Record amounts of the Arctic Ocean failed to freeze during the recent winter, new figures show, spelling disaster for wildlife and strengthening concerns that the region is locked into a destructive cycle of irreversible climate change.
Satellite measurements show the area covered by Arctic winter sea ice reached an all-time low in March, down some 300,000km2 on last year.
Scientists say that the decline highlights an alarming new trend, with recovery of the ice in winter no longer enough to compensate for increased melting in the summer. If the cycle continues, the Arctic Ocean could lose all ice earlier than expected, possibly by 2030.
Walt Meier, a researcher at the US National Snow and Ice Data Center in Colorado, said: "It's a pretty stark drop. In the winter the ice tends to be pretty stable, so the last three years, with this steady decline, really stick out."
Experts are worried because a long-term slow decline of ice around the North Pole seems to have accelerated since 2003, raising fears that the region may have passed one of the "tipping points" in global warming. In this scenario, warmer weather melts ice and drives temperatures higher because the dark water beneath absorbs more of the sun's radiation.
Meier said there was "a good chance" the Arctic tipping point has been reached.