We know that the El Niño-Southern Oscillation (ENSO) is the main source of year to year temperature variability in the oceans and atmosphere. Through changes in winds and ocean currents it has the ability take up or release heat to the atmosphere. It doesn’t really change the long-term temperature but can make one year hotter (El Niño) or cooler (La Niña) than the next. ENSO occurs in the tropical Pacific but is strong enough to have a global influence.
We can take our climate model again but instead of assigning the whole ocean temperature we just put in a “fake” El-Niño/La-Niña. We make the tropical Pacific ocean temperatures go up and down - over a period of four years - and let the rest of the ocean, and the land, respond. The period of four years is related to the actual period ENSO, although the real world is much less regular than our model.
In this experiment, the global land surface temperature still responds with amplified variability relative to the ocean; if the ocean surface temperature increases or decreases by \(1^{\circ}\) the land temperature will increase or decrease by almost \(1.5^{\circ}\). Essentially, we can control the global land temperature by changing the temperature of the tropical Pacific ocean.