Regional scaling of sea surface temperature with global warming levels in the CMIP6 ensemble

Abstract Sea surface temperature (SST) and sea surface air temperature (SSAT) are commonly used as proxies for investigating the impact of climate change on oceans. These variables have been warming since pre-industrial times and are expected to continue to warm in the future under all Shared Socioeconomic Pathways (SSPs). However, they are warming at different rates in a spatially heterogeneous way, even with some cooling spots. In this work, we provide a general overview on the regional scaling of SST and SSAT with global warming, based on a 26-member CMIP6 ensemble. We use global warming level (GWL) as a climate change dimension, and analyze the slope of the linear fit (β) between decadal sea temperature anomalies and the corresponding GWLs during the 21st century. This analysis is done globally, regionally, and also grid-point by grid-point. The results show that SST and SSAT scale linearly with GWL at global scale, with scaling factors 0.71±0.001 K/K and 0.86±0.001 K/K, respectively. These results are quite robust, with small differences between seasons, SSPs and horizontal model resolutions. However, large differences appear at regional scale, and the scaling of the two temperatures are strongly affected by sea-ice. The lowest values are obtained for the Southern Ocean region, β = 0.54±0.005 K/K, projecting the mean SST to increase half as fast as the global mean temperature. These results provide relevant information for a refinement of ocean reference regions, taking into account the spatial homogeneity in terms of regional response to global warming.