Human-Forced Changes to ENSO-Driven Rainfall Anomalies

The El Nino–Southern Oscillation (ENSO) drives substantial variability in rainfall, severe weather, flooding and associated death tolls, agricultural production, ecosystems, and disease in many parts of the world. Given that further human-forced changes in the Earth’s climate system seem inevitable, the possibility exists that the character of ENSO and its impacts will change over the coming century. Here we use results from CMIP5 climate models and AGCM experiments to examine anthropogenic changes in ENSO-driven rainfall anomalies over the Pacific Ocean. We will examine changes in both the frequency and intensity of both El Niño and La Niña events, including the most disruptive of these events, as well as changes to the spatial structure of ENSO-driven rainfall anomalies. We will identify a range of robust changes, and we will explain the main reasons for the changes identified. The extent to which recent international agreements on reducing greenhouse gas emissions can limit the projected changes will be discussed.