How Likely is an El Niño to Break Global Mean Surface Temperature Record during the 21st Century?

The likelihood of an El Nino to break the global mean surface temperature (GMST) record during the 21st century is derived from 38 climate models in Fifth Coupled Model Intercomparison Project (CMIP5). We find that, under a low emission scenario (RCP2.6), one out of three El Nino events breaks the GMST record. The probability significantly increases to four out of five in a high emission scenario (RCP8.5). About half of strong El Ninos, but only one-fifth of weak El Ninos, can set new GMST records in low emission scenario. By contrast, even weak El Ninos defined by Oceanic Nino Index (ONI) can break the GMST record more regularly (68%± 8% chance) in high emission scenario. Both stronger El Nino and higher emission scenario induce a higher record-breaking GMST with magnitude range from 0.03 degree Celcius to 0.21 degree Celcius above the previous record. El Nino accounts for more than half of record-breaking GMST occurrences in all emission scenarios. To further investigate, we separate the El Nino to two types (Central Pacific and Eastern Pacific) and perform the same statistical analysis. A comparison between CMIP3, CMIP5, and CMIP6 suggests that the analyses are not affected by model complexity. A regional analysis of the enthalpy budget is performed to better understand the mechanism behind the increasing GMST.