Sea Ice

Sea Ice Ends Year at Same Level as 1979

Thanks to a rapid rebound in recent months, global sea ice levels now equal those seen 29 years ago, when the year 1979 also drew to a close.

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.

Sea ice is floating and, unlike the massive ice sheets anchored to bedrock in Greenland and Antarctica, doesn't affect ocean levels. However, due to its transient nature, sea ice responds much faster to changes in temperature or precipitation and is therefore a useful barometer of changing conditions.

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