Abstract
The likelihood of an El Niño breaking the annual global mean surface temperature (GMST) record during the 21st century is derived from 38 climate models from the Fifth Coupled Model Intercomparison Project (CMIP5). We find that, under a low emission scenario, one out of three El Niño events break the GMST record. The probability significantly increases to four out of five in a high emission scenario. About half of strong El Niños, but only one-fifth of weak El Niños, can set new GMST records in a low emission scenario. By contrast, even weak El Niños break the GMST record more regularly (68 ± 8% chance) in a high emission scenario. Both a stronger El Niño and a higher emission scenario induce a higher record-breaking GMST with a magnitude range from 0.03°C to 0.21°C above the previous record. El Niño accounts for more than half of record-breaking GMST occurrences in all emission scenarios. A comparison between CMIP3, CMIP5, and CMIP6 suggests that the analyses are not affected by model generations.
Highlights
The efficiency and rapidity of El Niño in pushing up the record warm global mean surface temperature (GMST) have been demonstrated in recent decades, notably during the strong 1997/98 and 2015/16 El Niños
As a naturally-occurring phenomenon, an El Niño can cause a strong and transient warmth of the global climate, superimposed on the gradual and persistent warming induced by greenhouse gas (GHG) forcing (Newell and Weare 1976, Pan and Oort 1983, Timmermann et al 1999, Trenberth 2002)
By removing the three models that simulate less than 14 El Niño events in Representative Concentration Pathways (RCP), the statistics shown in this study change by less than 5% and are still within the error bars of the ensemble mean estimates
Summary
The efficiency and rapidity of El Niño in pushing up the record warm global mean surface temperature (GMST) have been demonstrated in recent decades, notably during the strong 1997/98 and 2015/16 El Niños. When an El Niño occurs during the 21st century, an important question for near-term climate change prediction would be: how likely is the El Niño to break the GMST record, and by how much? It should be noted that we do not attempt to make actual and real-time predictions for particular events, but rather to obtain the statistics from the CMIP5 models about El Niño, global warming, and record-breaking GMST. We evaluate these statistics for each model before calculating their multi-model ensemble mean
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