In a paper appearing in Nature Geoscience, Kate Ricke, a climate physicist at Carnegie Mellon University in Pittsburgh, Pennsylvania, and her team show, by modelling, that solar-radiation management could not only reduce rainfall in the long term, but its effects will also vary across regions. Some places will be over-cooled by atmospheric changes, which are too minor to be effective for their neighbours.
The gases under consideration are sulphur compounds that would produce sulphate aerosols in the upper atmosphere. Geoengineering advocates have suggested injecting large quantities of these materials into the stratosphere, either by shooting them up in artillery shells or releasing them from high-flying aeroplanes. Once there, they would disperse into a thin, bright haze that would reflect enough sunlight back into space to partially or completely offset global warming.
"It changes the distribution of energy in the troposphere so that it becomes more convectively stable," Nature quoted Ricke, as saying. Consequently, precipitation decreases.
Regional effects are also important. For example, Ricke said, her research demonstrates that levels of sulphate that kept China closest to its baseline climate were so high that they made India cold and wet.
Those that were best for India raised the mercury levels in China. However, both countries fared better either way than under a no-geoengineering policy, she said.
The researchers also found that all of these effects get worse with time.
Ricke said: "The compensation is imperfect. The longer you do it, the more imperfect it becomes."
This type of geoengineering is at best a temporary fix - something people working in the field had always known because it does nothing to prevent the accumulation of CO2 and the resulting acidification of the oceans.
"But it might be even more temporary than people had expected," Rickie said.
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