I have been following the amazingly rapid disappearance of Arctic sea ice for months at the University of Illinois Ice site.
Thursday, August 9, 2007 - New historic sea ice minimum
Today, the Northern Hemisphere sea ice area broke the record for the lowest recorded ice area in recorded history. The new record came a full month before the historic summer minimum typically occurs. There is still a month or more of melt likely this year. It is therefore almost certain that the previous 2005 record will be annihilated by the final 2007 annual minima closer to the end of this summer.
In previous record sea ice minima years, ice area anomalies were confined to certain sectors (N. Atlantic, Beaufort/Bering Sea, etc). The character of 2007's sea ice melt is unique in that it is dramatic and covers the entire Arctic sector. Atlantic, Pacific and even the central Arctic sectors are showing large negative sea ice area anomalies.
Arctic sea ice is disappearing far faster than previously predicted by models, with profound implications for climate change. The melt rate this summer has astonished the experts who study it.
William L. Chapman, who monitors the region at the University of Illinois Urbana-Champaign and posted a Web report on the ice retreat yesterday, said that only an abrupt change in conditions could prevent far more melting before the 24-hour sun of the boreal summer set in September. "The melting rate during June and July this year was simply incredible," Mr. Chapman said. "And then you’ve got this exposed black ocean soaking up sunlight and you wonder what, if anything, could cause it to reverse course."
Winds in the Arctic, have driven the sea ice from the shores of Alaska and Siberia towards the north Atlantic. The ice in contact with warm Atlantic water has melted extremely rapidly. A vast area of open ocean now extends from Siberia to Alaska (image).
The National Snow and Ice Data Center uses a longer time-averaging method than the Illinios researchers, so their investigators have not yet declared the sea ice levels an all time minimum.
While we use sea ice concentration data supplied by NASA via the National Snow and Ice Data Center (NSIDC), there are some differences between the way we and NSIDC process our sea ice indices. NSIDC uses 10-day running means; we use 3-day running means. NSIDC will often report sea ice extent indices and records, we are reporting a new sea ice minima sea ice area. The ice area metric includes year-to-year variations within the central pack ice and not just variations in the southern sea ice edge. Regardless of these differences, the rapid rate of sea ice melt this summer, along with the current negative sea ice anomalies almost guarantees a record Northern Hemisphere summer sea ice minimum this summer, by any metric.
However, the different averaging methods will only delay the minimum by a matter of days at the present rate of melting. And we cannot expect coming years to be more favorable for ice.
 The possibility of abrupt transitions in the future Arctic sea ice has consequences for the entire Arctic system.
Here we have shown that CCSM3 climate model projections suggest that abrupt changes in the summer Arctic sea ice cover are quite likely and can occur early in the 21st century, with the earliest event in approximately 2015.
These transitions are associated with an increased open water formation efficiency for a given melt rate as the ice thins. The surface albedo feedback accelerates the ice retreat as more solar radiation is absorbed in the surface ocean, increasing ice melt. Additionally, rapid increases in ocean heat transport to the Arctic generally lead and possibly trigger the events.
The loss of summer sea ice will likely have profound effects on global climate. Rapid warming in Europe and the Arctic may be amplified by the disappearance of summer ice. In the geologic record, [with similar environmental conditions to today but without sea ice] in the Pliocene, Europe and the Arctic were much warmer and wetter than today.
However, the rapid warming could contribute to the melting of the ice cap on Greenland, raising sea levels and freshening the north Atlantic waters. This could cause periods of sudden cooling. We don't yet have the capability to predict with confidence all of the effects of the loss of sea ice. The uncertainties are large.
The challenge to one part of the latest climate assessment by the Intergovernmental Panel on Climate Change (IPCC) "is not a question of whether the Earth is warming or whether it will continue to warm" under human influence, says atmospheric scientist Robert Charlson of the University of Washington, Seattle, one of three authors of a commentary published online last week in Nature Reports: Climate Change.
Instead, he and his co-authors argue that the simulation by 14 different climate models of the warming in the 20th century is not the reassuring success IPCC claims it to be. Future warming could be much worse than that modeling suggests, they say, or even more moderate. IPCC authors concede the group has a point, but they say their report--if you look in the right places--reflects the uncertainty the critics are pointing out.
A reason for serious concern with the unexpectedly rapid sea ice melting is the strong possibility that the IPCC has underepredicted the severity of climate change.