A nuclear war using only a small fraction of current global arsenals would quickly cause prolonged and catastrophic stratospheric ozone depletion. The impact on human and animal health and on fundamental ecosystems would be disastrous.
Scientists have known for more than two decades that a global nuclear war—an event that came perilously close during the Cold War between the US and the former Soviet Union, and which cannot be ruled out as long as those massive arsenals exist—would severely damage the Earth’s protective ozone layer. Studies in the 1980s by the US National Research Council and others showed that solar heating of the smoke produced by massive fires would displace and destroy significant amounts of stratospheric ozone.
Early in 2008, physicists and atmospheric scientists from the University of Colorado, UCLA, and the National Center for Atmospheric Research published important new findings that a regional nuclear war involving 100 Hiroshima-sized bombs would result in severe losses in stratospheric ozone.
The scientists concluded that a regional nuclear conflict between India and Pakistan in which each used 50 Hiroshima-sized weapons (~15 kt) would produce an estimated 6.6 teragrams (Tg) of black carbon.  In addition to the global surface cooling described above, large losses in stratospheric ozone would persist for years. The global mean ozone column would be depleted by as much as 25% for five years after the nuclear exchange. At mid-latitudes (25-45%) and at northern high latitudes (50-70%), ozone depletion would be even more severe and would last just as long.
Substantial increases in ultraviolet radiation would have serious consequences for human health. Those consequences, as we know from earlier studies of stratospheric ozone loss—the “ozone hole” that prompted the Montreal Protocol and the phasing out of ozone-depleting chlorofluorocarbons (CFCs)—include steep increases in skin cancer, crop damage, and destruction of marine phytoplankton.
Increased UV radiation is largely detrimental, damaging terrestrial and oceanic plants and producing skin cancer, ocular damage, and other health effects in humans and animals. Conclusive evidence shows that increased UV-B radiation damages aquatic ecosystems, including amphibians, shrimp, fish, and phytoplankton. …An analysis of biological sensitivity to UV spectral changes concluded that a 40% ozone column depletion at 45°N – as computed here – would increase DNA damage (believed related to carcinogenesis) by 213%, and plant damage (e.g., photoinhibition) by 132% relative to normal conditions. …Ozone losses at midlatitudes point to DNA effects in the range of 150% for five years or more.
— Michael J. Mills, Owen B. Toon, Richard P. Turco, Douglas E. Kinnison, Rolando R. Garcia. Massive global ozone loss predicted following regional nuclear conflict. Proceedings of the National Academy of Sciences. April 8, 2008
A 1-Tg infusion of soot would also dangerously deplete stratospheric ozone, although the effects would be smaller and shorter-lived than in the 5-Tg case. The study concluded that global mean ozone column losses would peak at 8% and that the perturbation would last up to four years. One of the most surprising findings is that the magnitude and duration of the predicted ozone reductions from the regional nuclear war considered by the scientists are greater than those calculated in the 1980s for global thermonuclear war with yields a thousand times greater.
 One teragram is a unit of mass equal to 1,000,000,000,000 (one trillion) grams.
Massive global ozone loss predicted following regional nuclear conflict. Michael J. Mills, Owen B. Toon, Richard P. Turco, Douglas E. Kinnison, and Rolando R. Garcia. PNAS April 8, 2008 vol. 105 no. 14 5307-5312.