Thursday, September 6, 2012

New paper finds climate models are unable to simulate effects of large volcanic eruptions

A paper published today in the Journal of Geophysical Research finds that current climate models are unable to simulate the climate following large volcanic eruptions, a major cause of natural climate variability. According to the authors, the paper confirms others with the same findings and "raises concern for the ability of current climate models to simulate the response of a major mode of [climate change]." 

The paper adds to many others showing current climate models are unable to model climate change due to natural changes in solar activity, ozone, ocean oscillations, volcanic eruptions, and clouds.

Key Points
  • Large volcanic eruptions cause a major dynamical response in the atmosphere
  • CMIP5 models are assessed for their ability to simulate this response
  • No models in the CMIP5 database sufficiently represent this response
Simon Driscoll
Alessio Bozzo
Lesley J. Gray
Alan Robock
Georgiy Stenchikov
The ability of the climate models submitted to the Coupled Model Intercomparison Project 5 (CMIP5) database to simulate the Northern Hemisphere winter climate following a large tropical volcanic eruption is assessed. When sulfate aerosols are produced by volcanic injections into the tropical stratosphere and spread by the stratospheric circulation, it not only causes globally averaged tropospheric cooling but also a localized heating in the lower stratosphere, which can cause major dynamical feedbacks. Observations show a lower stratospheric and surface response during the following one or two Northern Hemisphere (NH) winters, that resembles the positive phase of the North Atlantic Oscillation (NAO). Simulations from 13 CMIP5 models that represent tropical eruptions in the 19th and 20th century are examined, focusing on the large-scale regional impacts associated with the large-scale circulation during the NH winter season. The models generally fail to capture the NH dynamical response following eruptions. They do not sufficiently simulate the observed post-volcanic strengthened NH polar vortex, positive NAO, or NH Eurasian warming pattern, and they tend to overestimate the cooling in the tropical troposphere. The findings are confirmed by a superposed epoch analysis of the NAO index for each model. The 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. This is also of concern for the accuracy of geoengineering modeling studies that assess the atmospheric response to stratosphere-injected particles.

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