The impact of global warming on the tropical Pacific Ocean and El Niño

Anthropogenic climate change is now well established as a global issue of scienti!c and political importance. One of the principal impacts of the gradual change associated with anthropogenic climate warming comes from a shi" in, or an exaggeration of, pre-existing natural variability. For example, if the average distribution of precipitation shi"s to higher or lower values, this can mean that thresholds to #ooding or drought are crossed more o"en. One of the most important sources of natural climatic variability is ENSO. On a timescale of two to seven years, the eastern equatorial Paci!c climate varies between anomalously cold (La Niña) and warm (El Niño) conditions. $ese swings in temperature are accompanied by changes in the structure of the subsurface ocean; variability in the strength of the equatorial easterly trade winds; shi"s in the position of atmospheric convection; and global teleconnection patterns associated with these changes that lead to variations in rainfall and weather patterns in many parts of the world. In the simplest possible scenario, present-day weather and climate variability such as ENSO would continue as before, superimposed onto a gradual mean warming of the global background climate. However, it is not clear whether the climate system will evolve in such a simple manner. As the mean state of both the atmosphere and the ocean in the tropical Paci!c region evolve, the amplitude, frequency, seasonal timing or spatial patterns of ENSO could be altered1. Furthermore, the way ENSO a%ects remote The impact of global warming on the tropical Pacific Ocean and El Niño