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.
Scientists have been monitoring ongoing changes in Arctic sea ice for decades. By collecting samples of ice as well as a wide range of satellite-based data to document the changes, scientists find that Arctic sea ice is melting at an increasing rate. If the trend continues, Arctic sea ice may be gone by the year 2100. (Photograph courtesy NOAA Photo Library)
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.
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.
Bright white ice reflects sunlight from the Earth’s surface. In contrast, open water is very dark, and absorbs sunlight. As sea ice melts more water is exposed, which tends to increase warming. (Photograph courtesy NOAA Photo Library)