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Model Simulations of Climatic Effects of Volcanic Eruptions
Reference
Driscoll, S., Bozzo, A., Gray, L.J., Robock, A. and Stenchikov, G. 2012. Coupled Model Intercomparison Project 5 (CMIP5) simulations of climate following volcanic eruptions. Journal of Geophysical Research 117: 10.1029/JD017607.

Background
The authors report that Stenchikov et al. (2006) analyzed seven models used in the Fourth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC, 2007) that "included all the models that specifically represented volcanic eruptions," finding that the strength and spatial pattern of the surface temperature anomalies predicted by them were not "well reproduced."

What was done
Hoping to find some improvement in more recent versions of the models, Driscoll et al. repeated the analysis of Stenchikov et al. (2006), using 13 model simulations from the Coupled Model Intercomparison Project phase 5 (CMIP5) - an overview of which is given by Taylor et al. (2011) - while focusing their analysis on the regional impacts of the largest volcanic eruptions on the Northern Hemisphere (NH) large-scale circulation during the winter season.

What was learned
In the words of the five researchers, "the models generally fail to capture the NH dynamical response following eruptions." More specifically, they say the models "do not sufficiently simulate the observed post-volcanic strengthened NH polar vortex, positive North Atlantic Oscillation, or NH Eurasian warming pattern, and they tend to overestimate the cooling in the tropical troposphere." They also state that "none of the models simulate a sufficiently strong reduction in the geopotential height at high latitudes," and that, correspondingly, "the mean sea level pressure fields and temperature fields show major differences with respect to the observed anomalies." In addition, they note that "all models show considerably less variability in high-latitude stratospheric winds than observed," and they say that "none of the models tested have a Quasi-Biennial Oscillation in them."

What it means
"With substantially different dynamics between the models," Driscoll et al. say they had "hoped to find at least one model simulation that was dynamically consistent with observations, showing improvement since Stenchikov et al. (2006)." But "disappointingly," as they continue, they found that "despite relatively consistent post volcanic radiative changes, none of the models manage to simulate a sufficiently strong dynamical response." Thus, they state that their study "confirms previous similar evaluations and raises concern for the ability of current climate models to simulate the response of a major mode of global circulation variability to external forcings," indicating that "this is also of concern for the accuracy of geoengineering modeling studies that assess the atmospheric response to stratosphere-injected particles."

References
Stenchikov, G., Hamilton, K., Stouffer, R.J., Robock, A., Ramaswamy, V., Santer, B. and Graf, H.-F. 2006. Arctic Oscillation response to volcanic eruptions in the IPCC AR4 climate models. Journal of Geophysical Research 111: 10.1029/2005JD006286.

Taylor, K.E., Stouffer, R.J. and Meehl, G.A. 2011. An overview of CMIP5 and the experiment design. Bulletin of the American Meteorological Society 93: 485-498.

Reviewed 30 January 2013