OS021-05
No consistent ENSO response to volcanic forcing over the last millennium

Wednesday, 9 December 2020: 19:16
Virtual
Sylvia Dee, Rice University, Department of Earth, Environmental, and Planetary Sciences, Houston, TX, United States, Kim Cobb, Georgia Institute of Technology Main Campus, Department of Earth and Atmospheric Sciences, Atlanta, GA, United States, Julien Emile-Geay, Univ. of Southern California, Department of Earth Sciences, Los Angeles, CA, United States, Nathan John Steiger, University of Washington, Seattle, WA, United States, Toby Ault, Cornell University, Department of Earth and Atmospheric Science, Ithaca, NY, United States, Feng Zhu, University of Southern California, Department of Earth Sciences, Los Angeles, CA, United States, R. Lawrence Edwards, Nanjing Normal University, Dept. of Geography, Nanjing, China, Hai Cheng, University of Minnesota, Department of Earth Sciences, Minneapolis, MN, United States and Christopher D Charles, Scripps Institution of Oceanography, La Jolla, CA, United States
Recorded Presentation
Abstract:
The El Niño–Southern Oscillation (ENSO) shapes global climate patterns yet its sensitivity to external climate forcing remains uncertain. Modeling studies suggest that ENSO is sensitive to sulfate aerosol forcing associated with explosive volcanism but observational support for this effect remains ambiguous given the rarity of large volcanic eruptions and the short instrumental record. Here, we use sea surface temperature (SST) reconstructions derived from two data products to gauge ENSO’s response to large volcanic eruptions of the last millennium: (1) absolutely dated fossil corals from the central tropical Pacific, and (2) recently published paleoclimate data assimilation (DA) reconstructions. In the Palmyra coral data, superposed epoch analysis reveals a weak tendency for an El Niño–like response in the year after an eruption, but this response is not statistically significant, nor does it appear after the outsized 1257 Samalas eruption. In the DA reconstructions, the response is more nuanced, but provides limited evidence for an El Niño–like response of the tropical Pacific in the year following sufficiently large tropical volcanic eruptions. However, inconsistencies in both the spatial patterns and magnitudes between climate models and the DA reconstruction results indicate that current models may not adequately represent the regional tropical response of ENSO to volcanic forcing. Additionally, the Palmyra record represents the longest, best replicated, highest-resolution, and most proximal record to the center of ENSO variability currently available, while DA inherently incorporates model biases in the assimilation prior. Taken together, our results suggest that those models showing a strong ENSO response to volcanic forcing may overestimate the size of the forced response relative to natural ENSO variability.

This work highlights a role for high-resolution paleoclimate reconstructions and model simulations of LM volcanism in the assessment of potential geoengineering schemes designed to offset greenhouse warming in coming decades. Our work suggests that continued efforts toward data-model comparisons of the effects of volcanic eruptions on regional climate over the LM are critical to a robust assessment of the climatic effects of sulfate aerosol–induced geoengineering scenarios.

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