A NASA satellite has documented startling changes in Arctic sea ice cover between 2004 and 2005.
The extent of «perennial» ice — thick ice which remains all year round — declined by 14%, losing an area the size of Pakistan or Turkey. The past few decades have seen ice cover shrink by about 0.7% per year.
The drastic shrinkage within a single year may relate partly to unusual wind patterns found in 2005, though rising temperatures in the Arctic could also be a factor. The Arctic is warming about twice as fast as the global average.
The research is reported in the journal Geophysical Research Letters.
Recent studies have shown that the area of the Arctic covered by ice each summer, and the ice thickness, have been shrinking. September 2005 saw the lowest recorded area of ice cover since 1978, when satellite records became available.
This latest study measures something slightly different from the extent of summer ice cover — the extent of «perennial» ice cover.
Perennial or «multi-year» ice is up to 3m thick and survives through at least one summer. It is different from «seasonal» ice, which is thinner and melts more easily, surviving for just one winter before succumbing to the summer sun.
If the pace of Arctic melting is quickening, the implications for the future are not reassuring. Ice reflects the sun’s energy back into space; open water absorbs it. So a planet with less ice warms faster, potentially turning the projected impacts of global warming into reality sooner than anticipated.
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