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Journal Article

Small global-mean cooling due to volcanic radiative forcing


Mauritsen,  T.
Climate Dynamics, The Atmosphere in the Earth System, MPI for Meteorology, Max Planck Society;

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Gregory, J., Andrews, T., Good, P., Mauritsen, T., & Forster, P. (2016). Small global-mean cooling due to volcanic radiative forcing. Climate Dynamics, 47, 3979-3991. doi:10.1007/s00382-016-3055-1.

Cite as: http://hdl.handle.net/11858/00-001M-0000-002A-1534-4
In both the observational record and atmosphere-ocean general circulation model (AOGCM) simulations of the last (Formula presented.)150 years, short-lived negative radiative forcing due to volcanic aerosol, following explosive eruptions, causes sudden global-mean cooling of up to (Formula presented.)0.3 K. This is about five times smaller than expected from the transient climate response parameter (TCRP, K of global-mean surface air temperature change per W m−2 of radiative forcing increase) evaluated under atmospheric CO2 concentration increasing at 1 % yr−1. Using the step model (Good et al. in Geophys Res Lett 38:L01703, 2011. doi:10.1029/2010GL045208), we confirm the previous finding (Held et al. in J Clim 23:2418–2427, 2010. doi:10.1175/2009JCLI3466.1) that the main reason for the discrepancy is the damping of the response to short-lived forcing by the thermal inertia of the upper ocean. Although the step model includes this effect, it still overestimates the volcanic cooling simulated by AOGCMs by about 60 %. We show that this remaining discrepancy can be explained by the magnitude of the volcanic forcing, which may be smaller in AOGCMs (by 30 % for the HadCM3 AOGCM) than in off-line calculations that do not account for rapid cloud adjustment, and the climate sensitivity parameter, which may be smaller than for increasing CO2 (40 % smaller than for 4 × CO2 in HadCM3). © 2016 The Author(s)