For more than a century, the same industrial activity that warmed the planet also quietly cooled it, as sulphur pollution scattered sunlight back toward space like dust on a greenhouse window. Now, as clean-air policies remove that veil, scientists are confronting an uncomfortable possibility: the Earth's climate may be 25 percent more sensitive to greenhouse gases than our best models assumed, and the warming we have long anticipated may arrive harder and sooner than projected. The past three years of record heat, a tripling of Earth's energy imbalance, and the disappearance of reflective low