In previous regional nuclear war simulations, roughly 100 nuclear explosions with 15-KT (kilotons) TNT yields were estimated to ignite 1,300 square kilometers of urban and other developed land area.66 Toon et al., 2006, note 2.
View all notes
The resulting oxidation of carbonaceous materials (e.g., soils, biomass, fossil fuels, asphalt, plastics) was estimated to disperse >5 million metric tons (5 Tg C) of black carbon smoke particles into the stratosphere.77 Black carbon is the radiation-absorbing components of soot, which are elemental carbon and some condensed organics; V. Ramanathan and G. Carmichael, “Global and Regional Climate Changes due to Black Carbon,” Nature Geoscience 1, no. 4 (2008), 221–27.
View all notes
Most previous nuclear explosions have not produced significant black carbon emissions because they occurred in the U.S. Southwest desert, on small tropical islands, at high altitudes, or underground.88 K. Schaul, “Eight Countries. 2,056 Nuclear Tests. 71 Years—Mapped,” The Washington Post, 9 September 2016; SIPRI Yearbook 2014: Armaments, Disarmament, and International Security (Oxford, UK: Oxford University Press, 2014), 350.
View all notes

As a consequence of 5 Tg of black carbon being lofted into the stratosphere, solar radiation on land, atmospheric surface temperature, and rainfall would decrease globally and would likely result in a dramatic decrease in global agricultural production. Agricultural growing seasons could be reduced by 10 to 40 days per year for at least 5 years; global temperatures could be below normal for as long as 25 years; and immediate short-term temperatures could be colder than have occurred in the last 1,000 years.99 Toon et al., note 2.
View all notes
Precipitation could decrease by as much as 20% to 80% in the Asian monsoon region.1010 Black carbon emissions from fossil fuel and biomass burning have already been shown to decrease regional tropical rainfall from 1950 to 2002; Ramanathan and Carmichael, note 7.
View all notes
Large reductions in rainfall would occur in South America and southern Africa, and the American Southwest and Western Australia could be 20% to 60% drier. Climatic changes due to nuclear explosions on developed land could essentially produce a global “nuclear drought,” and the resulting famines could kill up to a billion people from starvation, which would probably most affect those communities that are already in food-insecure environments in the developing world, particularly in Sub-Saharan Africa, South Asia, and the Middle East.1111 Robock and Toon, note 2; J. D. Sachs, The Age of Sustainable Development (New York, NY: Columbia University Press, 2015).
View all notes
Significant changes in precipitation would probably also increase conflict in developing regions, although global temperature reductions may reduce social violence in the United States and other developed countries.12