Ocean dynamical thermostat is a physical mechanism through which changes in the mean radiative forcing influence the gradients of sea surface temperatures in the Pacific Ocean and the strength of the Walker circulation. Increased radiative forcing (warming) is more effective in the western Pacific than in the eastern where the upwelling of cold water masses damps the temperature change. This increases the east-west temperature gradient and strengthens the Walker circulation. Decreased radiative forcing (cooling) has the opposite effect.
The process has been invoked to explain variations in the Pacific Ocean temperature gradients that correlate to insolation and climate variations. It may also be responsible for the hypothesized correlation between El Niño events and volcanic eruptions, and for changes in the temperature gradients that occurred during the 20th century. Whether the ocean dynamical thermostat controls the response of the Pacific Ocean to anthropogenic global warming is unclear, as there are competing processes at play; potentially, it could drive a La Niña-like climate tendency during initial warming before it is overridden by other processes.