Rising air temperatures, possibly the consequence of global warming, are melting the ice from above. (That's been the standard line.) Now, a British researcher has concluded that warmer water is also rising from the depths to attack the ice from below. His name is professor Peter Wadhams of the Scott Polar Research Institute in Cambridge.
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Arctic Ice Melting from Below
BBC News Online, Mar 27, 2002
Scientists believe they have identified a mechanism which can explain the thinning of the Arctic sea ice. They say the thinning, which in summer reaches more than 40% in some areas, has two causes. Rising air temperatures, possibly the consequence of global warming, are melting the ice from above. And warmer water is also rising from the depths to attack the ice from below. Professor Peter Wadhams, of the Scott Polar Research Institute in Cambridge, UK, said in 2000 that he had established the degree of thinning using measurements from submarines in 1976 and 1996. He said these showed that in that time a large area of the sea ice, stretching from the North Pole to the Fram Strait between Svalbard and Greenland, had thinned by 43% during the Arctic summer. US data from the other side of the Arctic, between the Pole and the Bering Strait, found a similar thinning over the same period.
The reported melting has been questioned by some scientists who believe the ice is still there, concentrated in areas where the submarines have not looked for it. But Professor Wadhams says the thinning he has detected, from 16ft (4.8m) 20 years ago to 9ft (2.7m) today, is scientifically explicable. He told BBC News Online: "People say global warming can't be raising air temperatures enough to melt the ice, because the Arctic winter temperature is around -30C anyway, and a one-degree warming would be irrelevant. But it's the summer temperatures that matter. Arctic summers are getting longer, so there is longer for the warmer air to melt the snow and affect the ice beneath. The other mechanism is the warming of one or two degrees in the water under the ice - enough to increase the bottom melting quite considerably. There is a cold water layer immediately beneath the ice. But that's changing its stability and salinity, because of changes in the distribution of Siberian river water in the Arctic. Over a large area that cold water is becoming more saline and denser, which means it's letting more heat rise through it."