There’s a cheap, quick, dirty, and controversial way to combat global warming that isn’t on the agenda of the United Nations climate summit in Paris, which runs from Nov. 30 to Dec. 11. It involves replicating the planet-cooling effect of a volcanic eruption. When Mount Pinatubo in the Philippines blew in 1991, its emissions briefly reversed most of the global warming that had occurred since the start of the Industrial Revolution. The idea is to mimic Pinatubo by using a fleet of modified business jets to inject fine droplets of sulfuric acid into the stratosphere, where they would combine with water vapor to form fine sulfate particles that reflect sunlight away from the earth.
Scientists estimate that a few grams of sulfate would be enough to counteract the warming effect of a ton of carbon dioxide. The cost of this planetary protection? Perhaps 0.01 percent of the annual world gross domestic product. In other words, almost nothing. The cost of stopping the entire planet from warming would be not much more per decade than the $6 billion the Italian government is spending to protect one city, Venice, from rising sea levels. That’s the calculation of a leading figure in the debate over so-called geoengineering, David Keith, a professor of applied physics at Harvard and of public policy at Harvard’s Kennedy School of Government.