Uncertainties in recent volcanic aerosol optical depths and implications for global climate change

Abstract:

Volcanic eruptions exert a cooling effect on global climate, making the understanding of recent volcanoes of particular interest in light of the decrease in the rate of global warming since about 2000. Here we use lidar and balloon-borne observations to provide evidence that total radiative forcing resulting from recent eruptions is underestimated even when currently available satellite estimates are taken into account, owing to significant amounts of volcanic aerosol between the tropopause and 15 km at mid to high latitudes. We also demonstrate the ability of the AERONET sun-photometer network to detect stratospheric AOD (SAOD) volcanic enhancements and account for the full stratospheric perturbation above the tropopause that tracks other methods of observation at multiple latitudes. Using the AERONET data, we develop an uncertainty range for post-2000 SAOD and, using a simple climate model, determine the global volcanic aerosol forcing and related cooling since 2000. We find that recent volcanic events are very likely to have caused significantly more post-2000 cooling than implied by available satellite databases that cover stratospheric aerosols only above 15 km.