10 March 2016

Volcanic Aerosols in Climate Models


Although explosive volcanic injections of sulfur into the stratosphere are an important aerosol source, estimates of the climate impact of such aerosols have heretofore been limited to scattering of solar radiation by the aerosols. The effects on clouds after the particles settle into the troposphere have been neglected. Recently a team from the National Center for Atmospheric Research, DOE’s Pacific Northwest National Laboratory, the University  of Leeds and the Massachusetts Institute of Technology replaced a specified representation of volcanic aerosols in a global climate model with a physically-based treatment that starts with stratospheric injections of sulfur dioxide gas into the stratosphere, oxidizes it to form sulfuric acid vapor which forms new particles and condenses on existing particles, which gradually settle out of the stratosphere and then are scavenged from the atmosphere by clouds. The team was able to show that the model simulates the surface area of the aerosol quite realistically, which means that it will simulate scattering of sunlight accurately. Moreover, for the first time, the effect of explosive volcanic sulfur injections on clouds can be simulated in a global climate model. The new representation enables estimates of volcanic aerosol effects on the radiative properties of clouds and hence climate.

Volcanic aerosols have been prescribed in all previous climate simulations. A new study simulates the evolution, transport and removal of sulfate aerosols formed after injection of sulfur dioxide into the stratosphere by explosive eruptions from volcanoes. Now, for the first time, such effects can be simulated, and enables estimates of volcanic aerosol effects on the radiative properties of clouds and hence climate.

Steven J. Ghan
National Center for Atmospheric Research (NCAR)
Mills, MJ, A Schmidt, R Easter, S Solomon, DE Kinnison, SJ Ghan, RR Neely III, DR Marsh, A Conley, CG Bardeen, and A Gettelman.  2016.  "Global Volcanic Aerosol Properties Derived from Emissions, 1900-2014, using CESM1(WACCM)."  Journal of Geophysical Research: Atmospheres early view, doi:10.1002/2015JD024290.

We thank David Ridley for providing lidar extinction measurements shown in Figure 5, and Nicolas Theys for providing SO2 flux data for the database. Mauna Loa lidar data was provided by NOAA ESRL Global Monitoring Division, Boulder, Colorado, USA (http://esrl.noaa.gov/gmd/). Ny-Ålesund lidar data was provided by Christoph Ritter. We thank Anne Smith, Jean-François Lamarque, and two anonymous reviewers for many helpful comments on this manuscript. The National Center for Atmospheric Research is sponsored by the National Science Foundation. Any opinions, findings and conclusions or recommendations expressed in the publication are those of the author(s) and do not necessarily reflect the views of the National Science Foundation. SS was supported by NSF atmospheric chemistry program grant 1539972. Our global volcanic aerosol reconstruction may be accessed via doi:10.5065/D6S180JM. Supporting data are included as four tables in .xlsx format files and one figure; any additional data, including the source code used for these simulations, may be obtained from MJM (email: mmills@ucar.edu).