The latest New Scientist (http://www.newscientist.com/) carries an article about injecting SO2 into the stratosphere. Observations of giant volcano eruptions have shown that this could reduce world temperature by 1 or 2 degrees for a year or two.
This was “seriously” proposed in USA a dozen years ago as the cheapest solution to the global warming problem. Groups which have been denying that there is a problem are now supporting this idea. Now the Russians are planning a large-scale test. New Scientist sadly predicts that it will happen.
Many countries are capable of doing it, and also large companies. There is no international agreement or law that prohibits it. Of course this treatment must then be repeated regularly, until a better solution is found.
I remember, in my school days, it was found that fish and other animals were dying in Scandinavia, because of SO2 being produced by British power stations. The rain was too acid. Since then, SO2 emissions have been greatly reduced. Stratospheric SO2 will come down into the oceans, and add to the acidification due to CO2.
cw