Robustness and uncertainties in global multivariate wind-wave climate projections

Understanding climate-driven impacts on the multivariate global wind-wave climate is paramount to effective offshore/coastal climate adaptation planning. However, the use of single-method ensembles and variations arising from different methodologies has resulted in unquantified uncertainty amongst existing global wave climate projections. Here, assessing the first coherent, community-driven, multi-method ensemble of global wave climate projections, we demonstrate widespread ocean regions with robust changes in annual mean significant wave height and mean wave period of 5-15% and shifts in mean wave direction of 5-15°, under a high-emission scenario. Approximately 50% of the world's coastline is at risk from wave climate change, with ~40% revealing robust changes in at least two variables. Furthermore, we find that uncertainty in current projections is dominated by climate model-driven uncertainty, and that single-method modelling studies are unable to capture up to ~50% of the total associated uncertainty.

This study represents Task 3 of the second phase of the Coordinated Ocean Wave Climate Project (COWCLIP) (https://cowclip.org/), an international collaborative working group endorsed by the Joint Technical Commission for Oceanography and Marine Meteorology (JCOMM) - a partnership between the World Meteorological Organization (WMO) and the Intergovernmental Oceanographic Commission of UNESCO (IOC-UNESCO). We acknowledge the different climate modelling groups, the Program for Climate Model Diagnosis and Intercomparison (PCMDI) and the World Climate Research Program’s (WCRP) Working Group on Coupled Modelling (WGCM). We acknowledge ECMWF for availability of ERA-Interim data, and Australia’s Integrated Marine Observing System (IMOS) for altimeter wind/wave data, used for model validation. J.M., M.H. and C.T. acknowledge the support of Australian Government National Environmental Science Program (NESP) Earth Systems and Climate Change Hub. B.T and M.W acknowledge the support of the Regional and Global Climate Modeling Program of the U.S. Department of Energy, Office of Science, Office of Biological and Environmental Research, through contract DE-AC02-05CH11231, and the National Energy Research Supercomputing Center (NERSC) of the Lawrence Berkeley National Laboratory. I.Y. acknowledges ongoing support from the Australian Research Council through grant DP160100738 and to Integrated Marine Observing System (IMOS). N.M, T.S, A.B and B.K. acknowledge the support of the TOUGOU Program by MEXT, Japan, JSPS-Kakenhi Program. L.E. acknowledges the support of the US Geological Survey Coastal and Marine Hazards/Resources Program. Ø.B and O.J.A acknowledge the support of the Research Council of Norway through the ExWaMar project through grant 256466. We thank all contributors to the COWCLIP project including, Christian Appendini (National Autonomous University of Mexico, Mexico), Fabrice Ardhuin (Ifremer, France), Nikolaus Groll (Helmholtz-Zentrum Geesthacht Zentrum, Germany), Sarah Gallagher (Met Éireann, Ireland), Sergey Gulev (Moscow State University, Russia) and Will Perrie (Bedford Institute of Oceanography, Canada).