ENSO—Past, Present, and Future

ENSO events in the past two decades stand out against the background of the 100+ years of instrumental data that provides our primary knowledge of these phenomena. This brings immediacy to the obvious question of how ENSO might change under the impact of anthropogenic influences on the climate system. It is a socially relevant question, in that societies seemingly can withstand a gradual change in climate more easily than unexpected cycles of drought and flood and other changes in variability. What is known about ENSO's future prospects will be reviewed, and disparate interpretations of the last decades of the 20th century will be considered. Both topics demand a consideration of ENSO variability in a longer sweep than 100 years. What paleoproxy data and modeling suggest about the variations of the ENSO cycle through the Holocene will be brought into the discussion.