Investigating Stratospheric Aerosols: Volcanic Eruptions and Climate Intervention

Abstract

This thesis explores stratospheric aerosols in the context of volcanic eruptions and climate intervention methods. Periodic explosive volcanic eruptions can inject sulfur dioxide into the stratosphere, forming reflective sulfate aerosols and resulting in a reduction of surface air temperatures. The rising global temperatures and resulting environmental impacts brought about by climate change have prompted research into methods of deliberate climate intervention that seek to reduce global warming. This thesis begins with an introduction to the climate system and stratospheric aerosols. Then the current state of the literature surrounding solar climate intervention methods and their impacts is presented. The ability of the UK Earth System Model to accurately represent the 2019 Raikoke volcanic eruption is evaluated using a variety of observations. It is found that a simple injection of sulfur dioxide is not sufficient to reproduce the aerosol lifetime and distribution in the stratosphere, however including volcanic ash improves the model significantly. Once the model has been evaluated, the impact of two stratospheric aerosol injection (SAI) strategies, a method of solar climate intervention, are compared. In agreement with other modelling studies, the location of injection is found to significantly change the climate response to SAI. When compared with the target scenario the multi-latitude strategy reduces changes to large-scale circulation and dynamics, reducing the impact on regional temperature and precipitation responses, relative to a quasi- equatorial injection. The impact on extreme climate events is further investigated using the multi-latitude strategy. Analysis suggests that SAI can reduce the risk of increasing temperature and precipitation extremes, although its effectiveness varies regionally. In some areas this SAI strategy was able to reduce extreme temperatures more than the mean, minimising risk to society and ecosystems. The risk of wildfires under SAI was also explored and found to be reduced when compared to a global warming scenario.