MAY BE this is Earth's way of telling President George W. Bush that global warming cannot be ignored: in just one year, the perennial sea ice cover in the Arctic Ocean has shrunk by nearly three-quarters of a million square kilometres, an area comparable to that of Bush's home state of Texas.

Perennial sea ice is the ice that survives at least one summer, and is usually more than 3 metres thick. Son Nghiem of the Jet Propulsion Laboratory in Pasadena, California, and his colleagues used NASA's QSCAT satellite to measure the changes in Arctic perennial ice from 2004 to 2005, by comparing ice cover averaged over November and December in each year, the team reports in Geophysical Research Letters (vol 33, p L17501).

They found that perennial ice cover decreased by 720,000 square kilometres - a 14 per cent drop in one year. This is a dramatic change compared with the 7.8 per cent reduction per decade that has been recorded since the 1970s.

The changes were not evenly spread. Perennial ice made some gains in the west Arctic Ocean, but nearly half was lost in the east. If the trend continues, it could open a vast ice-free region in the east Arctic Ocean, the team says.

From issue 2570 of New Scientist magazine, 23 September 2006, page 5