Observed and Simulated Fingerprints of Multidecadal Climate Variability and Their Contributions to Periods of Global SST Stagnation

This study investigates spatiotemporal features of multidecadal climate variability using observations and climate model simulation. Aside from a long-term warming trend, observational SST and atmospheric circulation records are dominated by an almost 65-yr variability component. Although its center of action is over the North Atlantic, it manifests also over the Pacific and Indian Oceans, suggesting a tropical interbasin teleconnection maintained through an atmospheric bridge. An analysis shows that simulated internal climate variability in a coupled climate model (CSIRO Mk3.6.0) reproduces the main spatiotemporal features of the observed component. Model-based multidecadal variability includes a coupled ocean-atmosphere teleconnection, established through a zonally oriented atmospheric overturning circulation between the tropical North Atlantic and eastern tropical Pacific. During the warm SST phase in the North Atlantic, increasing SSTs over the tropical North Atlantic strengthen locally ascending air motion and intensify subsidence and low-level divergence in the eastern tropical Pacific. This corresponds with a strengthening of trade winds and cooling in the tropical central Pacific. The model's derived component substantially shapes its global climate variability and is tightly linked to multidecadal variability of the Atlantic meridional overturning circulation (AMOC). This suggests potential predictive utility and underscores the importance of correctly representing North Atlantic variability in simulations of global and regional climate. If the observations-based component of variability originates from internal climate processes, as found in the model, the recently observed (1970s-2000s) North Atlantic warming and eastern tropical Pacific cooling might presage an ongoing transition to a cold North Atlantic phase with possible implications for near-term global temperature evolution.