Climatologists have identified that the Southern Ocean is relatively slow to respond to atmospheric warming. The lag effect is characterised by a temperature gradient between the tropics and the higher southern latitudes. Because of this, patterns of climate change in the Southern Hemisphere will continue to vary, and may even change direction, after greenhouse gas concentrations stabilise. Researchers are also using computer models to predict the behaviour of future El Nino-Southern Oscillation (ENSO) - the driver of El Nino and La Nina events - under an enhanced greenhouse regime.