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The study described here is a synthesis of global climate model projections of Northern Hemisphere sea ice through the end of the 21st century. The synthesis includes an enhancement of the informational content of the projections from a set of five global atmosphere-ocean-ice models. The adjustments are based on the systematic errors in the models’ present-day simulations relative to the HadISST observational data set. All models show decreases of sea ice through the 21st century when forced by the B2 scenario of greenhouse gas and aerosol concentrations. However, the differences in the present-day ice coverage simulated by the models are sufficiently large that they dominate the across-model variances of the projected ice extents. The adjustments based on the present-day biases remove much of the spread among the projections. The decreases of the adjusted ice extent by the year 2100 range from about 12% to about 46%. The percentage decreases are larger in summer than in winter; much of the Arctic Ocean is ice-free at the time of the summer ice minimum by the year 2099.