Heating the land cools the eastern and equatorial Pacific.

Günther, Moritz; Kang, Sarah M; Kaspi, Yohai · Sci Adv · 2026

basic_science · Level V

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Abstract

The unresolved recent multidecadal cooling of the eastern Pacific and its uncertain future remain key puzzles in climate dynamics. We propose the land-sea heating contrast as a potential driver of this phenomenon. To test this, we amplify the land-sea contrast by quadrupling carbon dioxide (CO<sub>2</sub>) only over land in a global coupled climate model. We show that this causes a pronounced transient cooling of the eastern and equatorial Pacific. A transient 1%-per-year CO<sub>2</sub> increase over land produces decadal cooling, suggesting relevance to the observed eastern Pacific cooling. Targeted simulations with locally increased CO<sub>2</sub> concentrations over different land regions reveal three drivers of this cooling: a northward intertropical convergence zone shift, a westward convection shift over the western Pacific, and strengthened subtropical highs from Rossby waves. These insights recast the commonly used ocean dynamical thermostat mechanism as a feedback rather than a driver of transient cooling and contribute to understanding and predicting Pacific temperature patterns.