In the event of a significant nuclear war, researchers (Paul Crutzen and John Birks initially) predicted that a barrier of smoke (from incinerated urban centres and forests) would fill tropospheric skies--and punch oxides of nitrogen and bomb debris into the stratosphere. Tropospheric smoke would---depending on the extent of the exchange---eventually surround the earth, reducing the tropospheric temperature and causing damage to ecosystems and atmospheric components such as stratospheric ozone. Others have calculated the size of nuclear explosions that are required to get bomb debris into the stratosphere: at mid to high latitudes where the tropopause is lower only 30 kiloton weapons are required; the U. S. atomic bombs used during the Second World War averaged less than 18 kilotons. At low latitudes, where the tropopause is highest, >1 megaton weapons are required to loft bomb debris into the stratosphere. ~Ambios, v11, pages 115-125, 1982. `