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 deliberately amplify the land-sea contrast by quadrupling CO ₂ 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 ₂ increase over land produces similar cooling on decadal time scales, suggesting relevance to the observed Eastern Pacific cooling. Targeted simulations with locally increased CO ₂ concentrations over different land regions reveal three drivers of this cooling: a northward ITCZ shift, a westward convection shift over the Western Pacific, and strengthened Subtropical Highs from Rossby waves. These insights question the commonly employed ocean dynamical thermostat mechanism's importance for transient cooling, and contribute to understanding and predicting Pacific temperature patterns.