ENSO amplitude uncertainty under global warming in CMIP5 models
<p>The possible change of ENSO amplitude during the 21<sup>st</sup> century in response to global warming has been analyzed in models participating in the Coupled Model Intercomparison Phase 5 (CMIP5). Three types of uncertainties are investigated: scenario uncertainty, model uncertainty, and uncertainty due to internal variability.</p><p>The ENSO response obtained from the CMIP5 models is highly uncertain, leading to an ensemble-mean amplitude change of close to zero until the end of the 21<sup>st</sup> century, with an uncertainty exceeding 0.3 &#176;C. The internal variability is the main contributor to the uncertainty during the first two decades of the projections. The inter-model differences dominate thereafter, while scenario uncertainty is relatively small throughout the whole 21<sup>st</sup> century. The zonal wind-SST feedback has been identified as an important factor of ENSO amplitude change: the global warming signal in the ENSO amplitude and zonal wind-SST feedback are highly correlated across the CMIP5 models, with correlation coefficients of 0.87, 0.84 and 0.78 for the RCP4.5, RCP6.0 and RCP8.5 scenarios, respectively.</p><p>The CMIP5 models with realistic ENSO dynamics have been analyzed separately. In this sub-ensemble, the global warming signal is strengthened with a mean ENSO amplitude decrease of approximately 0.1&#176;C by the end of the 21<sup>st</sup> century. When only considering models with large decadal ENSO amplitude variability, the decrease in ENSO amplitude amounts to 0.1&#176;C and 0.2&#176;C for the RCP4.5 and RCP8.5 scenarios, respectively.</p>