Uncertainty of ENSO-amplitude projections in CMIP5 and CMIP6 models

Abstract There is a long-standing debate on how the El Niño/Southern Oscillation (ENSO) amplitude may change during twenty-first century in response to global warming. Here we identify sources of uncertainty ENSO projections models participating Coupled Model Intercomparison Phase 5 (CMIP5) and 6 (CMIP6), quantify scenario uncertainty, model due internal variability. The exhibit large spread, ranging from increasing standard deviation up 0.6 °C diminishing − 0.4 by end century. ensemble-mean close zero. Internal variability main contributor first three decades; dominates thereafter, while relatively small throughout total increases CMIP5 CMIP6: reduced, considerably increased. with “realistic” dynamics have been analyzed separately categorized into too small, moderate comparison instrumental observations. smallest uncertainties are observed sub-ensemble exhibiting realistic amplitude. However, warming signal ENSO-amplitude undetectable all sub-ensembles. zonal wind-SST feedback identified as an important factor determining change: strength highly correlated across CMIP6 models.