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An iceberg melting in Svalbard, in the Norwegian Arctic.

(© picture-alliance/Balance/Photoshot)

Expert teams from the Alfred Wegener Institute for Polar and Marine Research and the KlimaCampus at the University of Hamburg participated in an international science competition aimed at finding the best method for forecasting Arctic sea ice loss.

Experts attribute the rapid ice loss to global warming and predicting its trend sheds light on the pattern. Although an exact prognosis is impossible, the researchers predict a long-term, sustained decrease of Arctic sea ice cover during the summers in the coming decades.

"We have computed in this year's first prognosis that the ice cover of the Arctic Ocean will lie at the end of the summer with 28 percent probability under that of 2007 - the year with the lowest-ever measured ice extension," says Rüdiger Gerdes of the Bremerhaven-based Alfred Wegener Institute.

The forecast was developed together with experts from the science firms OASys and FastOpt (Hamburg) for the European Union research project DAMOCLES.

Its uncertainty is due to the fact that the Arctic melting period has just begun. Yet its accuracy will improve, according to Gerdes, over time as the target period in September 2009 approaches.

The KlimaCampus prognosis, however, forecasts that there will be less ice loss.

"We estimate a probability of 7 percent that this year will fall below the negative record of 2007 - with an increasing tendency," explains Lars Kaleschke from the Institute of Oceanography.

The end result is almost certain for Kaleschke: "The Arctic sea ice will also melt extremely in this year - with far-reaching consequences for the global thermal and radiation balance."

The certainty of the predictions is difficult because it is unknown how ice thickness is distributed at the end of the winter, as opposed to the degree of ice cover.

The prognosis is moreover hindered because the development of sea ice over the short term depends on the weather over the Arctic Ocean, which is not predictable over many months.

To account for this improbability, Professor Gerdes and his AWI team have included additional measurement data in their model, using data assimilation systems. Their simulation is based on measurement data gained in the Arctic over the past few months, including ocean measurements from buoys brought out on the ice by an AWI team, as well as satellite collected data of the ice cover.

The AWI 2008 prognosis was very near to the actual result.

The Hamburg research team came to their forecasts by extrapolating on satellite data gained over the last 36 years. This is the longest climate time series of all satellite measurements.

"Our latest studies show that there is no conclusive interrelation between the frozen surface measured in the winter and in spring and the expected minimum for the late summer," explains Kaleschke.