 Counterintuitively , the atmospheric temperature dropped to normal levels much more quickly at the larger impact sites than at the smaller sites : at the larger impact sites , temperatures were elevated over a region 15 @,@ 000 to 20 @,@ 000 km ( 9 @,@ 300 to 12 @,@ 400 mi ) wide , but dropped back to normal levels within a week of the impact . At smaller sites , temperatures 10 K higher than the surroundings persisted for almost two weeks . Global stratospheric temperatures rose immediately after the impacts , then fell to below pre @-@ impact temperatures 2 – 3 weeks afterwards , before rising slowly to normal temperatures . 
