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.
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Continuous scatterometer data has been available only since 1999, so for comparison researchers must use the records of summer ice extent - which is almost, but not exactly, the same thing as perennial ice extent.
"If we average that over the long term we find a reduction of between 6.4% and 7.8% per decade," said Dr Nghiem. "What we have here is 14% in one year - 18 times the previous rate."
The key questions are what caused it, and whether it is an anomaly or the first sign of a major change of pace for Arctic melting.
