A critical minimum for Arctic sea ice can again be expected for late summer 2010, according to researchers.
Scientists from the Alfred Wegener Institute for Polar and Marine Research in the Helmholtz Association (AWI) in Bremerhaven and from KlimaCampus of the University of Hamburg have now published data in this context in the annual issue of Sea Ice Outlook. The online publication compares the forecasts on ice cover for September 2010 prepared by around a dozen international research institutes in a scientific "competition." The ice reaches its minimum area at this time every year.
The forecast developed by the team from KlimaCampus of the University of Hamburg, i.e. 4.7 million square kilometres (km2), is more negative than that submitted by the AWI researchers, who arrived at a figure of 5.2 million km2. Nevertheless, neither of the two research groups anticipates that the record minimum of 4.3 million km2 in 2007 will be reached.
Although Arctic ice currently has an area of ten million km2, which is half a million km2 smaller than in 2007, one cannot directly conclude a new record minimum in late summer. The present ice cover is comparable to that in June 2006, a year when more ice area remained in September than in 2007. The decisive factors for the situation in late summer, such as the ice thickness in the central Arctic and further development of the weather in summer, are not yet known, however.
There is no reason for an all-clear: scientists basically assume a long-term decrease in sea ice cover for the northern polar region in the summers of the coming decades. Even though the trend in terms of area points slightly upward (2007: 4.3 million km2, 2008: 4.68 million km2, 2009: 5.36 million km2), the Arctic ice area from 1980 to 1990 was constantly greater than seven million km2.
The two teams of scientists prepared their forecasts using different methods. Prof. Rüdiger Gerdes and his team from the Alfred Wegener Institute in conjunction with the scientific companies OASys and FastOpt jointly developed a model based on observation data from oceanic drift buoys and satellite data on ice measurement and ice movement. In the course of the summer the submitted forecast will be repeated on a monthly basis taking into account up-to-date weather data. "Currently we calculate that with 80% probability the ice cover in September will be between 4.7 and 5.7 million km2. However, the forecast will be more and more precise," says Prof. Rüdiger Gerdes.
The forecast developed by the KlimaCampus team headed by Prof. Lars Kaleschke, on the other hand, compares the ice area on every day of the year 2010 to that on the respective day from 2009 to 2003 on the basis of satellite pictures. The number and size of the ice-free areas, so-called polynyas, are indicators for later ice development. These dark ocean areas store solar energy already in early summer and thus additionally reinforce further melting during the polar summer, in which the sun no longer disappears, up to September.
For more information, see Sea Ice Outlook at http://www.arcus.org/search/seaiceoutlook/index.php
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