April
30, 2007 Arctic sea ice is melting at a significantly faster rate than projected by the most advanced computer models, a new study concludes. Scientists at the National Snow and Ice Data Center (NSIDC)
and the The study, "Arctic Sea Ice Decline: Faster Than Forecast?" will appear tomorrow in the online edition of Geophysical Research Letters (GRL). Julienne Stroeve of NSIDC led the study, with funding from NASA. NCAR’s principal sponsor is the National Science Foundation. The The study compared model simulations of late twentieth-century climate with observations. "This technique gives some indication of the realism of the simulated sea ice sensitivity to climate changes," said NCAR scientist Marika Holland, a co-author of the study. When the authors analyzed the IPCC computer model runs, they
found that, on
average, the models simulated a loss in September ice cover of 2.5
percent per
decade from 1953 to 2006. The fastest rate of September retreat in any
individual model simulation was 5.4 percent per decade. September marks
the
yearly minimum of sea ice in the "Because of this disparity, the shrinking of summertime ice is
about
thirty years ahead of the climate model projections," said NSIDC
scientist
and co-author Ted Scambos. This suggests that the The authors speculate that the computer models may fail to capture the full impact of increased carbon dioxide and other greenhouse gases in the atmosphere. Whereas the models indicate that about half of the ice loss from 1979 to 2006 was caused by increased greenhouse gases, and the other was half caused by natural variations in the climate system, the GRL study indicates that greenhouse gases may be playing a significantly higher role. There are a number of factors that may lead to the low rates of simulated sea ice loss. Several models overestimate the thickness of the present day sea ice and the models may also fail to capture changes in atmosphere and ocean circulation that transport heat to polar regions. Although the loss of ice for March is far less dramatic than the September loss, the models underestimate it by a wide margin, as well. "The actual rate of sea ice loss in March, about –1.8 percent per decade in the 1953 to 2006 period, was three times larger than the mean from the computer models," said Stroeve. March is typically the month when Arctic sea ice is at its most extensive. The "Our study indicates that the impacts of greenhouse gases on Arctic sea ice are strong and growing," said NSIDC scientist and co-author Mark Serreze.
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