Abstract
AbstractThe relationship between volcanic stratospheric aerosol optical depth (SAOD) and volcanic radiative forcing is key for quantifying volcanic climate impacts. In their Fifth Assessment Report, the Intergovernmental Panel on Climate Change used one scaling factor between volcanic SAOD and volcanic forcing based on climate model simulations of the 1991 Mt. Pinatubo eruption, which may not be appropriate for all eruptions. Using a large ensemble of aerosol‐chemistry‐climate simulations of eruptions with different sulfur dioxide emissions, latitudes, emission altitudes, and seasons, we find that the effective radiative forcing (ERF) is on average 20% less than the instantaneous radiative forcing, predominantly due to a positive shortwave cloud adjustment. In our model, the volcanic SAOD‐ERF relationship is non‐unique and varies widely depending on time since an eruption, eruption latitude, and season due to differences in aerosol dispersion and incoming solar radiation. Our revised SAOD‐ERF relationships suggest that volcanic forcing has been previously overestimated.
Highlights
Volcanic sulfate aerosol, formed in the stratosphere following the release of sulfur dioxide (SO2) during explosive volcanic eruptions, scatters incoming shortwave radiation (ISW) and absorbs longwave (LW) radiation, which leads to surface cooling that has defined the natural variability of climate over the last millennium (Myhre et al, 2013; Schurer et al, 2013; Sigl et al, 2015).Stratospheric aerosol optical depth (SAOD), which is a measure of the opacity of the stratosphere, is a key property used to estimate the radiative forcing of an eruption
We find that the conversion between stratospheric aerosol optical depth (SAOD) and effective radiative forcing (ERF) depends on the time after an eruption, eruption latitude, and eruption season because of differences in the aerosol distribution and the magnitude of the incoming solar radiation that result in differences in the magnitude of the instantaneous radiative forcing (IRF)
We have shown that the SAOD to ERF relationship is non‐unique and varies widely depending on the aerosol distribution and incoming solar radiation and the time after an eruption, eruption season, and eruption latitude
Summary
Volcanic sulfate aerosol, formed in the stratosphere following the release of sulfur dioxide (SO2) during explosive volcanic eruptions, scatters incoming shortwave radiation (ISW) and absorbs longwave (LW) radiation, which leads to surface cooling that has defined the natural variability of climate over the last millennium (Myhre et al, 2013; Schurer et al, 2013; Sigl et al, 2015).Stratospheric aerosol optical depth (SAOD), which is a measure of the opacity of the stratosphere, is a key property used to estimate the radiative forcing of an eruption. A constant relationship between SAOD and volcanic forcing is assumed; in the Fifth Assessment Report from the Intergovernmental Panel on Climate Change (IPCC AR5, Myhre et al, 2013), a forcing scaling factor of −25 W m−2 per unit change of volcanic SAOD is used. This factor was based on simulations of the 1991 eruption of Mt. Pinatubo in the Goddard Institute for Space Studies (GISS) model E (Hansen et al, 2005).
Sign-in/Register to view highlights & summary 
Published Version (
Free)
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call