Hugh Pickens writes "Scientists estimate that the US Clean Air Act has cut a major air pollutant, sulfate aerosols, by 30% to 50% since the 1980s, helping greatly reduce cases of asthma and other respiratory problems. But NPR reports that this good news may have a surprising downside: cleaner air might actually intensify global warming. One benefit of sulfates is that they've been helpfully blocking sunlight from striking the Earth for many decades, by brightening clouds and expanding their coverage. Researchers believe greenhouse gases such as CO2 have committed the Earth to an eventual warming of roughly 4 degrees Fahrenheit, a quarter of which the planet has already experienced. But thanks to cooling by aerosols starting in the 1940s, the planet has felt only a portion of that warming. And unlike CO2, which persists in the atmosphere for centuries, aerosols last in the air for a week at most, so cutting them would probably rapidly accelerate global warming. The author of 'Hack the Planet' says: 'As we take away that unexpectedly helpful cooling mask, we're going to be facing more global warming than we expected.'"