Toward Advanced Modeling and Prediction of Arctic Sea Ice and Climate

Recent changes in the Arctic sea ice cover are one of the best examples of warming climate and its polar amplification. However, the causes and rate of sea ice melt are not yet fully understood. General circulation models (GCMs) vary significantly with their predictions of warming and the rate of sea ice melt in the Arctic Ocean, suggesting it may take from a few decades to centuries to melt most the sea ice cover in summer. The multi-model average forecast based on results from the Intergovernmental Panel for Climate Change Fourth Assessment Report (IPCC-AR4) suggest a 50% reduction of summer sea ice in the Arctic Ocean by the end of this century. Unfortunately the majority of those models have significant limitations in their representation of past and present variability in the Arctic. Some of these limitations include: northward oceanic heat convergence, distribution and variability of sea ice cover, and its export into the North Atlantic. The inability of climate models to reproduce the recent warming and ice melt in the Arctic Ocean diminishes their accuracy of future climate predictions. Satellite observations of ice extent and area imply a much faster rate of melting ice compared to GCM predictions, which may result in a summertime ice-free Arctic Ocean sometime before 2050. Yet, when ice thickness and volume are taken into account the rate of decline of Arctic sea ice might be even faster. To address some of these issues we analyze trends of sea ice decline based on the output from a regional ice-ocean model of the pan-Arctic region forced with realistic atmospheric data in comparison with trends estimated from observations. Under-ice ablation by anomalously warm water due to increased solar insulation and advection from the adjacent shelves is found to explain a significant portion of the total variance of sea ice thickness in the western Arctic Ocean. We hypothesize that the excess oceanic heat, that in recent years has accumulated below the surface during summer, is a critical initial factor in reducing ice concentration and thickness in the western Arctic Ocean at the early melting season and onwards the following year. Our findings imply that estimates of the rate of ice melt based on satellite aerial observations might be too conservative as well. The rates of sea ice thickness and volume melt estimated from our model results and recent data suggest much faster declining trend. This trend is robust and lends credence to the postulation that the Arctic not only might, but is likely to be ice-free during the summer in the near future.