The Arctic influences European climate

Advanced climate model forecasts more frequent cold winters
A new ocean-atmosphere-model allows enhanced statements of climate sensitivity. Calculations of the reflected solar radiation were improved. This is obviously the most important factor for the polar amplification of global warming. The simulation demonstrates a significant change in weather patterns in the North Atlantic region. Dry and cold winter could occur more frequently than hitherto expected. The model was developed in cooperation of the Alfred Wegener Institute, the GKSS und further institutions within an EU-project.

Sun, ice and snow
Polar regions significantly influence the global climate : Ice surfaces have a high ability to reflect solar radiation, the albedo. Surfaces covered by ice are warming significantly less than uncovered surfaces. If global warming decreases the ice cover, the albedo will sink and thus enhance further warming. Possible future changes in Arctic sea-ice cover and thickness, and corresponding changes in the ice-snow-albedo-feedback, represent one of the major uncertainties in the prediction of future temperature change.

Improved sea-ice and snow albedo feedbacks were tested firstly in a regional Arctic climate model and then in a global model with a coupled atmosphere-ocean-sea-ice system. “Modelling 500 years takes about two months”, explains Andreas Benkel from the GKSS research centre. “Usually ten year fragments are simulated, then backuped and restarted.”

Global consequences of Arctic climate processes
Results of the modelling demonstrate that a change in the polar energy sink region can exert a strong influence on the North Atlantic Oscillation (NAO). The NAO is explained by fluctuations between the Iceland low pressure system in the northern, and the Azores high pressure area in the southern North Atlantic. A positive and a negative phase is distinguished. A stronger wets-east-current in the North Atlantic accompanies the fluctuations in air pressure in the positive phase. Thus more warm and humid air reaches northern and middle Europe. In the negative phase, the west-east-current is weakened and more cold polar air is transported to Europe. The actually observed warming in winter corresponds to changes in teleconnection patterns in NAO or Arctic Oscillation (AO)”, explains Prof Dr Klaus Dethloff from the Alfred Wegener Institute.“ This global pattern of air pressure and temperature distribution has changed drastically during the last five decades. This resulted in significantly warmer winter and slightly cooler summer periods.”

The improved model predicts a trend towards a negative NAO-phase. “The improved parameterization of the climate shows, that global patterns in the middle troposphere are similar to those of NAO and AO”, says Klaus Dethloff. Those fluctuations have a strong impact on the European climate. The strength of storms and their tracks are influenced. Cold and dry winters could occur more frequently.

Source: Geophysical Research Letters, February 2006

Contact: Prof Dr Klaus Dethloff (Tel. +49 (331) 288-2104; email: dethloff@awi-potsdam.de))

Bremerhaven, March 2nd, 2006