Advancements and Limitations in Understanding and Predicting Arctic Climate Change

Recent reductions of the arctic sea ice cover since the late 1990s provide one of the top examples of warming climate. However, the causes of ice melt and its rate are not fully understood. When compared with the satellite record of summer sea ice extent, simulations from general circulation models (GCMs) participating in the Intergovernmental Panel for Climate Change Fourth Assessment Report are too conservative in their representation of ice melt in the Arctic Ocean. In addition, ice thickness and volume estimates from submarines and satellites as well as from some models suggest that the trend of arctic ice extent decline may not reflect the more rapid rate of ice volume melt. The inability of climate models to reproduce the recent warming and ice melt in the Arctic diminishes their accuracy of future climate predictions.

A more realistic regional model representation of the Arctic Ocean and its sea ice indicates an accelerated thinning trend during the last decade. The model skill is evaluated against ice thickness data gathered during the last three decades. It appears that removal of ice from the shelves in the western Arctic for prolonged time acts to increase oceanic heat content in the upper ocean year around, which in turn has a significant impact on sea ice cover. Warm water advection from the adjacent shelves exerts a thermodynamic forcing of sea ice through the under-ice ablation and the lateral melt downstream at marginal ice zones. However, the absolute magnitude and long term variability of the upper ocean heat storage and fluxes are not well known from observations and are typically poorly represented in models. We hypothesize that the excess oceanic heat that has accumulated during recent summers due to increased solar insulation and oceanic heat convergence is a critical initial factor in reducing ice concentration and thickness in the western Arctic Ocean before the melt season and onwards the following year. The modeled thinning trend is robust which lends credence to the postulation that the Arctic not only might, but is likely to be almost ice-free during the summer in the near future.

This talk will synthesize and critically assess various predictions / projections of arctic sea ice melt. We will outline some possible improvements and in particular the need for high spatial resolution data and model results on sea ice thickness, oceanic heat fluxes, and air-sea interactions to improve understanding and predictive skills of GCMs.