Arctic ice extent -- lower than average

From the National Snow and Ice Data Center, a revealing graphic: Arctic sea ice reached its yearly maximum extent during the second week of March, 2008. Maximum extent was slightly greater compared to recent years, but was still well below average.

Despite strong growth of new ice over the winter, sea ice is still in a general state of decline. The ice that grew over the past winter is relatively thin, first-year ice that is susceptible to melting away during the summer. Although natural variability in the atmospheric circulation could prevent the ice pack from breaking last year's summer record, a closer look at sea ice conditions indicates that the September 2008 minimum extent will almost certainly be well below average.

Arctic sea ice extent for March 2008, the winter maximum, was 15.2 million square kilometers (5.9 million square miles). The magenta line shows the median ice extent for March from 1979 to 2000. Please note that our daily sea ice images, derived from microwave measurements, may show spurious pixels in areas where sea ice may not be present. These artifacts are generally caused by coastline effects, or less commonly by severe weather. Scientists use masks to minimize the number of "noise" pixels, based on long-term extent patterns. Noise is largely eliminated in the process of generating monthly averages, our standard measurement for analyzing interannual trends. Data derived from Sea Ice Index data set.

Graphic credit: National Snow and Ice Data Center