The left column shows the relevant processes in the pre-industrial climate and the right column shows how these same processes initially respond to GHG warming (this schematic does not show the final state). Technical Details(left panel): Convection is strongest in the western Pacific where the SST is the highest. Latent heating warms aloft, and evaporation cools the ocean surface. In the eastern Pacific, the thermocline is closest to the surface. Right panel: Under GHG warming, a uniform surface heat flux into the Pacific Ocean causes the SST to rise, but in the eastern tropical Pacific, the upwelling of cold water counters the forced warming. As a result, the zonal SST gradient increases. Schematic by climate.gov.