85% of Alaskan glaciers melting at 'incredible rate

Glaciers in Alaska are melting at "an incredible rate" according to US researchers. They report in Science today that 85% of the glaciers they examined had lost vast portions of their mass in the last 40 years. Some were now thinning at double the rates of the 1950s.

"Most glaciers have thinned several hundred feet at low elevation in the last 40 years and about 60 feet at higher elevations," said Keith Echelmayer of the University of Alaska at Fairbanks, who with four colleagues has systematically flown over 67 of Alaska's ice streams, and checked glacier thickness against measurements made by the US geological survey in the 1950s.

He calculated that at least 9% of the sea level rise in the last century could be explained by the melting of Alaska's glaciers. One glacier in southern Alaska - with an area bigger than the US state of Rhode Island - is surrendering 2.7 cubic kilometres of fresh water to the sea each year.

The scientists do not blame global warming - the shrinking of the glaciers, like the apparent retreat of sea ice around Antarctica, could be part of a local climatic cycle - but the discovery fits into the larger picture of a warmer world. Glaciers in the tropics - among them the snows of Kilimanjaro and the ice rivers high in the Andes - are melting so fast that they could disappear in the next 20 years.

The ice cover in the Arctic ocean itself is shrinking by an area the size of the Netherlands each year. The ice cap has also thinned from three metres on average, to two metres, in 30 years of nuclear submarine measurements. Ecologists have warned that Arctic bird populations are threatened, and that polar bear, seal and caribou poulations are losing their natural habitat.

Six of the 10 warmest years have been recorded in the last 10 years, the other four were in the 1980s. The growing season in Europe is now 11 days longer than it was 30 years ago.

There are around 160,000 glaciers on Earth. Only around 40 have been monitored closely in the last 20 years. But the glaciers of the high latitudes - Greenland, northern Canada, Alaska and Antarctica - are important in global warming calculations because the predicted warming will be greatest in the polar regions. Glaciers in Alaska and Canada cover 90,000 sq km, or 13% of the planet's mountain glaciers.

The team calculated that on average the glaciers were thinning at the rate of 1.8m a year, spilling an extra 96 cubic km of water into the oceans.