Modeling feedbacks in the Arctic climate system (Invited Presentation)

There are many complex interactions and feedbacks among the components of the climate system in the Arctic region. Global climate models indicate that these feedbacks will lead to enhanced winter increases of Arctic surface air temperature relative to the global average in response to increasing atmospheric greenhouse gases. Two 150-year simulations of a global climate model are used to examine how the Arctic Ocean energy budget and water budget might change if atmospheric greenhouse gases (GHGs) increase. One is a control simulation for the present climate with constant 1950 atmospheric composition, and the other is a transient experiment with observed GHGs from 1950 to 1990 and 0.5% annual compounded increases of CO2 after 1990. Relative to the control, the last 50-year period of the GHG experiment indicates that the amplitude of the annual cycle of surface heat flux increases (i.e., increased flux into the ocean in summer and increased flux out in winter). The winter Arctic surface temperature increases at a faster rate than the global average, consistent with previous studies. The ice-albedo feedback mechanism accounts for some of this increase, but other feedbacks also contribute to the enhanced warming. To sort out some of these feedbacks, several additional model simulations are used to examine the relationships among sea-ice cover, sea-ice thickness, cloud cover, ocean circulation, surface temperature, and the surface energy budget. These simulations are then used to assess the role of the different feedbacks in the 150-year transient simulation and are compared with results from other models.