A Review on the Sensitivity of ENSO to Strong Volcanic Eruptions

Understanding the influence of volcanic eruptions on ENSO variability and associated climatic impacts is of great scientific and social importance. Although, many studies on the volcano-ENSO nexus are available; however, a thorough review of ENSO response to tropical and extratropical volcanic eruptions is still missing. Therefore, this study aimed to provide a comprehensive review of the ENSO response to volcanism using the high-resolution Coupled Model. Past studies suggest that there is an emerging consensus in models, with the overwhelming majority showing a relative El Niño-like response during the eruption year. ENSO reconstructions spanning the past several centuries also display a significant eastern Pacific warming in the year of the eruption. We noticed that there is a clear consistency of evidence between observations, proxies, and single coupled model ensemble experiments. Model ensemble experiments with and without tropical volcanic forcing show that the post-eruption warming seen in higher latitudes is caused by concurrent positive ENSO phase that modulated the NAO circulation resulting in high-latitude winter warming over Eurasia and cooling in the Middle East and North Africa. Questions still remain, for instance, how exactly the nearly uniform radiative cooling by a tropical volcanic event projects onto ENSO. Moreover, there are fewer observational records for the impact of extratropical volcanism on ENSO. However, model-based studies suggest that an extratropical Northern (Southern) Hemispheric eruption leads to a relative El Niño (La Niña)-like response. Despite the consistency, many subtle differences still exist in the simulated response to tropical and extratropical volcanism that could be further improved by using a unified experimental setup in the general circulation modeling. Hence, adequate sampling is critical to accurately assess ENSO responses both in models and observations.