Geoengineering may reduce temperatures globally, but there will still be local losers and winners--places that experience too much or too little rainfall, places subject to sudden temperature extremes. And no matter how much sulfur dioxide humankind throws into the heavens, the carbon dioxide will remain; to counteract the ever-increasing total, more sulfur must be launched into the air every year. Indeed, stopping it suddenly would be disastrous; all the hidden-away warming would emerge in a few months.