Intensified annual cycle of tropical Atlantic sea surface temperature regulates Pacific cooling

Despite the rapid warming in other oceans under increased anthropogenic radiative forcing, the eastern tropical Pacific has experienced a robust cooling trend over the recent decades since early 1980’s, which has exerted significant and prolonged impacts on global climate, partly mitigating the global warming and even inducing an intermittent hiatus trend in early 2000’s. This counterintuitive multidecadal cooling in the eastern tropical Pacific has perplexed the climate community regarding its underlying causes.

Many previous studies have proposed different potential explanations and/or hypotheses, including the influence of internal climate variability (e.g., the negative phase of interdecadal Pacific Oscillation), the inter-basin influence from the strong warming in the tropical Indian Ocean and Atlantic Ocean, the influence of aerosol forcing change, and the impact of Atlantic Multidecadal Variation (AMV), and so on.

In this study, we identify a distinct and previously underappreciated driver. By conducting a series of sensitivity coupled model experiments based on CESM2, we demonstrate that an intensified annual cycle of sea surface temperature in the tropical Atlantic can also drive a cooling in the eastern tropical Pacific over the past decades. The intensified annual cycle significantly alters the distribution of seasonal precipitation, leading to a net reduction of annual mean precipitation in the equatorial Atlantic. This dry state is accompanied by lower-troposphere divergence, inducing surface easterly anomalies along the equatorial Pacific and ultimately leading to a strong Pacific cooling. Our findings unveil a previously overlooked role of the tropical Atlantic annual cycle change in regulating tropical Pacific climate and shaping large-scale climate patterns.