Sea Ice Response to Volcanic Eruptions in Model Large Ensembles

Abstract:

Large volcanic eruptions have a substantial short-term impact on climate due to the injection of sulfate aerosols into the stratosphere. These aerosols cool the troposphere and warm the lower stratosphere over their lifetime. The spatial distribution of the aerosols and their associated climate impacts depend strongly on the location of the eruption, due to the transport of aerosols in the stratosphere by the Brewer-Dobson circulation. A further consideration is how shortwave radiative feedbacks depend on the time of year of the short-term volcanic aerosol forcing. Previous work had shown an asymmetric high latitude response to volcanoes in single models. However, multiple model large ensembles are needed to determine whether the asymmetry is model-dependent or a feature of the local response of the climate system.

In this work we make use of the large collection of model large ensembles of fully-coupled historical simulations from both CMIP5- and CMIP6-generation models to investigate the impact of historical volcanic eruptions on polar regions. We analyze the response to the Agung, El Chichon and Pinatubo eruptions, which have volcanic aerosol distributions that are Southern Hemisphere focused, Northern Hemisphere focused, and approximately symmetric, respectively. We find that, for the eruptions confined to one hemisphere, the sea ice expands most in that (same) hemisphere. However, the expansion is greater in the Arctic than in the Antarctic for the Pinatubo eruption. There is a delay of approximately one-year between the eruption and the peak sea ice response, allowing for volcanic aerosols to reach the pole and the cumulative decrease in absorbed shortwave radiation by the sea ice. In the Arctic, the response peaks in September, while the timing of the peak response in the Antarctic is inconsistent among models. Antarctic sea ice expands more and the Southern Ocean cools more in models of the CMIP5 generation than the CMIP6 generation. We draw two major conclusions from our results. First, the interannual predictability of Arctic sea ice may increase following large volcanic eruptions from which the aerosols propagate into the Northern Hemisphere. Second, the weak response of Antarctic sea ice in CMIP6 models is an inherent feature of the high-latitude Southern Ocean in models under both volcanic and CO2 forcing.