Record-Breaking Temperature during El Niño

Trenberth [2002] has shown the importance of diabatic heating process from the tropical ocean (particularly over the Niño3.4 region) to the global mean surface temperatures (GMST). In addition, since 1980, 11 out of 14 record-breaking annual GMSTs have coincided with an El Niño event [Yin et al., 2017]. Therefore, it is natural for us to ask ” What is the chances of an El Niño event to break the global temperature during the 21st Century? and by how much?”

Currently, the gradual warming climate keeps shifting the probability distribution of GMST toward higher values. Once an internal variation, i.e. El Niño, happens, an record-breaking GMST could take place. In our study, we study if the strength of the background warming and strength of El Niño could affect the chance and magnitude of the record-breaking GMST during El Niño [Hsu and Yin, 2019]. We derive the chance and magnitude base on the multi-model ensemble statistics from the Fifth Coupled Model Intercomparison Project (CMIP5) during the 21st Century.

Based on our finding, the emission scenario has a significant influence on the likelihood of record-breaking GMST happened during El Niño, with stronger emission scenario causing higher likelihood. Under a low emission scenario (RCP2.6), one out of three El Niño events breaks the GMST record during the 21st century. The probability increases to four out of five in a high emission scenario (RCP8.5). The result shows the importance of climate change mitigation in reducing record-breaking GMST during important internal variability like El Niño. However, emission scenario has a limited influence on the likelihood of record-breaking GMST occurring during strong El Niño. A strong El Niño produces a GMST variation that is large enough to break the GMST record regardless of the background warming trend difference between RCP4.5 and RCP8.5. Stronger El Niño also induces higher record-breaking magnitude in each RCP. The magnitude can range from 0.03\(^\circ\)C to 0.21\(^\circ\)C based on individual CMIP5 models. El Niño accounts for more than half of record-breaking GMST occurrences in all warming scenarios which shows the importance role of El Niño in record-breaking GMST.