Customize several Gulfstream business jets with military engines and with equipment to produce and disperse fine droplets of sulfuric acid. Fly the jets up around 20 kilometers—significantly higher than the cruising altitude for a commercial jetliner but still well within their range. The planes spray the sulfuric acid, carefully controlling the rate of its release. The sulfur combines with water vapor to form sulfate aerosols, fine particles less than 1 micrometer in diameter. These get swept upward by natural wind patterns and are dispersed over the globe, including the poles. Once spread across the stratosphere, the aerosols will reflect ~1% of the sunlight hitting Earth back into space. Increasing the planet’s albedo will partially offset the warming effects caused by rising levels of greenhouse gases.

If operations were begun in 2020, it would take 25k tons of sulfuric acid to cut global warming 50% after 1 year. Once underway, the injection of sulfuric acid would proceed continuously. By 2040, 11 jets delivering ~250k tons of it each year, at an annual cost of $700m, would be required to compensate for the increased warming caused by rising levels of CO2. By 2070, the program would need to be injecting a bit more than 1m tons per year using a fleet of 100 aircraft. One of the startling things about Keith’s proposal is just how little sulfur would be required. A few grams of it in the stratosphere will offset the warming caused by a ton of CO2

since these schemes are cheap enough and consensus unobtainable (who gets a say?) we’ll very likely see surprise unilateral action by rich individuals, companies or states once the situation gets dire enough.

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