The Effect of Strong Volcanic Eruptions on ENSO

The response of the El Niño–Southern Oscillation (ENSO) to tropical and extratropical volcanic eruptions has important worldwide implications for volcanically driven risk estimates. While there have been many studies on this subject using observations, paleoclimate archives, and model simulations, a comprehensive review of ENSO response to tropical and extratropical volcanic eruptions has not been presented to date. The relatively short observational record is suggestive of a relationship between tropical volcanism and El Niño events. Analyzing 17 previously defined reconstructions of ENSO, which on average span the past 550 years, we find that 70% of these reconstructions display a significant eastern Pacific warming (El Niño–like) response in the year of eruption, when a consistent set of volcanic events dates are used. There also appears to be an emerging consensus from models, with the overwhelming majority displaying a relative El Niño–like response in the eruption year. Thus, here we report that there is a clear consistency of evidence between observations, paleo-proxies, and models. Questions remain, however, over exactly how the near‐uniform radiative cooling of a tropical volcanic event projects onto ENSO. There is little observational and paleoclimatic evidence for the impact of extratropical volcanism on ENSO; however, models suggest that an extratropical Northern (Southern) Hemisphere eruption leads to a relative El Niño–like (La Niña–like) response. Despite the consistency in the evidence presented above, many subtle differences still exist among the modeled response to tropical and extratropical volcanic forcing that could be aided by the use of a consistent experimental protocol for general circulation model simulations (i.e., VolMIP).