Effects of Nuclear War on Ozone Depletion

A limited nuclear war between India and Pakistan could produce catastrophic loss of stratospheric ozone globally, lasting a decade, as we have reported in Mills et al. (PNAS, 2008).  In that study, we used a chemistry-climate model and new estimates of smoke produced by fires in contemporary cities to calculate the impact on stratospheric ozone of a regional nuclear war between developing nuclear states involving 100 Hiroshima-size bombs exploded in cities in the northern subtropics. We found column ozone losses in excess of 20% globally, 25–45% at midlatitudes, and 50–70% at northern high latitudes persisting for 5 years, with substantial losses continuing for 5 additional years. Column ozone amounts remain near or <220 Dobson units at all latitudes even after three years, constituting a near-global “ozone hole.” The resulting increases in UV radiation could impact the biota significantly, including serious consequences for ecosystem services and human health.  We have recently calculated UV indices associated with such ozone depletions. We find that UVIs more than double the conventional maximum of 11 for that scale are prevalent in summer across all major continental landmasses.

The primary cause for the dramatic and persistent ozone depletion is heating of the stratosphere by smoke, which strongly absorbs solar radiation. The smoke-laden air rises to the upper stratosphere, where removal mechanisms are slow, so that much of the stratosphere is ultimately heated by the localized smoke injections. Higher stratospheric temperatures accelerate catalytic reaction cycles, particularly those of odd-nitrogen, which destroy ozone. In addition, the strong convection created by rising smoke plumes alters the stratospheric circulation, redistributing ozone and the sources of ozone-depleting gases, including N₂O and chlorofluorocarbons. The ozone losses predicted are significantly greater than previous “nuclear winter/UV spring” calculations, which did not adequately represent stratospheric plume rise. Our results point to previously unrecognized mechanisms for stratospheric ozone depletion. A nuclear war between the United States and Russia could produce even deeper and more widespread ozone depletion.