Not surprisingly, no one has come up with the major cause for recent warming that they have evidence for that is an alternative to the human influence. I could keep repeating "what's the mechanism" and still get the empty void.
Meanwhile, Olivier, your observation of ice at the North Pole doesn't discount anything (though pretty interesting trip to take): the argument isn't that there's no ice there now, it's that it's melting faster than predicted (2013-2030 instead of 2100 for ice-free summers), as these articles that came out in 2007 and now Dec. 16, 2008 explain--notice the Navy is in on this too as well as the US Snow and Ice Research Center:
--[earlier article, 2007]
Professor Wieslaw Maslowski told an American Geophysical Union meeting that previous projections had underestimated the processes now driving ice loss.
Summer melting this year reduced the ice cover to 4.13 million sq km, the smallest ever extent in modern times.
Remarkably, this stunning low point was not even incorporated into the model runs of Professor Maslowski and his team, which used data sets from 1979 to 2004 to constrain their future projections.
[. . .]
Professor Peter Wadhams from Cambridge University, UK, is an expert on Arctic ice. He has used sonar data collected by Royal Navy submarines to show that the volume loss is outstripping even area withdrawal, which is in agreement with the model result of Professor Maslowski.
"Some models have not been taking proper account of the physical processes that go on," he commented.
"The ice is thinning faster than it is shrinking; and some modellers have been assuming the ice was a rather thick slab.
[. . .]
In the end, it will just melt away quite suddenly
Professor Peter Wadhams
"Our projection of 2013 for the removal of ice in summer is not accounting for the last two minima, in 2005 and 2007," the researcher from the Naval Postgraduate School, Monterey, California, explained to the BBC.
"So given that fact, you can argue that may be our projection of 2013 is already too conservative."
[. . .]
The US National Snow and Ice Data Center (NSIDC) collects the observational data on the extent of Arctic sea ice, delivering regular status bulletins. Its research scientist Dr Mark Serreze was asked to give one of the main lectures here at this year's AGU Fall Meeting.
Discussing the possibility for an open Arctic ocean in summer months, he told the meeting: "A few years ago, even I was thinking 2050, 2070, out beyond the year 2100, because that's what our models were telling us. But as we've seen, the models aren't fast enough right now; we are losing ice at a much more rapid rate.
"My thinking on this is that 2030 is not an unreasonable date to be thinking of."
http://news.bbc.co.uk/2/hi/science/nature/7139797.stm
--
And yes, of course the media hypes the more threatening date: 2013 instead of 2030. That's what sells papers.
"Arctic summers ice-free 'by 2013'" By the way, Olivier's pics clearly demonstrate the North Pole is as comfortable as any unheated swimming pool.
here's the more recent article:
"Scientists have found the first unequivocal evidence that the Arctic region is warming at a faster rate than the rest of the world at least a decade before it was predicted to happen."
[. . .]
The Arctic Ocean warmed more than usual because heat from the sun was absorbed more easily by the dark areas of open water compared to the highly reflective surface of a frozen sea. "Autumn 2008 saw very strong surface temperature anomalies over the areas where the sea ice was lost," Dr Stroeve told The Independent ahead of her presentation today.
"The observed autumn warming that we've seen over the Arctic Ocean, not just this year but over the past five years or so, represents Arctic amplification, the notion that rises in surface air temperatures in response to increased atmospheric greenhouse gas concentrations will be larger in the Arctic than elsewhere over the globe," she said. "The warming climate is leading to more open water in the Arctic Ocean. As these open water areas develop through spring and summer, they absorb most of the sun's energy, leading to ocean warming.
"In autumn, as the sun sets in the Arctic, most of the heat that was gained in the ocean during summer is released back to the atmosphere, acting to warm the atmosphere. It is this heat-release back to the atmosphere that gives us Arctic amplification."
Temperature readings for this October were significantly higher than normal across the entire Arctic region – between 3C and 5C above average – but some areas were dramatically higher. In the Beaufort Sea, north of Alaska, for instance, near-surface air temperatures were more than 7C higher than normal for this time of year. The scientists believe the only reasonable explanation for such high autumn readings is that the ocean heat accumulated during the summer because of the loss of sea ice is being released back into the atmosphere from the sea before winter sea ice has chance to reform.
"One of the reasons we focus on Arctic amplification is that it is a good test of greenhouse warming theory. Even our earliest climate models were telling us that we should see this Arctic amplification emerge as we lose the summer ice cover," Dr Stroeve said. "This is exactly what we are not starting to see in the observations. Simply put, it's a case of we hate to say we told you so, but we did," she added.
Computer models have also predicted totally ice-free summers in the Arctic by 2070, but many scientists now believe that the first ice-free summer could occur far earlier than this, perhaps within the next 20 years.
---
from:
just yesterday 912-16-08)--
http://www.independent.co.uk/environment/climate-change/arctic-melt-passes-the-point-of--no-return-1128197.html
