Arctic sea ice melting much faster, experts find

Arctic summer sea ice is melting at a significantly faster rate than projected by even the most advanced computer models, according to a new study that concludes recent U.N. reports on warming underestimate the changes in the Arctic.

The shrinking of summertime ice is about 30 years ahead of the climate model projections, researchers with the National Center for Atmospheric Research and the University of Colorado's National Snow and Ice Data Center report in the online edition of the peer-reviewed journal Geophysical Research Letters.

The U.N.-sponsored Intergovernmental Panel on Climate Change had used data from the computer models to earlier this year release two reports on the state of Earth's climate. Citing earlier studies, the IPCC estimated that the Arctic could be free of summer sea ice somewhere between 2050 and 2100.

The new study, NSIDC researcher and lead author Julienne Stroeve said in a statement, "suggests that current model projections may in fact provide a conservative estimate of future Arctic change, and that the summer Arctic sea ice may disappear considerably earlier than IPCC projections."

NCAR scientist and co-author Marika Holland added that "while the ice is disappearing faster than the computer models indicate, both observations and the models point in the same direction: the Arctic is losing ice at an increasingly rapid pace and the impact of greenhouse gases is growing." 

While computer models are built to look forward, the authors ran them from a 1953 starting point and simulated, on average, a loss in September ice cover of 2.5 percent per decade through 2006.

The researchers then compared that to data taken from recent satellite measurements, as well as aircraft and ship reports, and found that the September ice actually declined at about 7.8 percent per decade.

Several possible factors were cited for the disparity:

• The models assume that half of the ice loss was due to increased greenhouse gases, but the study indicates those gases might play a significantly larger role.
• Several models overestimate the thickness of the present-day sea ice.
• The models might fail to fully capture changes in atmospheric and oceanic circulation that transport heat to polar regions.

A world without summer sea ice won't raise sea levels because that ice is already on water, not land. But it would have a huge impact on polar bears and other wildlife, as well as subsistence hunters. On the other hand, it would also open shorter sea routes, facilitating commerce.

The study was funded by the National Science Foundation and NASA.

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