Contemplating a warmer Arctic

If recent warming of the north continues, the sea ice that floats on the Arctic Ocean each summer will disappear by the year 2100, and there doesn’t appear to be any natural switch to turn off the change, according to a group of more than 20 scientists.

“By the end of the century, if we don’t do anything about greenhouse gases, (the Arctic Ocean) will certainly be open,” said Jonathan Overpeck of the University of Arizona, the first author on an article in the American Geophysical Union’s weekly newspaper, "EOS," on August 23. 2005. The article has 20 coauthors, including four Alaska scientists.

Matthew Sturm of Cold Regions Research and Engineering Laboratory in Fairbanks was one of a diverse group of scientists who gathered in Big Sky, Montana two years ago to ponder what the far north would look like if the summer ice cover of the Arctic Ocean disappears. Sturm studies snow and shrubs on Alaska’s North Slope. Also at the meeting were oceanographers, permafrost scientists, sea-ice experts, studiers of treeline movement, anthropologists, and biologists. They spent a week learning about one another’s research and in the end hammered out a paper that became the basis of the "EOS" article.

The scientists combined the evidence of all their studies and concluded that the north was getting warmer and they didn’t see any natural mechanism that might reverse the trend.

“There’s a lot of things that could amplify the change but not many that can hold it back,” Sturm said. “The Arctic system gets much simpler without summer ice; we no longer will have a complicated ocean/sea ice interaction in summer, but the ramifications of those changes are anything but simple. When you begin to change a system this profoundly, everything changes.”

The icepack on the Arctic Ocean has existed for at least the last 800,000 years, said Overpeck, whose studies in the Arctic involve taking cores of lakebeds to look for ancient pollen grains and other indicators of what the north looked like long ago.

“The current trajectory is taking us into uncharted ground,” Sturm said.

Some scientists at the week-long retreat were more cautious about the results. Richard Moritz of the University of Washington’s Polar Science Center said he wanted the group to subject the notion that the far north was on a warmer path to a test that might further validate the likelihood of an ice-free Arctic Ocean.

“I thought if we were going to use terminology like ‘trajectory’ we ought to have some kind of mathematical model to demonstrate what we were talking about,” he said. “We also don’t know how much of the recent trend is human-forced, although it seems clear that human forcing has made some contribution.”

In the article, the researchers wrote that the changes “appear to be driven by both natural variability and (manmade) forcing.”

However the changes are caused, scientists worry that some of the effects are irreversible.

“There are thresholds that, when crossed, you can’t come back,” Overpeck said.

Thawed permafrost and increased fresh water that drives ocean circulation patterns are two examples Overpeck spoke of over the phone.

One might wonder if there is any good news for residents of the far north, who, as the authors wrote, “produce only a minor amount of the trace gases, yet (are) experiencing a disproportionate impact of the consequences.”

Larry Hinzman, a hydrologist with the University of Alaska Fairbanks Water and Environmental Research Center also attended the Big Sky meeting. He said that Earth’s natural resiliency is something people don’t talk about much, but is evident in records of recovery from past ice ages and warm periods.

“The Earth has taken a lot of punches in the past and so have people,” he said. “We can adapt to changes, we just don’t like doing it.”