Science Team Finds That Humans Probably Are Contributing to Retreat of Arctic Sea Ice

COLLEGE PARK, MD For the first time, scientists have placed satellite-derived observations of recent reductions in Arctic sea ice into a much longer-term context to show that sea ice decreases probably are due, at least in part, to human-caused climate change and that substantial decreases will probably continue in the future.

The findings, by a team of meteorologists, physicists, and climatologists from the University of Maryland, Rutgers University, NOAA, the University of Illinois, NASA, the Hadley Center in Great Britain, and the Arctic and Antarctic Research Institute in Russia, will appear in the December 3 issue of Science.

The team, led by Konstantin Vinnikov of the University of Maryland's department of meteorology, used computer climate models to examine whether the decreases observed in the ice cover of the Arctic over the past few decades are the result exclusively of natural climate changes or might also be influenced by human-induced global warming. First, observed satellite and ground-based data were used to measure the retreat of Arctic sea ice. Then the team used a computer model to simulate the changes in Arctic sea ice that would occur over 5,000-years of natural variation in climate if there was no human-added carbon dioxide in the atmosphere.

"Satellite data shows that from November 1978 through March 1998 there was an overall downward trend of 37,000 square kilometers per year in the extent of Arctic ice," said Vinnikov, a senior research scientist at Maryland. "Our computer modeling shows a less than 2 percent probability that natural variations in climate would produce such a large decrease over a period of only 19.4 years, suggesting that the negative trend is due to more than just natural variability."

The science team also examined outputs from computer simulations that include human- produced increases in carbon dioxide and aerosols. Carbon dioxide increases tend to warm the atmosphere, while aerosol increases tend to cool the atmosphere. The models that include these human-induced changes show a much better match with the observed sea ice decreases than the model simulating natural variability alone.

This suggests that melting Arctic sea ice is probably related to human-induced global warming, and that future decreases in sea ice extent can be predicted with some confidence using models that contain human-induced atmospheric changes, the scientists say.

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