Impact of global warming on the rise of volcanic plumes and implications for future volcanic aerosol forcing

Abstract

Abstract Volcanic eruptions have a significant impact on climate when they inject sulfur gases into the stratosphere. The dynamics of eruption plumes is also affected by climate itself, as atmospheric stratification impacts plumes' height. We use an integral plume model to assess changes in volcanic plume maximum rise heights as a consequence of global warming, with atmospheric conditions from an ensemble of global climate models, using three representative concentration pathways (RCP) scenarios. Predicted changes in atmospheric temperature profiles decrease the heights of tropospheric and lowermost stratospheric volcanic plumes and increase the tropopause height, for the RCP4.5 and RCP8.5 scenarios in the coming three centuries. Consequently, the critical mass eruption rate required to cross the tropopause increases by up to a factor of 3 for tropical regions and up to 2 for high‐latitude regions. A number of recent lower stratospheric plumes, mostly in the tropics (e.g., Merapi, 2010), would be expected to not cross the tropopause starting from the late 21st century, under RCP4.5 and RCP8.5 scenarios. This effect could result in a ≃5–25% decrease in the average SO 2 flux into the stratosphere carried by small plumes, the frequency of which is larger than the rate of decay of volcanic stratospheric aerosol, and a ≃2–12% decrease of the total flux. Our results suggest the existence of a positive feedback between climate and volcanic aerosol forcing. Such feedback may have minor implications for global warming rate but can prove to be important to understand the long‐term evolution of volcanic atmospheric inputs. Plain Language Summary Volcanic eruptions cool climate when they inject sulfur gases above the tropopause, which is the separation between the troposphere and the stratosphere where air ceases to cool with height. However, climate can also impact volcanic eruptions as atmospheric conditions govern the rise of volcanic plumes. Here we use a volcanic plume model and climate models projections to investigate whether ongoing global warming could impact the height of volcanic plumes, and in turn the delivery of sulfur gases to the stratosphere.We show that projected climate change is expected to result into smaller volcanic plume height and a higher tropopause height. As a consequence, only more powerful eruptions, which are less frequent, would be able to inject sulfur gases above the tropopause and to cool climate. This effect could result in a 5‐25% decrease of the flux of volcanic sulfur gases into the stratosphere carried by small eruptions and a 2‐12% decrease of the total flux. Our results thus suggest that global warming will cause less volcanic cooling. Consequences for future rate of global warming may be minor, but the proposed mechanism may prove to be important to understand the long‐term evolution of volcanic atmospheric inputs. Key Points Projections of three GCMs imply that the maximum rise height of lowermost stratospheric volcanic plumes will decrease with global warming Decrease in plume height and increase in tropopause height will result in fewer stratopheric injections from volcanic eruptions Radiative forcing related to volcanic aerosol‐radiation interactions is predicted to decline, in turn