Just listened to a BBC "One Planet" documentary on the northwest passage. I knew that the Northwest passage was ice-free this summer for the fist time ever, but I didn't quite understand how big of a deal this was. I already understood less ice = more warming = less ice next summer, but I'll jsut quote David Bancroft's explanation. He's director of the Canadian Ice Service, which is the government agency responsible for monitoring sea ice.
DB: "I think it was some time around mid-august that I was looking at it and thinking that this was something out of a science-fiction setting. It's stunning. It's... I had no expectation of seeing this rapid a reduction in sea ice frankly for the next 10 years. There is no hint of this in the climate models for decades to come. And it happened in this last summer."
Interviewer: "Some scientists say this might be a kind of tipping point. Talk us through what you think."
DB: "It means that it can accelerate. The more open water you have in the summer time, the more sunshine gets trapped in the oceans, the more it warms up, and the faster it retreats. Eventually it can get to the point where there is no ice in the summertime. And the concern of some scientists is that we may have reached that point with the summer of 2007, where it's just going to retreat until there is no summer ice.
Interviewer: Now, there have been lots of forecasts for the date at which the Arctic in the summer would be ice free. It used to be 2100, and then 2080. How does this summer fit in to those forecasts?"
DB: "This point here [apparently pointing at one of the computer models they had displayed for this past summer] at the minimum ice that's shown, closely resembles what we see in the models or simulations of climate for the year 2040, on the worst case scenario [his emphasis, not mine.] So the summer of 2007 was stunning because it was decades ahead of where we expected to be in reduced sea ice."
Luckily 2008 is designated international polar year, so there will be a lot more research into this area of the earth, but we'd all better hope that the other climate models aren't also 35 years too conservative...