Forecasts of Arctic’s summer ice coverage not yet reliable: study
"There is a need for better data for initialization of forecast models"
Will next year’s summer Arctic ice extent be low enough to allow ships navigate the Northwest Passage?
It’s hard to say, according to a new study that says year-to-year forecasts of the Arctic’s summer ice extent are not yet reliable.
As part of their research, scientists from the U.S. National Snow and Ice Data Centre, University College London and the Universities of New Hampshire and Washington looked at 300 summer Arctic sea ice forecasts from 2008 to 2013.
Forecasts, they found, are usually accurate when sea ice conditions are close to the downward trend that has been observed in the Arctic for the last 30 years.
But the study, called Predicting September Sea Ice Ensemble Skill of the Search Sea Ice Outlook 2008–2013 found the forecasts are less accurate when sea ice conditions are unusually higher or lower compared to that trend, making the causes of yearly variations around the trend harder to pin down.
“We found that in years when the sea ice departed strongly from the trend — such as in 2012 and 2013 — predictions failed regardless of this method used to forecast the September sea ice extent,” said Julienne Stroeve, a senior scientists at NSIDC and lead author of the study.
The collection of forecasts from many different sources highlights where this kind of research succeeds, the NSIDC said, but also where more work is needed.
Arctic sea ice cover grows through the winter months and shrinks each summer with the return of the sun, reaching its minimum extent each September.
Scientists consider sea ice a sensitive climate indicator and track this minimum extent each year to see if any trends emerge.
Satellite instrument shave been tracking sea ice coverage since 1979, showing a decline of about 13 per cent per decade.
Recent years have produced even more dramatic reductions in Arctic ice. In September 2012, sea ice reached a record minimum; 16 per cent lower than any previous September.
Long-term predictions of summer Arctic ice cover made global climate models suggest that the downward trend will lead to ice-free Arctic summers by the middle of the century.
Shorter-term forecasts are harder to make but are now in higher demand. Shrinking ice is a major consideration for communities in Nunavut and Nunavik, as well as industries interested in mining and shipping between Europe and Asia.
Many of the forecasts analyzed in the study focused on the quality of the ice cover ahead of the summer melt season. The NSIDC suggests that including sea ice thickness and concentration could improve seasonal forecasts.
“Short-term predications are achievable, but challenges remain in predicting anomalous years and there is a need for better data for initialization of forecast models,” Stroeve said.
“Of course there is always the issue that we cannot predict the weather, and summer weather patterns remain important.”
The study analyzed forecasts from the Study of Environmental Arctic Change Sea Ice Outlook, a project that gathers sea ice forecasts made by different researchers and prediction centres.