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Abstract:
Herein global and regional spatial patterns of sea-level change in the altimeter record are compared to contemporaneous (1993-2014) patterns of change from state-of-the-art climate models. A multi-model ensemble of Coupled Model Intercomparison Project phase 6 (CMIP6) historical simulations are analyzed (n = 167) and a weak and largely zonally homogenous pattern of change is found in the ensemble mean. While some CMIP6 simulations have regional patterns of change that are a close match to the altimeter record, none are a good match globally (maximum centered pattern correlation statistic globally of 0.40 and 5-95% range of -0.20-0.26). Our focus in this study is on differences in patterns of change across the individual historical simulations and the role for internal variability, external forcing, and structural factors in driving these differences. For instance, a close linear relationship is found between the global and regional patterns of change in sea surface temperature (SST) and those in sea level, and both patterns can be related to the trajectories of common modes of atmosphere-ocean variability. Using a self-organizing maps-based approach we calculate the number of distinct patterns of change both globally and regionally across the historical simulations. The same analysis applied to pre-industrial control simulations (with no transient external forcing and from the same climate models) reveals the regions in which external forcing, principally anthropogenic in origin, has impacted the number and character of distinct patterns of change. Hotspots include the tropical Indian Ocean and the Pacific Ocean globally.
