For years, scientists have been watching the Arctic Ocean with a mounting sense of unease. Sea ice on the very northern tip of our planet is melting - and it has been doing so much more quickly than expected.

By September 2007, in fact, the area in the Arctic covered by sea ice was only half as big as Europe, a 40 percent reduction from the mid-1990s, as calculated by the National Snow and Ice Data Center in the US. Glaciers on Greenland are likewise disappearing at an alarming rate. And the Arctic Ocean itself has been warming up since 1995, a trend that has only accelerated since the beginning of this decade. In the summer of 2007, water temperatures in the Bering Sea between Alaska and eastern Siberia were 5 degrees Celsius (9 degrees Fahrenheit) higher than average - warmer than ever before.