New record Arctic sea ice cover minimum? Climate researchers from Bremerhaven and Hamburg present new prognoses.

10.06.2009

Bremerhaven/Hamburg, June 10th 2009. Climate researchers from the Alfred Wegener Institute for Polar and Marine Research and KlimaCampus of the University of Hamburg participate for the second time in an international scientific competition. Some of the most renowned climate research institutes worldwide fathom possibilities for seasonal prognoses of Arctic sea ice cover by means of different methods and climate models. The declared aim of all participants is to find the best method for reliable prognoses. The German researchers agree upon a continuing negative trend. Another critical minimum of Arctic sea ice is to be expected in the late summer of 2009.

“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 % probability under that of 2007 - the year with the lowest-ever measured ice extension”, explains Prof. Dr. Rüdiger Gerdes from the Alfred Wegener Institute. “The new prognosis is to be repeated each month. It was developed in cooperation with staff from the scientific companies OASys and FastOpt (Hamburg) within the framework of the EU project DAMOCLES. The uncertainty of the prognosis is still very great because the Arctic melting period has just started. We expect increasing accuracy when the start date of the prognosis comes near to the target time period in September”, continues Gerdes.

The prognosis of the team from KlimaCampus of the University of Hamburg is slightly more positive: “We estimate a probability of 7 % that this year will fall below the negative record of 2007 - with an increasing tendency”, reports Prof. Dr. Lars Kaleschke from the Institute of Oceanography. There is no doubt regarding the long-term trend for him, too. “The Arctic sea ice will also melt extremely in this year - with far-reaching consequences for the global thermal and radiation balance.”

The researchers expect a long-term decrease of sea ice cover in the North Pole region in the summer of the coming decades. An exact prognosis for the respective next late summer is not possible, however. This is based on two factors: ice thickness at the end of the winter in its spatial distribution is unknown - in contrast to the degree of ice cover. “The knowledge of it, however, is of decisive importance for a good prognosis”, explains Gerdes from the Alfred Wegener Institute. In addition, a prognosis over the summer is made more difficult by the fact that the short-term development of sea ice is dependent on the actual weather over the Arctic Ocean. This is not predictable over many months, however.

Both research teams have approached this problem with different methods. Prof. Gerdes and his team have included additional measurement data into their model in this year. They utilized a data assimilation system developed by OASys and FastOpt within the framework of DAMOCLES. The simulation with their model (NAOSIM) orients itself on measurement data gained in the Arctic during the last months as closely as possible. Included are oceanic measurement data from drift buoys, such as brought out in the ice by the Alfred Wegener Institute, and also data on ice cover and ice movement measured from satellites. It is intended to take ice thickness measurements gained by the Alfred Wegener Institute and the Canadian University of Alberta with the research aircraft Polar 5 in later prognoses into account.

The prognosis of the Hamburg researchers around Prof. Lars Kaleschke is based upon an extrapolation of satellite data from the last 36 years. This is the longest global climate time series among 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”, reports Kaleschke. Different statistical prediction methods were tested. The most precise methodology is currently the analysis of the respective minima, this means the data from September regarding the whole time span. This shows the highest correspondence compared to real data measured later.

“Even if we do not wish a new record minimum of ice extent - we nevertheless hope that our prognosis will be near to the actual data in September, just like last year”, says Rüdiger Gerdes.

You can find information on the international scientific contest here: www.arcus.org/SEARCH/seaiceoutlook/index.php

You can find an animation regarding the current sea ice development from KlimaCampus Hamburg under www.youtube.com/watch (January 2000 - May 2009 in English) and here www.youtube.com/watch (January 2001 - September 2008 in German with an explanation).