An ensemble of regional CMIP3/CMIP5 wind wave scenarios for the North Sea and the Baltic Sea: a revisit

Abstract. Storms and associated marine hazards pose a environmental risks, particularly under long-term changes driven by anthropogenic climate change. This study assesses the potential impacts of future climate change on annual median and extreme wave conditions in the North Sea and the Baltic Sea using a ensemble of up to 14 and 8 regional projections, respectively. The ensemble includes simulations based on IPCC CMIP3 and CMIP5 scenarios, incorporating a range of global and regional climate models, initial conditions, and emission scenarios to reflect diverse sources of uncertainty. High- and low-emission sub-ensembles were used to evaluate the influence of emission scenarios on projected wave climate changes towards the end of the 21st century. Despite variations in magnitude and spatial patterns across the ensemble, some robust spatial and temporal trends emerge. A meridional gradient of changes is simulated in the North Sea. Significant wave heights decrease along the western margins and increase in the east. These changes are more pronounced under high-emission scenarios, with median values decreasing by up to 5 % in the west and annual maxima increasing by over 5 % in the east. Time series analysis confirms these trends at selected locations, although there is still considerable internal variability among ensemble members. In the Baltic Sea, both median and extreme wave heights are simulated to increase by more than 5 % in some areas. Although the response to emission scenarios is less distinct than in the North Sea, high-emission scenarios still yield more pronounced increases. Temporal analysis reveals that simulated changes become statistically significant by mid-century in central areas and later in western regions. The results indicate a robust increase in wave height in the eastern North Sea and many regions of the Baltic Sea, as well as a consistent decrease in the western North Sea, particularly under high-emission scenarios. However, these trends are superimposed on substantial temporal and internal variability, highlighting the importance of using ensemble-based assessments to evaluate future marine climate conditions.