A new NASA-led study found a 23-percent loss in the extent of the Arctic’s thick, year-round sea ice cover during the past two winters. This drastic reduction of perennial winter sea ice is the primary cause of this summer’s fastest-ever sea ice retreat on record and subsequent smallest-ever extent of total Arctic coverage. …
Nghiem said the rapid decline in winter perennial ice the past two years was caused by unusual winds. "Unusual atmospheric conditions set up wind patterns that compressed the sea ice, loaded it into the Transpolar Drift Stream and then sped its flow out of the Arctic," he said. When that sea ice reached lower latitudes, it rapidly melted in the warmer waters.
"The winds causing this trend in ice reduction were set up by an unusual pattern of atmospheric pressure that began at the beginning of this century," Nghiem said.
The Arctic Ocean’s shift from perennial to seasonal ice is preconditioning the sea ice cover there for more efficient melting and further ice reductions each summer. The shift to seasonal ice decreases the reflectivity of Earth’s surface and allows more solar energy to be absorbed in the ice-ocean system.
Climate is complicated, so there may still be more to the phenomenon than we understand today, but certainly this is a more satisfying answer the "global warming" since Antarctic sea ice was hitting a 30 year high at the same time Arctic ice was at a 30-year low.
One of my favorite topics in climate discussion is "what is normal?" We have observed climate really intensely for maybe 30 years, and with any kind of reliable measurements for no more than about a hundred years. So given that climate moves in hundred thousand and million year cycles, how can we be sure our reference point, given 30 years of observation, is really "normal." One funny aspect of this is how often the headline has been flashed over the last few weeks that Arctic ice is at an "all-time" low. Really? You mean the lowest it has been in the 6 billion year history of earth? Well, no, just the lowest since 1979 when we started measuring by sattelite. (For those without a calculator, "since 1979" is really only 0.0000005% of "all-time.")
Update: Anthony Watt has much more