In 2007, when the summer melt season ended in mid-September, the extent of summer ice reached its lowest point in the satellite record, which goes back to 1979.
The '07 record didn't last long. In 2012, the melt-back of summer ice broke the '07 record – in the middle of the melt season. By the end of the season the extent of summer sea ice was 18 percent below the 2007 figure. The surviving ice patch – some 1.4 million square miles of it – had anchored one edge to the northern coasts of Greenland and Canada's Arctic Archipelago, leaving several hundred miles of open water between its seaward edges and the remaining Arctic coastlines of North America, Europe, and Asia.
The extent of melting in 2007 "caught pretty much everybody by surprise, because the retreat of the ice cover that summer was quite extreme," says Martin Jeffries, program officer and science advisor to the Office of Naval Research's Arctic and Global Prediction Program.
Despite the initial shock, however, the record melts of '07 and '12 arrived in the context of a persistent decline in summer sea ice throughout the 24-year satellite record.
The potential for a significant increase in maritime traffic in the Arctic basin each summer demands a better understanding of the ice cover and the factors that affect it in order to improve predictions.