Ice levels had been tracking lower throughout much of 2008, but rapidly recovered in the last quarter. In fact, the rate of increase from September onward is the fastest rate of change on record, either upwards or downwards.

The data is being reported by the University of Illinois's Arctic Climate Research Center, and is derived from satellite observations of the Northern and Southern hemisphere polar regions.

Each year, millions of square kilometers of sea ice melt and refreeze. However, the mean ice anomaly -- defined as the seasonally-adjusted difference between the current value and the average from 1979-2000, varies much more slowly. That anomaly now stands at just under zero, a value identical to one recorded at the end of 1979, the year satellite record-keeping began.

Polar bear researchers fear recent effects of the loss of sea ice on Alaska polar bear populations. A 2006 study by the U.S. Geological Survey concluded that far fewer polar bear cubs in the Beaufort Sea were surviving and that adult males weighed less and had smaller skulls than those captured and measured two decades previously -- trends similar to observations in Canada's western Hudson Bay before a population drop.

A U.S. Geological Survey study completed last year as part of the petition process predicted polar bears in Alaska could be wiped out by 2050.