Interactions between climate and the rise of explosive volcanic plumes : a new feedback in the Earth system.

Volcanic plumes rising above the tropopause inject SO₂ directly into the stratosphere, where it forms sulfate aerosols that modulate Earth’s radiative balance. Stratospheric volcanic sulfate aerosol forcing reduces Earth’s surface temperature and is a predominant driver of climate variability. The processes that govern the volcanic injection of SO₂ into the stratosphere are controlled to a large extent by climate. Thus, climate changes may affect stratospheric volcanic SO₂ inputs, volcanic forcing and climate, in turn. The assessment of this potential feedback is hindered by difficulties in understanding and constraining observationally the key processes governing plume rise. To address this challenge, we compile a new exhaustive database of eruption source parameters, along with their uncertainties (Aubry et al., 2017b). We apply these data along with the results of laboratory experiments to compare the performances of our newly proposed and published scalings for predicting volcanic plume heights. We demonstrate that plume heights are captured better by scalings accounting for atmospheric conditions (Aubry et al., 2017b). Furthermore, we evaluate 1D models of volcanic plume using the experimental and natural eruption datasets. We show that these new datasets enable reliable constraints on processes critical to plume rise including the rate of entrainment of atmosphere as well as the role condensation of water vapor (Aubry et al. (2017a) and Chapter 4). Significant limitations in the compiled data remain and we identify future improvements required to improve plume models evaluation. Next, we explore the impacts of climate projections for ongoing global warming on the rise height of volcanic plumes and SO₂ injection into the stratosphere. Our results reveal a novel feedback where global warming will reduce stratospheric injections of SO₂ by explosive eruptions (Aubry et al., 2016). This would lead to reduced volcanic forcing and surface cooling, and enhance global warming, in turn. To test this feedback, we develop a new idealized model of volcanic aerosol forcing and show that the proposed feedback may have important implications if greenhouse gas concentrations continue to increase at currents rates (Chapter 6). An exciting future direction is to assess interactions among the proposed feedback with other published climate-volcano feedbacks.Science, Faculty ofEarth, Ocean and Atmospheric Sciences, Department ofGraduat