Spraying sulfate particles, the method most likely to be implemented, is classified as a form of “solar radiation management,” an Orwellian term that some of its advocates have sought to reframe as “climate remediation.”

Yet if the “remedy” were fully deployed to reduce the earth’s temperature, then at least 10 years of global climate observations would be needed to separate out the effects of the solar filter from other causes of climatic variability, according to some scientists.

If after five years of filtered sunlight a disaster occurred — a drought in India and Pakistan, for example, a possible effect in one of the modeling studies — we would not know whether it was caused by global warming, the solar filter or natural variability. And if India suffered from the effects of global dimming while the United States enjoyed more clement weather, it would matter a great deal which country had its hand on the global thermostat.

So who would be turning the dial on the earth’s climate? Research is concentrated in the United States, Britain and Germany, though China recently added geoengineering to its research priorities.