David Keith, a researcher at Harvard University and a leading expert on the subject, has suggested that if this kind of geoengineering, called solar radiation management, or S.R.M., is ever undertaken, it should be done slowly and carefully, so it could be halted if damaging weather patterns or other problems arose. The goal should only be to slow the rate that the atmosphere is warming under climate change, he said, not to reverse it.....
Very little money is set aside worldwide for geoengineering research. But even the suggestion of conducting field experiments can cause an uproar.
"People like lines in the sand to be drawn, and there's a very obvious one which says, fine, if you want to do stuff on a desktop or a lab bench, that's O.K.," said Matthew Watson, a researcher at the University of Bristol in Britain. "But as soon as you start going out into the real world, then that's different."
Dr. Watson knows all about those lines in the sand: He led a geoengineering research project, financed by the British government, that included a relatively benign test of one proposed technology. In 2011, the researchers planned to tether a balloon about a half-mile in the sky and try to pump a small amount of plain water up to it through a hose.
The proposal prompted protests in Britain, was delayed for half a year and then canceled, although ostensibly for other reasons.
In the United States, Dr. Keith and his colleagues have proposed a balloon experiment that would test the effect of sulfate droplets on atmospheric ozone — a potential trouble spot for solar engineering. Dr. Keith receives some private money from Bill Gates, the founder of Microsoft, for his geoengineering research, but says that for this experiment, which could cost $10 million or more, most of the funds would have to come from the government, for reasons of accountability and transparency.
