The drop in sea ice coverage—300,000 square kilometers—is roughly equivalent to the size of Italy (301,230 km²).

The Arctic sea ice shrinks during the summer and grows, or recovers, during the winter. The ice reaches its maximum extent during March, with a long-term (1979-2000) monthly mean extent of 15.7 million square kilometers (6.06 million square miles). Winter sea ice extent has begun to show a significant downward trend over the past four years.

The decline in summer sea ice extent from 1978-2005. The September trend from 1979 to 2005, now showing a decline of more than 8% per decade, is shown with a straight blue line.

However, NSIDC cautions that the winter recovery trend is not as striking as the sea ice minimum trend. In September 2005, the center reported a “stunning” reduction in arctic sea ice at the end of the northern summer. The persistence of near-record low extents led the group to conclude that Arctic sea ice is likely on an accelerating, long-term decline.

Changes in the sea ice minimum extent are especially important because more of the sun’s energy reaches Earth’s surface during the Arctic summer than during the Arctic winter. Sea ice reflects much of the sun’s radiation back into space, whereas dark ice-free ocean water absorbs more of the sun’s energy. Reduced sea ice during the sunnier summer months thus has more of an impact on the Arctic’s overall energy balance than reduced ice in the winter.

The lower winter extents are still important, however, because they reflect the pattern of reduced sea ice that scientists have already seen. Low winter recovery means that the ice is freezing up later in the fall and growing at a slower pace in the winter.

In an interview with the UK’s Guardian, Walt Meier, of the NSIDC said there was a “good chance” that the Arctic tipping point—the point at which warming begins a self-reinforcing acceleration—has been reached.

People have tried to think of ways we could get back to where we were. We keep going further and further into the hole, and it’s getting harder and harder to get out of it.