Research funded in part by CPO’s Climate Observations and Monitoring (COM) program examines the response of the El Niño-Southern Oscillation (ENSO) to volcanic forcing over the last millennium. In a recent paper published in Science, authors analyze new paleoclimate data in the form of coral samples from the Tropical Pacific. These include a consistent proxy record for variables such as sea surface temperature. Analysis shows that the response of ENSO to volcanic forcing is either absent or difficult to detect. There is an El-Nino-like warmer-temperature response following volcanic eruptions; however, the volcanic impact is small relative to natural variability. Authors suggest their findings are consistent with the claim that most, if not all, of the variability exhibited by ENSO over the preindustrial portion of the last millennium is linked to internal climate variability, rather than external forcing.
These paleoclimate proxy data provide an independent validation for model studies and highlight the discrepancy between data and climate models regarding the sensitivity of the tropical Pacific to external forcing, which is potentially due to a number of factors including structural uncertainties in modeled stratospheric aerosol physics.
Authors emphasize that studies such as this one also play an important modern-day role in the assessment of potential geoengineering schemes designed to offset greenhouse warming. Understanding how major climate modes, such as ENSO, respond to stratospheric aerosol loading (like during a volcanic eruption, or during a geoengineering experiment) is key to assessing regional climate impacts under solar radiation management scenarios.