Ice extent, March 2010 (purple line=median).

The Arctic’s sea ice has grown as big as it is going to get this year, according to the US National Snow and Ice Data Center.

In early March it appeared sea ice had reached its maximum extent and started to decline, but the cold snap came in and the ice started to grow again. The real maximum extent of 15.25 million square kilometres was reached on 31 March, the latest date for the ice maximum since satellite records began in 1979, NSIDC announced today.

This year’s ice area is 650,000 square kilometres down on the average for the years 1979 to 2000, although it is a similar amount up on the record low of 2006.

Mark Serreze, director of NSIDC, says that a system of opposing atmospheric pressures in the northern middle and high latitudes known as the Arctic Oscillation is to blame for this year’s strange ice.

“It has been a crazy winter with Arctic ice cover growing and very cold weather in northern Europe and eastern America all linked to this strongly negative Arctic Oscillation,” he told the Times.

In other ice news, NASA’s Operation IceBridge has seen stretches of open water in the sea ice during flights surveying the Northwest Passage (image below).

Ice map: NSIDC / Photo: NASA/Jim Yungel