Arctic ice could start melting faster and faster, lifting sea levels and speeding the way to a warmer future, a new study suggests. 

2008-01-11

The old, thick ice that lasts year after year in the Arctic Ocean is giving way to younger, thinner ice that doesn't last the summer season, says James Maslanik, a researcher at the University of Colorado.

"This thinner, younger ice makes the Arctic much more susceptible to rapid melt," said Maslanik, of CU's Colorado Center for Astrodynamic Research. Each year the phenomenon makes it much more difficult to reestablish the sea ice conditions of the 1970s or 1980s.

Maslanik's study shows there has been a nearly complete loss of the oldest, thickest snow. Of the remaining perennial ice, 58 percent is only two or three years old.

Twenty-two years ago, only about a third of the ice was that young and thin.

Last year, CU's Snow and Ice Data Center announced that 2007 broke a record for the lowest extent of Arctic sea ice - and that it broke the record by 1 million square miles, an area about the size of Alaska and Texas combined.

The new study by Maslanik and his colleagues appears in this week's issue of Geophysical Research Letters.

The researchers used microwave, visible infrared radar and laser altimeter satellite data from NASA, the Department of Defense and the National Oceanic and Atmospheric Administration. They also used ocean buoys to measure and track sections of ice, 15 miles square, as they moved around the Arctic year after year on winds and currents.

The combination of warming, more solar radiation and the replacement of thicker ice with younger, thinner ice is "setting the Arctic up for additional significant melting" because all the factors feed back on each other, said Sheldon Drobot of CCAR.

"Taken together, these changes suggest that the Arctic Ocean is approaching a point where a return to pre-1990s ice conditions becomes increasingly difficult and where large, abrupt changes in summer ice cover as in 2007 may become the norm," the research team wrote.

Maslanik was in Barrow, Alaska, several years ago when he heard from an Inuit elder that they were losing a crucial supply of fresh drinking water.

When traveling or camping on the Arctic sea ice, Inuits for generations would use old ice floes as a source of drinking water, because the melted water is basically pure and fresh.

But recently, they'd had great trouble finding any ice that was old enough to have lost most of its brine content and become fresh water.

Maslanik resolved to look at the phenomenon in more detail - and over a larger area.

Each year that Arctic ice survives a summer melt cycle, it loses some of its salt content, and consequently gets stronger. Stronger that second year, it is less susceptible to melting and becomes stronger still.

Another reason older ice is stronger is that it changes its surface texture year after year. That way, it acts as a sort of snow fence, causing more wind-blown snow to accumulate on top of it, Maslanik said. Younger ice, by contrast, is typically smoother and flatter, so snow doesn't build up as much.

A third reason: Thinner layers of ice can easily slip on top of one another as they drift with wind and currents, leaving more and more of the Arctic Ocean completely free of ice, where it can absorb more heat and accelerate melting.

"If you cover your desk with dictionaries and try to push them into a pile, it's very difficult to do," because their thickness resists the sideways pressure, he said. But if you spread out playing cards on your desk - think thinner layers of ice - "you can easily push them into a much smaller pile."
That clears desk space. In the case of thin layers of ice, it clears ocean space and accelerates melting.

Meanwhile, another CU researcher warns that some glaciers on Greenland have doubled their ice discharge and speeds in the past decade.

The extent of the 2007 Greenland ice sheet melt broke the 2005 summer melt record by 10 percent, said Professor Konrad Steffen, director of CU's Cooperative Institute for Research in Environmental Sciences.

He and his team used a rotating laser and sophisticated cameras to transmit hourly data via satellites from 22 stations on the Greenland ice sheet.

Global sea rise could be faster than expected through the 21st century and beyond, he concluded in a talk last month to the American Geophysical Union.