Effects of climate change on extreme wave heights in the Atlantic Ocean using a CMIP5 multimodel ensemble : Under the high-emission scenario RCP8.5

Climate change driven variations of extreme wave heights can have considerable impacts on human activities developed onshore and offshore, as well as for the integrity of coastal ecosystems. Standard practice suggests to study those variations using ensembles of GCM forced dynamical wave simulations (wave simulations obtained from dynamically forcing a wave model with surface winds taken from global climate models). However, to date, there is very limited information on projections of extreme wave heights towards the end of the twenty-first century using this approach. A significant step is taken in this research by estimating 100-years return values of significant wave height in the whole Atlantic Ocean for the time slice 2081-2099 under the high-emission scenario RCP8.5, using a multi-model ensemble of CMIP5 GCM forced dynamical wave simulations, which is also validated against historical wave data from the wave hindcast CFSR. Results show a strong tendency of increasing extreme wave heights in 72% of the Atlantic Ocean domain with average rates of ~6.1%. The larger increases are observed in areas located north-west of the Norwegian coasts (strongest climate signal), south-east of Azores, south-east of Uruguay and in the north-east Atlantic. In contrast, the greater decreases are noticed east of Brazil, north-east of United States of America and in mid-latitudes of the North Atlantic. Furthermore, the findings of this study indicate that effects of climate change on extreme wave conditions are highly dependent on the latitude and the climate drivers: the atmospheric pressure gradients and the changes in size and frequency of extreme events