HIGH-LATITUDE CLIMATE-CHANGE IN A GLOBAL COUPLED OCEAN-ATMOSPHERE-SEAICE MODEL WITH INCREASED ATMOSPHERIC CO2

A global atmospheric general circulation model (GCM) coupled to a glob al 1-degree, 20-level ocean GCM with dynamic and thermodynamic sea ice is integrated with CO2 increasing at 1% per year compounded for 75 ye ars (CO2 doubles at about year 70). Flux correction is not used in the experiment. The increase of globally averaged surface air temperature at the time-of CO2 doubling is 3.8 degrees C. The warm subsurface Atl antic layer at intermediate depths in the Arctic, is maintained mainly by the sinking and intrusion of water from the West Spitsbergen Curre nt iii the model and the observations. With increased CO2 in the model , the warmer surface waters are intruded into the upper portion of the Atlantic layer producing an anomalous warming in the model at depths between 200 and 40 m. This resembles an anomalous warm layer near thos e depths recently observed in the Arctic. As the climate warms and sea ice retreats, low clouds increase over the newly exposed water. Yet t he consequent increase of cloud albedo over these regions is more than compensated for by the decrease df surface albedo due to the melting of sea ice. This produces a net decrease of planetary albedo in the Ar ctic that contributes to a strong ice-albedo feedback and the comparat ively high sensitivity of the model.