Global warming will probably change the balance of the physical processes that determine the strength and frequency of El Nino and La Nina events, reports a review online this week in Nature Geoscience. Because amplifying and dampening effects are both expected to be affected, it is not yet possible to predict the overall evolution of this Pacific climate 'see-saw' in a warming world.

Mat Collins and co-authors reviewed projected changes in the tropical Pacific climate over the next century. They found that the effect of climate warming on individual components of the ocean-atmosphere system, such as the strength of upwelling in the eastern tropical Pacific, and the temperature of the sea surface and its interplay with that of the air is well understood. But not all of the expected changes will affect El Nino characteristics in the same way. The authors conclude that the climate variability associated with El Nino and La Nina events could intensify, weaken or even undergo little change depending on the balance of changes in the underlying processes.