Ice Retreating 30 Years Ahead of Projections

Ice Retreating 30 Years Ahead of Projections



   
April 2007 -   Arctic sea ice is 
melting much more quickly than projected by even the most 
advanced computer models, a new government funded study has 
found. Comparing actual ice observations with climate models, 
the scientists conclude that the Arctic could be seasonally 
free of sea ice as early as 2020. 
Scientists at the National Center for Atmospheric Research and 
the University of Colorado's National Snow and Ice Data Center 
have demonstrated that the Arctic's ice cover is retreating 
more rapidly than estimated by any of the 18 computer models 
used by the Intergovernmental Panel on Climate Change in 
preparing its 2007 assessments. 
"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," says 
co-author Marika Holland of the National Center for 
Atmospheric Research, NCAR. Arctic Ocean sea ice breaking up in March 
Whereas the computer models indicate that about half of the 
ice loss from 1979 to 2006 was due to increased greenhouse 
gases, and the other half due to natural variations in the 
climate system, the new study indicates that greenhouse gases 
may be playing a significantly greater role. 
The study, "Arctic Sea Ice Decline: Faster Than Forecast?" 
will appear Tuesday in the online edition of "Geophysical 
Research Letters." It was led by Julienne Stroeve of the 
National Snow and Ice Data Center and funded by the National 
Science Foundation and by NASA. 
The authors arrived at their conclusions by comparing model 
simulations of past Arctic climate and sea ice conditions with 
observations by satellites and other instruments. 
Satellites have flown over the Arctic and looked at sea ice 
since 1978. Some sea ice melts in the summer every year, even 
in the Arctic, where temperatures are still near freezing. But 
in 2002, satellites showed that the springtime melting of sea 
ice started earlier than normal. 
Satellites helped scientists learn that there was about 
502,000 square miles less sea ice each September since 2001 
than there typically was in previous Septembers. September 
marks the yearly minimum of sea ice in the Arctic. 
Stroeve and her team 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 
was 5.4 percent per decade. 
But newly available data sets, blending early aircraft and 
ship reports with more recent satellite measurements that are 
considered more reliable than the earlier records, show that 
the September ice actually declined at a rate of about 7.8 
percent per decade during the 1953-2006 period. 
"This 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," says Stroeve. 
The study indicates that, because of the disparity between the 
computer models and actual observations, the shrinking of 
summertime ice is about 30 years ahead of the climate model 
projections. 
This figure illustrates how much faster Arctic sea ice is 
melting than computer models project. The dotted line 
represents the average rate of melting shown by computer 
models. The blue area shows the spread among the different 
models. The red line shows the actual rate of Arctic ice loss 
based on observations. (Illustration by Steve Deyo, ©UCAR)
As a result, the Arctic could be seasonally free of sea ice 
earlier than the timeframe projected by the Intergovernmental 
Panel on Climate Change, which said the ice would disappear 
any time from 2050 to well beyond 2100. 
March is typically the month when Arctic sea ice is at its 
most extenvironment newsive. The researchers found that 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 study concludes that the actual rate of sea ice loss in 
March, which averaged about 1.8 percent per decade in the 
1953-2006 period, was three times larger than the mean from 
the computer models. The Arctic is especially senvironment newsitive to 
climate change partly because regions of sea ice, which 
reflect sunlight back into space and provide a cooling impact, 
are disappearing. In contrast, darker areas of open water, 
which are expanding, absorb sunlight and increase 
temperatures. 
This feedback loop has played a role in the increasingly rapid 
loss of ice in recent years, which accelerated to 9.1 percent 
per decade from 1979 to 2006, according to satellite 
observations. 
Scientist Julienne Strove with the University of Colorado's 
National Snow and Ice Data Center 
In a separate study released in March, Stroeve and her team 
showed that dwindling Arctic sea ice may have reached "a 
tipping point that could trigger a cascade of climate change 
reaching into Earth's temperate regions." 
The loss of Arctic sea ice is most often tied to negative 
effects on wildlife like polar bears and increasing erosion of 
coastlines in Alaska and Siberia. Other studies have linked 
Arctic sea ice loss to changes in atmospheric patterns that 
cause increased precipitation over western and southern 
Europe. 
The decline in Arctic sea ice could impact western states like 
Colorado by reducing the severity of Arctic cold fronts 
dropping into the West and reducing snowfall, impacting the 
ski industry and agriculture.
 
Native communities in the Arctic are being affect by changes 
in the extent and duration of sea ice cover, and the increase 
in contaminant burdenvironment news in subsistence foods that threaten 
hunting traditions and human health.
 
The low rates of simulated sea ice loss were projected by 
climate models, the researchers say, because several models 
overestimate the thickness of the present-day sea ice and the 
models also may fail to fully capture changes in atmospheric 
and oceanic circulation that transport heat to polar regions. 
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. 

---