Global warming will increase the variability of the eastern Pacific El Nino, reports a paper in this week’s Nature. This increase could result in more frequent extreme weather events in the future.

The El Nino-Southern Oscillation (ENSO) is the most influential climate variation on Earth; the eastern Pacific El Nino is linked to flooding in eastern Pacific regions and droughts in western Pacific regions. However, a lack of inter-model consensus regarding the response of eastern Pacific sea surface temperatures - a crucial diagnostic for the eastern Pacific El Nino - means that the effect of global warming on the ENSO remains uncertain. In addition, most previous work has assessed changes in specific geographic regions, with inconclusive results.

Wenju Cai and colleagues studied 17 climate models from the Coupled Model Intercomparison Project Phase 5 (CMIP5) to assess changes in the eastern Pacific El Nino under future global warming. By tracking the anomaly centre of each model (the location of the most extreme temperature change), the authors report that almost all models (88%) predict an increase in sea surface temperature variability at their respective anomaly centre. This corresponds to an overall mean increase of 15% in eastern Pacific El Nino sea surface temperatures variability between present-day (1900-1999) and predicted future (2000-2099) climates.

Such an increase in sea surface temperature variance implies an increase in the number of ‘strong’ eastern Pacific El Nino events (corresponding to large sea surface temperature anomalies), and the authors conclude that we should expect more extreme weather events in the future as a result.