Summers in the Arctic may be nearly ice-free in as few as 30 years or even earlier, not at the end of the century as previously expected, according to a new study by a pair of researchers from the National Oceanic and Atmospheric Administration (NOAA) and the University of Washington. The updated forecast is the result of a new analysis of computer models coupled with the most recent summer ice measurements.
Scientists don’t expect the Arctic to become totally ice free, because ice will remain along northern Canada and Greenland. Powerful winds there sweep across the Arctic Ocean, forcing ice layers to slide on top of each other, building up a very thick ice cover.
“The Arctic is changing faster than anticipated,” said James Overland, an oceanographer at NOAA’s Pacific Marine Environmental Laboratory and co-author of the study, published 3 April in the journal Geophysical Research Letters. “It’s a combination of natural variability, along with warmer air and sea conditions caused by increased greenhouse gases.”
Overland and his co-author, Muyin Wang, a University of Washington research scientist with the Joint Institute for the Study of the Atmosphere and Ocean in Seattle, analyzed projections from six computer models. Wang says she and Overland chose models that accurately reflect the difference between summer and winter ice packs. That distinction demonstrates the model’s ability to take into account changing amounts of solar radiation. Among the six models fitting the researchers’ criteria, three have sophisticated sea-ice physics and dynamics capabilities. That data was then combined with observations of summer sea ice loss in 2007 and 2008.
The area covered by summer sea ice is expected to decline from its current 4.6 million square kilometers (about 2.8 million square miles) to about 1 million square kilometers (about 620,000 square miles)—a loss approximately four-fifths the size of the continental US.
Once the extent of ice at the end of summer drops to 4.6 million square kilometers—it was actually 4.3 million square kilometers in 2007 and 4.7 million in 2008—all six models show rapid sea-ice declines. Averaged together, the models point to a nearly ice-free Arctic in 32 years, with some of the models putting the event as early as 11 years from now.
Wang, M., and J. E. Overland (2009) A sea ice free summer Arctic within 30 years? Geophys. Res. Lett., 36, L07502, doi: 10.1029/2009GL037820