Increase in ENSO Frequency and Intensity Under 20th and 21st Century Warming: Insights From CMIP6 Large Ensembles

Abstract Future changes in El Niño‐Southern Oscillation (ENSO), the dominant mode of global climate variability, remain uncertain. Accordingly, large ensembles—which allow internally‐generated variations to be averaged out—are essential for assessing the response of ENSO to external forcing. In this study, we analyze state‐of‐the‐art large‐ensemble simulations from CMIP6 climate models and show that, in most models, ENSO frequency increases under anthropogenic warming. Two factors drive this frequency increase. First, a shift toward the Eastern Pacific (EP) El Niño pattern—characterized by higher frequencies and greater amplitudes relative to the Central Pacific (CP) pattern. Second, an overall increase in the frequency of both EP and CP variability. These changes scale with the intensity of anthropogenic forcing. Most models also exhibit ENSO strengthening that begins in the century and continues throughout the century. Consequently, the observed intensification of ENSO during the second half of the century could be of anthropogenic origin.