Statistically downscaled CMIP6 ocean variables for European waters

Abstract

Abstract Climate change impact studies need climate projections at scales relevant to planning and management and to be available across a range of climate scenarios. To address current gaps, we statistically downscaled (SD) 4–7 CMIP6 models for four key indicators of marine habitat conditions: temperature, salinity, oxygen, and chlorophyll across European waters for three climate scenarios SSP1-2.6, SSP2-4.5, and SSP5-8.5. The results provided ensemble averages and uncertainty estimates to serve as input data for projecting the potential success of a range of Nature-based Solutions, including the restoration of habitat-forming species like seagrass in the Mediterranean and kelp in coastal areas of Portugal and Norway. Validation of the ensemble with observations of four European regions (North Sea, Baltic Sea, Bay of Biscay, and Mediterranean Sea) indicated that the SD projections realistically captured the climatological conditions of the historical period 1993–2020. Model skill (Liu-Mean Efficiency, Pearson correlation) clearly improved for both surface temperature and oxygen across all regions with a higher skill for temperature than oxygen with a difference of 0.2–0.4 points. Warming was evident across all areas and large differences among scenarios fully emerged from the background uncertainties related to internal variability and model differences in the second half of the century. Scenario-specific differences in acidification significantly emerged from model uncertainty and internal variability leading to distinct trajectories in surface pH starting from before mid-century (e.g., present day). Deoxygenation is present across all domains, but the signal was significantly weaker compared to the other two pressures when compared to model uncertainty and internal variability. The impact of different greenhouse gas trajectories was also less distinct. There was substantial regional to local heterogeneity in these quantitively characteristics underscoring the importance of highly spatially resolved physical and biogeochemical projections to address how climate change may impact marine ecosystems.