Further evidence that the IPCC has been conservative in it's conclusions. From Reuters:

The Arctic ice cap is melting much faster than expected and is now about 30 years ahead of predictions made by the Intergovernmental Panel on Climate Change, a U.S. ice expert said Tuesday.

This means the ocean at the top of the world could be free or nearly free of summer ice by 2020, three decades sooner than the global panel's gloomiest forecast of 2050.

No ice on the Arctic Ocean during summer would be a major spur to global warming, said Ted Scambos, a glaciologist at the National Snow and Ice Center in Colorado.

"Right now ... the Arctic helps keep the Earth cool," Scambos said in a telephone interview. "Without that Arctic ice, or with much less of it, the Earth will warm much faster."

This is a really scary example of positive feedback loops. A big concern here is that similar melting would occur on the Greenland ice sheet, thereby driving up sea levels.