Sea Ice Retreat Contributes to Projected Increases in Extreme Arctic Ocean Surface Waves

The projected changes and trends in the regional annual and monthly maxima of the significant wave height (H-s) in the Arctic Ocean are studied using wave simulations derived from the CMIP5 (Coupled Model Intercomparison Project Phase 5) climate simulations for 1979-2005 and 2081-2100 periods. Under the RCP8.5 scenario, the regional annual maximal H-s increases on average up to similar to 3 cm/year, or >0.5%/year, relative to the 1986-2005 climatological value, in many Arctic areas (and up to 0.8%/year in the east side of the Arctic Ocean). While strong winds need to occur for large waves to develop, the changes in wind speed alone cannot explain the increases in the regional maximal H-s. Sea ice retreat also plays an important role by increasing fetch to promote wave growth, thereby contributing notably to the projected increase in wave height. It also contributes to increasing the probability of strong winds over the widening ice-free waters. Plain Language Summary Significant wave height (H-s) is the average of the highest third of wave heights. Using simulations of historical and future wave climates, we reveal that, under the RCP8.5 scenario, regional annual maximal H-s in the Arctic Ocean and surrounding seas is projected to increase at a rate of up to similar to 3 cm/year, or equivalently up to 80%, relative to the 1986-2005 climate period, over a 100-year period. While strong winds need to occur for large waves to develop, changes in wind speed alone cannot explain the increases in wave height. Sea ice retreat also plays an important role by increasing the water distance over which wind can blow, thereby promoting wave growth and thus contributing to the increase in wave height. There is also an increase in the probability of strong winds over the widening ice-free waters due to sea ice retreat.