Evaluating the relationship between the temperature response to volcanic aerosols and climate sensitivity

Abstract

Climate sensitivity is an important concept in climate science, but its estimated value has considerable uncertainty. Some previous studies have argued for a link between the temperature response to volcanic radiative forcing and climate sensitivity. Bender et al. (2010) showed that equilibrium climate sensitivity is correlated across Coupled Model Intercomparison Project Phase 3 (CMIP3) models to the ratio of surface temperature response to top-of-atmosphere shortwave radiation response following Pinatubo, when excluding one anomalous model. In this thesis, Bender et al.'s calculation for CMIP3 models was repeated and was found to give a correlation coefficient of -0.44 (p = 0.23), which is lower than what Bender et al. found. Extension to Coupled Model Intercomparison Project Phase 5 (CMIP5) models also shows a lower correlation coefficient. Using transient climate response instead of equilibrium climate sensitivity or lower-troposphere temperature instead of surface air temperature in Bender et al.'s approach increased the correlation coefficient. Alternatively, regression of the temperature response on the shortwave radiative response and an ENSO index gave the highest correlation with climate sensitivity for a 7-year running mean surface temperature series (r = -0.65, p = 0.04) and a 7-year running mean lower-troposphere temperature series (r = -0.68, p = 0.03) based on CMIP5 models. Future work could explore the use of a transient climate response calculated from lower-troposphere temperature or a transient climate response of even shorter time-scale as alternative measures of climate sensitivity.