Title: Human-Induced Modifications of Stratospheric Aerosols: Unintentional Impacts, Uncertainties, and the Prospect of Intentional Climate Intervention.
Abstract: Stratospheric aerosols play an important role in influencing both climate and stratospheric ozone levels. The chemical identity of aerosol is important as heterogenous reactions on aerosol surfaces control activation of ozone destroying substances and the spectroscopic properties together with the size distribution determine the impact on climate. Traditionally, stratospheric aerosol has been assumed to consist of sulfuric acid. However, it has become clear that in the lower stratosphere, where most of the stratospheric aerosol mass resides, organic/biomass-burning aerosol with poorly constrained chemical and optical properties is abundant. This represents a significant uncertainty especially in a changing climate, with changing troposphere-stratosphere exchange and increasing wildfire frequency. In addition, to these unintentional modifications of stratospheric aerosol by human activities, potential intentional modification of radiative forcing via injection of stratospheric aerosol, often referred to as solar radiation management or climate intervention, will be discussed, in particular its risks and efficacy.
Bio: Born in Tübingen, Germany, Frank Keutsch received his Diplom in chemistry from the Technische Universität München, Germany, under the supervision of Vladimir E. Bondybey in 1997. He received his Ph.D. in physical chemistry from the University of California at Berkeley in 2001. His graduate research was conducted under the direction of Richard J. Saykally and focused on vibration−rotation−tunneling spectroscopy and hydrogen-bond-breaking dynamics in water clusters. After working on stratospheric chemistry in the Department of Chemistry and Chemical Biology at Harvard University under the direction of James G. Anderson, he started his independent academic career in 2005 at the University of Wisconsin-Madison. He then moved to his current position as Stonington Professor of Engineering and Atmospheric Science at Harvard University. His research combines laboratory and field experiments with instrument development to investigate fundamental mechanisms of anthropogenic influence on atmospheric composition within the context of impacts on climate, humans and the environment.
Key Words: Climate, Spectroscopic Properties, Heterogeneous Chemistry
Faculty Host: Tim Bertram