The US National Snow and Ice Data Center (NSIDC) says the ice covered 4.5 million sq km (1.7 million sq miles) at its lowest point on 12 September. Last year’s minimum was 4.1 million sq km (1.6 million sq miles).
This summer’s ice cover was the second lowest since satellite records began 30 years ago, which NSIDC says emphasises the “strong negative trend”.
Temperatures have been lower in the Arctic this year than in 2007, largely because of La Nina conditions, which create a colder climate globally from their source in the Pacific. “I think this summer has been more remarkable than last year, in fact, because last year we had really optimal conditions to melt a lot of ice,” said Walt Meier, a research scientist at NSIDC in Boulder, Colorado.
“We had clear skies with the Sun blazing down, we had warm temperatures, and winds that pushed the ice edge northwards,” he told BBC News. “We didn’t have any of this this year, and yet we still came within 10% of the record; so people might be tempted to call it a recovery, but I don’t think that’s a good term, we’re still on a downwards trend towards ice-free Arctic summers.”
Even with cooler conditions anticipated, scientists had predicted at the beginning of the Arctic summer that last year’s record might be broken, because much of the ice was thinner than usual, having formed during only a single winter. Instead, the 2008 graph now appears to be indicating the beginning of an expansion from the 12 September minimum, as the Arctic autumn sets in.
The end of this summer will probably find the ice in a marginally healthier state than at this time last year. Some of the thin floes remaining will presumably thicken during the winter, leaving the ice a little more robust.
A few years ago, most computer models of climate were projecting dates about 80 years hence. Then, as the melt rate accelerated around the turn of the millennium, the projected date advanced to about 2040.
Now, some climate modellers expect to see nothing but open water within five years.
– from bbc