Global dynamical projections of surface ocean wave climate for a future high greenhouse gas emission scenario

A global 1° implementation of the spectral wave model, WaveWatch III, was forced with surface winds from two atmosphere-ocean general circulation models (AOGCMs: ECHAM5 and CSIRO Mk3.5), dynamically downscaled to 60 km using the Cubic Conformal Atmospheric Model. Two 30-yr time slices were simulated: 1979-2009 representing current climate, and 2070-2099 representing a future climate scenario under a high greenhouse gas emission scenario (SRES A2). A further wave model simulation with forcing from the NCEP Climate Forecast System Reanalysis for 1979-2009, using the same model settings as the climate model forced runs, serves as a benchmark hindcast to assess skill of climate-model-derived wave fields. Climate model forced wave simulations for the 1979-2009 time-slice display biases relative to the benchmark wave climate - notably an overestimation of wave generation in the Southern Ocean, which influences broad regions of the Pacific which receive these waves as swell. Wave model runs were repeated following bias-adjustment of the climate model forcing winds with the aim to reduce biases, but model skill to simulate the monthly 99th percentile of significant wave heights deteriorates severely.Projected future changes in wave climate (between 1979-2009 and 2070-2099) under the SRES A2 greenhouse gas emission scenario are relatively insensitive to whether bias-adjustment of winds has been applied. Two robust features of projected change are observed from the two climate model sets which are qualitatively consistent with previous studies: a projected increase of Southern Ocean wave generation leading to approximately 10% increase in Southern Ocean mean significant wave heights (HSm), and a projected decrease in wave generation in the North Atlantic, with changes in HSm of similar magnitude.Interannual anomalies of monthly mean significant wave height, HSm, were regressed against climate indices (Southern Oscillation Index - SOI; North Atlantic Oscillation - NAO and the Southern Annular Mode - SAM) over each time-slice. Significant differences in the relationships between wave height variability and these climate indices between current and projected climates are observed. For example, a significant shift from negative to positive correlation between the NAO and HSm anomalies along the western European and north-west African coasts in the projected future climate is noted. The potential future changes in wind-wave characteristics, and the changing relationships between interannual variability of wave climate with identified climate indices, as a response to projected future climate scenarios have broad implications for a range of processes and activities in the coastal, near-and-off-shore environments.