El Niño and the Southern Oscillation (ENSO) have profound effects on South American climate. Warm ENSO events (El Niños) and cold ENSO events (La Niñas), which occur on year-to-year time scales, are associated with droughts, floods, and other extreme weather events across the continent. Anthropogenic greenhouse gas warming of the planet will also likely have a profound effect on South America, through both gradual shifts in the baseline climate and increases in extreme events, including possible changes in the ENSO cycle.
There are indications that climate change may already be having an impact in South America, with temperature trends observed in the Galápagos and in the altiplano of the northern Andes and in the shrinking of tropical mountain glaciers. There has also been a shift in the behavior of El Niño, with an increased tendency for warm sea surface temperature anomalies to be concentrated in the central Pacific rather than in the eastern Pacific during the past 2 decades. These central Pacific (or “Modoki,” which means “similar but different” in Japanese) El Niños have a different signature than eastern Pacific El Niños in terms of teleconnection patterns on weather variability in South America and in terms of effects on marine ecosystems and fisheries along the west coast of the continent. However, the instrumental climate record is relatively short, and many of the observed trends could simply be the result of natural decadal climate variability that is unresolved in observations.