High-latitude climate change in a global coupled oceanatmosphere-sea ice model with increased atmospheric CO₂

A global atmospheric general circulation model (GCM) coupled to a global 1-degree, 20-level ocean GCM with dynamic and thermodynamic sea ice is integrated with CO₂ increasing at 1% per year compounded for 75 years (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°C. The warm subsurface Atlantic layer at intermediate depths in the Arctic is maintained mainly by the sinking and intrusion of water from the West Spitsbergen Current in 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 400 m. This resembles an anomalous warm layer near those depths recently observed in the Arctic. As the climate warms and sea ice retreats, low clouds increase over the newly exposed water. Yet the consequent increase of cloud albedo over these regions is more than compensated for by the decrease of surface albedo due to the melting of sea ice. This produces a net decrease of planetary albedo in the Arctic that contributes to a strong ice-albedo feedback and the comparatively high sensitivity of the model.