Adverse Impacts of Geoengineering by Stratospheric Aerosol Injection Methods

D.Weisenstein (1), P. Heckendorn (2), J. Pierce (3), T. Peter (2), D. Keith (4)

(1) Atmospheric and Environmental Research, Inc., Lexington, MA, USA (2) Institute for Atmospheric and Climate Science, ETH Zurich, Zurich, Switzerland, (3) Department of Physics and Atmospheric Science, Dalhousie University, Halifax, NS, Canada, (4) Energy and Environmental Systems Group, University of Calgary, Calgary, AB, Canada

     Abstract Number: 287
     Last modified: May 4, 2010

Abstract
This talk will focus on unintended adverse consequences of geoengineering by stratospheric aerosol injection to the chemistry and dynamics of the stratosphere. Such consequences include changes in stratospheric transport, heating of the tropical tropopause due to IR absorption by sedimenting aerosols, increases in stratospheric water vapor and HO$_x due to tropopause heating, and ozone depletion due to a combination of heterogeneous chemistry, changes in HO$_x, and changes in temperature and transport. We consider three different geoengineering scenarios: injection of SO$_2 at the equator and 20 km, injection of SO$_2 over a broad tropical region from 30S-30N and 20-25 km, and injection of H$_2SO$_4 from aircraft over a broad tropical region. These scenarios differ in the size of aerosol particles generated, the lifetime of those particles, and the shortwave scattering efficiency of the particles. To achieve a -4 W/m$^2 shortwave forcing to counteract a doubling of CO$_2, 8-10 MT-S/yr are required by H$_2SO$_4 injection across the tropics, ~20 MT-S/yr by SO$_2 injection across the tropics, and ~75 MT-S/yr by SO$_2 injection at the equator and 20 km. When compared by equivalent shortwave forcing, the H$_2SO$_4 method is far superior to the SO$_2 injection method, though stratospheric impacts are still troubling.