Oceans and the atmosphere constantly interact with each other; surface winds drive the ocean currents, moving warm water polewards and cold water equatorwards, and evaporation from warm oceans removes latent heat from the atmosphere. This latent heat is released when the vapour condenses with height. See Smith et al. (2006) J. Climate 19, 18 for a low-resolution coupled ocean–atmosphere general circulation model, and Ciasto and Thompson (2008) J. Climate 21, 6 on the Southern Hemisphere. Ocean–atmosphere oscillations are interactions which switch suddenly from one phase to another; the best known being the El Niño–Southern Oscillation. See McCabe et al. (2004) Proc. Nat. Acad. Sci. 101 on ocean influences on drought.