Mapping the future expansion of Arctic open water

Sea ice impacts most of the Arctic environment, from ocean circulation and marine ecosystems to animal migration and marine transportation. Sea ice has thinned and decreased in age over the observational record(1,2). Ice extent has decreased(3). Reduced ice cover has warmed the surface ocean(4), accelerated coastal erosion(5,6) and impacted biological productivity(7). Declines in Arctic sea-ice extent cannot be explained by internal climate variability alone and can be attributed to anthropogenic effects(8,9). However, extent is a poor measure of ice decline at specific locations as it integrates over the entire Arctic basin and thus contains no spatial information. The open water season, in contrast, is a metric that represents the duration of open water over a year at an individual location(10,11). Here we present maps of the open water season over the period 1920-2100 using daily output from a 30-member initial-condition ensemble of business-as-usual climate simulations(12) that characterize the expansion of Arctic open water, determine when the open water season will move away from pre-industrial conditions ('shift' time) and identify when human forcing will take the Arctic sea-ice system outside its normal bounds ('emergence' time). The majority of the Arctic nearshore regions began shifting in 1990 and will begin leaving the range of internal variability in 2040. Models suggest that ice will cover coastal regions for only half of the year by 2070.