This might sound like an overly-fine distinction, but climate scientist Christina Hulbe argues for The Left Coaster that part of what is happening in the Arctic is a long-standing oscillation of systems called the "northern annular mode," or NAM. This oscillation is not enough to account for arctic ice melting without the "anthropogenic signal" (global warming) but it’s part of the story. She concludes:
In the end, the story here is not that the Arctic sea ice is retreating "faster than expected," as some news outlets have reported, but that it is retreating faster than climate models can simulate.
In response to a question from yours truly, she suggests (see the comments box, #26) that at this time next year the models will have been revised and re-run, and we should have a better sense of their ability to project changes in Arctic sea ice coverage.
Tom Toles has a slightly different view: