Stratospheric aerosol, volcanic eruptions and climate

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Stratospheric aerosol has a significant--and occasionally drastic--impact on Earth's climate. Sitting roughly 15-30 km above the Earth's surface, stratospheric aerosol consists of tiny liquid and solid particles, which scatter and absorb radiation as it passes through the atmosphere. Sudden increases in the amount of stratospheric aerosol--for example due to the injection of sulfur to the stratosphere by large volcanic eruptions--lead to decreases in the intensity of solar radiation reaching the surface and global cooling. In fact, in the pre-industrial era, stratospheric aerosol perturbations produced by large volcanic eruptions were the most important cause of year-to-year global climate variability. Accurate reconstructions of the history of stratospheric aerosol are therefore essential to interpret records of past climate variability and test climate models, which underpin estimates of climate sensitivity and future climate change. My research program aims to advance understanding of stratospheric aerosol and its impacts on Earth's climate. The research program will improve understanding of processes that control the lifecycle of stratospheric aerosol. It will also produce new, improved reconstructions of stratospheric aerosol radiative forcing, building upon new fundamental understanding of the links between the atmosphere and the physical and radiative properties of aerosols. Finally, the research program will improve understanding of the role of stratospheric aerosol in past climate variations, and its potential impacts on future climate. These research objectives will be realized through the development and use of numerical models of aerosols, the atmosphere and climate ranging from simple idealized models to comprehensive coupled models. Model development will be guided by available aerosol observations, including retrievals from satellite- and ground-based instruments, as well as proxy records from polar ice cores and tree rings. The project will have a broad scientific impact, with findings relevant to fundamental understanding of atmospheric and aerosol processes and the causes of past climate variability, with implications for climate prediction and climate change policy. Results from the project will be relevant to a number of ongoing international activities, and to future Assessment Reports from the Intergovernmental Panel on Climate Change. The project will support advancement of Canadian climate modeling capabilities, contributing to the testing and development of modeling tools used in Canada to predict future climate and the effects of severe aerosol events including wildfires and volcanic eruptions.