Projected Impact of Climate Change on the Energy Budget of the Arctic Ocean by a Global Climate Model

Abstract

The annual energy budget of the Arctic Ocean is characterized by a net heat loss at the air?sea interface that is balanced by oceanic heat transport into the Arctic. Two 150-yr simulations (1950?2099) of a global climate model are used to examine how this balance 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. For the present climate the model agrees well with observations of radiative fluxes at the top of the atmosphere, atmospheric advective energy transport into the Arctic, and surface air temperature. It also simulates the seasonal cycle and summer increase of cloud cover and the seasonal cycle of sea ice cover. In addition, the changes in high-latitude surface air temperature and sea ice cover in the GHG experiment are consistent with observed changes during the last 40 years. Relative to the control, the last 50-yr period of the GHG experiment indicates that even though the net annual incident solar radiation at the surface decreases by 4.6 W m?2 (because of greater cloud cover and increased cloud optical depth), the absorbed solar radiation increases by 2.8 W m?2 (because of less sea ice). Increased cloud cover and warmer air also cause increased downward thermal radiation at the surface so that the net radiation into the ocean increases by 5.0 W m?2. The annual increase in radiation into the ocean, however, is compensated by larger increases in sensible and latent heat fluxes out of the ocean. Although the net energy loss from the ocean surface increases by 0.8 W m?2, this is less than the interannual variability, and the increase may not indicate a long-term trend. The seasonal cycle of heat fluxes is significantly enhanced. The downward surface heat flux increases in summer (maximum of 19 W m?2, or 23% in June) while the upward heat flux increases in winter (maximum of 16 W m?2, or 28% in November). The increased downward flux in summer is due to a combination of increases in absorbed solar and thermal radiation and smaller losses of sensible and latent heat. The increased heat loss in winter is due to increased sensible and latent heat fluxes, which in turn are due to reduced sea ice cover. On the other hand, the seasonal cycle of surface air temperature is damped, as there is a large increase in winter temperature but little change in summer. The changes that occur in the various quantities exhibit spatial variability, with the changes being generally larger in coastal areas and at the ice margins.