The melting of the Arctic sea ice literally crossed another line yesterday, as the area of Arctic sea ice fell below the level of two years ago:
The collapse of the Arctic sea this year is only surpassed by the calamity of 2007. The four lowest years of Arctic sea ice extent are the last four years. The extent of Arctic sea ice observed yesterday is about four standard deviations below the 1979-2000 mean for that calendar day: current ice conditions are only 0.01% likely to be observed as a random event, assuming that the classic climate pattern seen in the 1979-2000 average still holds. Nothing is certain in a probabilistic science like climatology, but the existence of a climate shift here is about as close to certain as you can get.
As of yesterday, the extent of sea ice in the Arctic is still falling.