Sept. 6, 2007 — Summertime sea ice in the Arctic Ocean is on track for shrinking by 40 percent below 1980 and 1990 levels by the year 2050, say oceanographers. That’s twice as fast as the rate of loss estimated in the most recent assessment by the Intergovernmental Panel on Climate Change (IPCC).

“This (is) a major change from the third IPCC report,” said oceanographer James Overland of the National Oceanographic and Atmospheric Administration. “This is moving the threshold up.”

Overland and his colleagues took a second look at how the 20 climate models used by the IPCC reproduced past sea ice changes due to global warming. They then threw away nine models that did poor jobs recreating real changes observed in the past few decades.

When they ran the remaining models together, there was a stark shift in the predictions: the amount of ice loss expected by the IPCC by the year 2100, the new test showed, will occur by 2050. A report on the study appears in the Sept. 8 issue of Geophysical Research Letters.

What it means, said Overland, is that in places like the north coast of Alaska, summer ice which was 30 to 50 miles offshore in the 1980s will be 300 to 500 miles away by 2050.

“It’s a huge effect on wildlife,” said marine biologist Jacqueline Grebmeier of the University of Tennessee in Knoxville. Grebmeier has spent the last two decades studying changes in ecology of the Bering Sea. “For the big animals that have to rest on ice, it’s a negative.”

For animals like walruses, which feed on clams and other shallow seafloor organisms, moving the ice to deeper waters effectively moves their grocery store out of reach. Other species already moving north with the ice and running into trouble are diving ducks, ringed seals and polar bears.

Opening the Arctic waters in summer has another effect on the ecology, she said. It allows plankton on the surface to eat up nutrients in the water that would, under ice, drop to the bottom to feed life there. In other words, more open water also effectively cuts off supplies to the walrus’s sea-bottom supermarket.

While the open waters may benefit shipping, Grebmeier is worried that vessels using a new Northwest Passage could bring more invasive species to the Arctic, further complicating the growing threats to Arctic natives.

“You’ll have winners and losers,” said Overland. A small bit of good news, he said, is the good chance that many of the channels in the Canadian archipelago will remain clogged with ice, leaving a refuge for Arctic species.

Source: Discovery

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