ice thickness is another story, and that seems to be all bad news.