 What share, generally speaking, of greenhouse emissions were attributable to the U.S. at the time relative to the rest of the world? At the time, the U.S. was far and away the largest emitter in the world, emitting more than half of all of carbon emissions and the largest historical emitter. So, you know, carbon does not care about what year it was emitted. Carbon's in the air and it takes a while to go away.