In 2002, a series of scientific studies pointed to dramatic changes in Arctic sea ice. Sea ice that survives the summer and remains year round—called perennial sea ice—is melting at the alarming rate of 9 percent per decade, according to a study by NASA Goddard Space Flight Center senior researcher Josefino Comiso. The extent of Arctic sea ice at summer’s end reached a record low in 2002, reported NASA-funded researchers at the University of Colorado’s National Snow and Ice Data Center, in Boulder. Early findings suggest that summertime melting of Arctic sea ice in 2003 is on pace to rival last year’s low.
 

In support of this evidence of a changing Arctic climate, Comiso shows in a new paper that most of the Arctic warmed significantly in the 1990s compared to the 1980s. The study also finds that the seasons when sea ice melts, between early spring and late fall, have gotten longer and warmer each decade, and that Arctic regions within North America have warmed more per decade than other Arctic areas. The study, which appears in the November 1 issue of the American Meteorological Society’s Journal of Climate, uses surface temperature data taken from satellites between 1981 and 2001.
 

It is tempting to take solace in the idea that these striking changes are happening somewhere far away. But in reality, such shifts in the Arctic are likely early indications of a global climate in a state of flux. “People talk about global warming, and the Arctic really is the best place to detect global warming because the effects are amplified there,” Comiso says.

The reasons why climate changes get amplified in the Arctic are many and complex, but one of the main features concerns the ice itself. Ice reflects the Sun’s rays up into the atmosphere and out to space, which keeps solar radiation from warming the Arctic lands and ocean. Both sea ice, which floats on water, and glaciers and ice on land cool the Earth in this manner. Without large ice masses at the poles the Earth would absorb more heat and warming would escalate. When ocean temperature rises sea ice becomes thinner, exposing more water, thus reinforcing the warming trend and creating a positive feedback loop.
 

The Arctic is warming at an accelerating rate. Satellite data collected from 1981 to 2001 show that some regions are warming faster than 2.5 degrees Celsius per decade. In this map, red colors show areas of warming, blue shows areas of cooling, and white represents little or no change. (Map adapted from Josefino Comiso)

This animation shows annual temperature anomalies in the Arctic from 1981 to 2003. The anomalies range from 7 degrees below normal (dark blue) to 7 degrees above normal (dark red). (Animation courtesy Cindy Starr, NASA GSFC Scientific Visualization Studio)

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Researchers suspect that loss of Arctic sea ice may be caused partly by global warming and partly by changing atmospheric pressure and wind patterns over the Arctic that move sea ice around, which also help to warm Arctic temperatures. Changes in air pressure and wind patterns may likewise be a result of greenhouse gas buildup in the atmosphere.

“The warming we see is another indication that climate is now changing, and in ways that may not have been experienced in several million years,” says David Rind, a senior researcher at the NASA Goddard Institute for Space Studies in New York.

 Ice at a Threshold?

The data used in this study are available in one or more of NASA's Earth Science Data Centers.