There is an interesting seminar scheduled for September 27 2011. The announcement is reproduced below. Alan Robock and I differ on a number of climate issues, but he and I seem to agree on the risks of geoengineering. Alan told me that his papers on geoengineering can be obtained from http://climate.envsci.rutgers.edu/robock/robock_geopapers.html
I have highlighted text in the announcement in which he and I agree. His concern on geoengineering, which involves deliberate alterations in regional climate forcings, in addition to any effect on the global average radiative forcing, should also make him a proponent of the important role of land use/land cover change (i.e. a regional climate forcing) as a first-order climate forcing.
Date: Mon, 19 Sep 2011 08:55:42 -0600
From: Baylor Fox-Kemper
…. Tuesday, September 27, 2011 – 3:30pm
…. Smoke and mirrors: Is geoengineering a solution to global warming? 
In response to the global warming problem, there has been a recent renewed interest in geoengineering solutions involving solar radiation management by injecting particles into the stratosphere, brightening clouds, or blocking sunlight with satellites between the Sun and Earth. While volcanic eruptions have been suggested as innocuous examples of stratospheric aerosols cooling the planet, the volcano analog actually argues against geoengineering because of ozone depletion and regional hydrologic responses.
In this talk, I describe different proposed geoengineering designs, and then show climate model calculations that evaluate both their efficacy and their possible adverse consequences. No such systems to conduct geoengineering now exist, but a comparison of different proposed stratospheric injection schemes, using airplanes, balloons, and artillery, shows that using airplanes to put sulfur gases into the stratosphere would not be expensive.
Nevertheless, it would be very difficult to create stratospheric sulfate particles with a desirable size distribution. We have just started a GeoMIP project to conduct standard stratospheric aerosol injection scenarios in the context of CMIP5, so as to examine the robustness of the few experiments conducted so far.
If there were a way to continuously inject SO2 into the lower stratosphere, it would produce global cooling, stopping melting of the ice caps, and increasing the uptake of CO2 by plants. But there are at least 25 reasons why geoengineering may be a bad idea.These include disruption of the Asian and African summer monsoons, reducing precipitation to the food supply for billions of people; ozone depletion; no more blue skies; reduction of solar power; and rapid global warming if it stops. Furthermore, the prospect of geoengineering working may reduce the current drive toward reducing greenhouse gas emissions, there are concerns about commercial or military control, and it may seriously degrade terrestrial astronomy and satellite remote sensing. Global efforts to reduce anthropogenic emissions and to adapt to climate change are a much better way to channel our resources to address anthropogenic global warming.
Building: Mesa Lab, Room/Location: ML-132
Presenter(s): Alan Robock