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October 27, 2003
Seattle, Washington, USA

Variability and Trends in the Arctic Climate as Simulated with the Bergen Climate Model

Tore Furevik¹, Asgeir Sorteberg², Mats Bentsen³, Helge Drange⁴, Nils Gunnar Kvamstø^5
1Geophysial Institute, University of Bergen / Bjernes Centre , Allegt 70, Bergen, 5007, Norway, Phone 47-55-58-2691, Fax 47-55-58-9883, tore@gfi.uib.no
²Bjerknes Center for Climate Research, Allegt 70, Bergen, 5007, Norway, Phone 47-55-58-2693, Fax 47-55-58-9883, asgeir.sorteberg@gfi.uib.no
³Nansen Environmental and Remote Sensing Center, Edvard Griegs vei 3a, Bergen, N-5059, Norway, Phone 475-520-5875, Fax 475-520-5801, mats.bentsen@nersc.no
⁴G. C. Rieber Climate Institute, Nansen Environmental and Remote Sensing Center, Edv Greigsvei 3A, Bergen, N-5051, Norway, Phone 475-520-5875, Fax 475-520-5801, helge.drange@nrsc.no
⁵Geophysical Institute, University of Bergen, Allegt 70, Bergen, N-5007, Norway, Phone 475-558-2898, Fax 475-558-9883, nilsg@gfi.uib.no

The Bergen Climate Model (BCM) has been applied to perform a 5-member ensemble of 1% per year CO₂ increase experiments. Initial conditions have been taken from 300-years control integration with the BCM. Each experiment has been initialized at different strengths of the Atlantic Meridional Overturning Circulation (AMOC), and integrated for 80 years until doubled CO₂ is reached.

We will here present results from the control and perturbation simulations, with focus on the climate variability and trends of the Arctic. In the control integration, BCM realistically simulates the North Atlantic / Arctic Oscillation (NAO), and its observed impacts on sea-surface temperature and sea-ice distribution. In four out of five perturbation runs, NAO has a trend towards a more positive phase while in the fifth experiment, extremely negative values during the last decades, make the trend flat. Typically the NAO increase is in the order of 1 standard deviation during doubling of CO₂. At doubled CO₂, the annual ensemble mean shows 15% more precipitation in Arctic, and a warming of 3.5ºC. Both the changes and the spread in response among the different members are largest in wintertime. In all perturbation runs, the sea-ice area shows a steady decrease. After doubled CO₂, the winter ice maximum has retreated from the Barents Sea, and the entire Arctic is ice-free during summer. The strength of the AMOC has a negative trend in all members of the ensemble, with a typically decrease of 10 % over the 80 years. A similar reduction is not found in the inflow of Atlantic Water to the Nordic Seas. The Arctic climate response to the CO₂ increase is strong compared to what is found in other models. This is due to the additive effects of a small reduction in the AMOC and maintenance of the oceanic energy transport into the Arctic, increased NAO that increases the atmospheric energy transport into the Arctic, and the general warming due to increased CO₂.

Abstract Categories: Changes in the Atmosphere

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