Driscoll describes the inability of CMIP5 models to reproduce low latitude volcanic changes to the northern hemisphere polar vortex, and the resulting impact on the North Atlantic Oscillation. Link here (abstract below).
http://www.agu.org/pubs/crossref/pip/2012JD017607.shtml The described systematic model weakness has two notable consequences for potential inadvertent warming from low latitude SRM projects. Firstly, the NAO affects wind clearance of ice from the Arctic. A large number of papers on role of wind clearance of arctic sea ice are here: http://www.jamstec.go.jp/res/ress/masayo.ogi/ A time series graph of the NAO is available here http://www.cpc.ncep.noaa.gov/data/teledoc/nao_ts.shtml Secondly, observations show regional warming over northern Asia following tropical volcanic eruptions, which models cannot reproduce. This regional warming may affect spring snow cover, albedo, and permafrost melting (and consequential methane release). See link to Schaeffer paper showing projected permafrost carbon loss in a non-geoengineered future climate. onlinelibrary.wiley.com/doi/10.1111/j.1600-0889.2011.00527.x/abstract I understand that high latitude volcanos don't cause the NAO effect, which suggested that SRM at low latitudes may be ill advised. High latitude geoengineering is also suggested by MacCracken etc al 2012 http://www.earth-syst-dynam-discuss.net/3/715/2012/esdd-3-715-2012.html I'd value discussion of the above, as it's a surprising and potentially problematic result for proposed low latitude geoengineering schemes. A Coupled Model Intercomparison Project 5 (CMIP5) simulations of climate following volcanic eruptions 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 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. -- You received this message because you are subscribed to the Google Groups "geoengineering" group. To post to this group, send email to geoengineering@googlegroups.com. To unsubscribe from this group, send email to geoengineering+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/geoengineering?hl=en.
