The tropical Pacific sea-surface temperature gradient—the contrast between warm western Pacific waters and cooler eastern Pacific waters—helps drive global rainfall patterns and influences climate sensitivity. Climate models have generally predicted that this gradient would weaken as the planet warms, yet observations show the opposite: a strengthening gradient with cooling in the eastern tropical Pacific.
In a new modeling study published in AGU Advances, researchers ran simulations with an abrupt quadrupling of atmospheric CO2 and found a two-phase response. The equatorial Pacific gradient first strengthens, driven by ocean circulation changes near the equator and atmospheric feedbacks from the Northern Hemisphere. Over longer timescales, slow ocean adjustments take over and the gradient weakens, eventually matching the model-projected pattern.
These results help explain why short-term observations and long-term model projections seem to disagree. By identifying the mechanisms behind the initial strengthening, the study offers a clearer picture of how the Pacific responds to greenhouse forcing and could improve the accuracy of future climate projections.