Heating the land cools the eastern and equatorial Pacific.

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 (CO2) 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 CO2 increase over land produces decadal cooling, suggesting relevance to the observed eastern Pacific cooling. Targeted simulations with locally increased CO2 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.