In a series of field measurements of ice crystals combined with cloud chamber experiments, Cziczo and colleagues found that lead makes a great ice condenser in stratospheric aerosols, a first report of this effect.
"Most of the lead in the atmosphere is not natural," Cziczo notes, but was spewed out in leaded gasoline in previous decades and is still used in light aircraft engines. Lead is one of the worst pollutants of the industrial age, linked to lowered intelligence scores, nerve damage and high blood pressure, among many other ills.
But plugging lead into a series of climate models, the Nature Geoscience study shows that high stratospheric lead levels would lead to ice clouds whose sunlight reflection would cut current global warming in half. "These are the kinds of emissions we might have seen in the late 1970's," Cziczo says. In past decades, lead pollution may have helped keep global warming at bay.
"The study helps to highlight why talk of geoengineering is something we shouldn't pursue now," he adds. "It's a bit arrogant to presume we understand aerosols so well we could not expect unintended consequences."