News Source: 
Phys.org
March 27, 2014

Scientists at the National Snow and Ice Data Centre (NSIDC), University College London, University of New Hampshire and University of Washington analysed 300 summer Arctic sea ice forecasts from 2008 to 2013 and found that forecasts are quite accurate when sea ice conditions are close to the downward trend that has been observed in Arctic sea ice for the last 30 years. However, forecasts are not so accurate when sea ice conditions are unusually higher or lower compared to this trend.

We found that in years when the sea ice extent departed strongly from the trend, such as in 2012 and 2013, predictions failed regardless of the method used to forecast the September sea ice extent," said Julienne Stroeve, a senior scientist at NSIDC and professor at University of College London. Stroeve is lead author of the study, published recently in Geophysical Research Letters.

"That downward trend reflects Arctic climate change, but the causes of yearly variations around the trend are harder to pin down," said Lawrence Hamilton, co-author and a researcher at the University of New Hampshire. "This collection of forecasts from many different sources highlights where they do well, and where more work is needed."
Arctic sea ice cover grows each winter as the sun sets for several months, and shrinks each summer as the sun rises higher in the northern sky. Each year, the Arctic sea ice reaches its minimum extent in September. Scientists consider Arctic sea ice as a sensitive climate indicator and track this minimum extent every year to see if any trends emerge.