Arctic Ice Melting Much Faster Than Predicted

Richard A. Lovett
for National Geographic News

May 1, 2007

Arctic Ocean sea ice is melting faster than even the most advanced climate change models predict, a new study concludes.

The work, published today in the journal Geophysical Research Letters, used the models to retroactively predict sea-ice decline from 1953 to 2006.

Scientists then compared the results to what has actually been recorded by Earth-based and satellite observations during that time frame.

The team found that, on average, 18 climate models used in a 2007 report by the Intergovernmental Panel on Climate Change (IPCC) underestimated the extent of sea-ice decline by a factor of three.

"We're about 30 years ahead of what the models show," said Julienne Stroeve, lead author of the study and a researcher at the National Snow and Ice Data Center at the University of Colorado in Boulder.

The IPCC report projects that the Arctic Ocean will retain some ice year-round until about 2050, after which time the region will be ice-free during the summers.

(Read a related report: "Arctic Summers Ice Free by 2040, Study Predicts" [December 12, 2006].)

But the new findings mean that the ocean could lose its summer sea ice much sooner, Stroeve said.

Not Natural?

The new work is an important test of existing climate models, said Steven Running, a professor of ecology at the University of Montana who was not involved in the study.

Mapping sea ice by satellite is currently one of the best tools for measuring the effects of global warming, he said in an email.

"White ice is easily distinguished from nearly black water," in the satellite images, Running said.

Study author Stroeve believes that the models underestimate the effect of ocean currents carrying ever warmer water into the Arctic Ocean from the Atlantic and Pacific.

"The models don't handle ocean processes quite so well," she said. "This is playing a larger role than we thought."

Still, she added, all the models make it clear that human-caused emissions of carbon dioxide and other atmosphere-warming gases are a major factor in Arctic melting.

"It is highly unlikely that this is natural variability," she said. "I believe this is happening because of changes in our atmosphere" caused by human activities.

The findings ratchet up concerns for Arctic wildlife and the livelihoods of Arctic residents.

"And the [existing] predictions were worrisome enough," said Walter Oechel of the Global Change Research Group at San Diego State University, who was not involved in the new study.

The finding is simply another indicator that earlier predictions about the impact of global warming weren't overly alarmist, Oechel added.

"What we're finding is that most of the estimates are holding up or occurring at an accelerated rate," he said.

"If any mistakes were made, it's that the estimates were overly conservative."

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