We use 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 find 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> even after three years, constituting an extratropical "ozone hole." The resulting increases in UV radiation could impact the biota significantly, including serious consequences for human health.What's the catch? The authors are using the flawed 2007 Toon et al. study as the source of their figure for soot injection into the upper atmosphere. The authors assume that ALL targeted cities will produce mass fires with efficient pyroconvective pumping, that these fires will consume basically all available flammable material in the target cities, and that rainout will only remove 20% of the soot before it reaches the upper atmosphere. These are not valid assumptions, and real-world experience with atmospheric nuclear weapons detonations does not bear them out.
There is a fairly well-developed literature on fire effects from nuclear explosions- in particular, the work of Harold S. Brode, but also the work of civil defense researchers in both the United States and Soviet Union- that the authors of this study chose to conveniently ignore. There was actually considerable controversy regarding the extent of fire effects decades ago, which is described in a 2006 book by Lynn Eden, Whole World on Fire. Brode took the pessimistic view, arguing that mass fires would occur in most circumstances following nuclear explosions of yields in excess of a few hundred kilotons. Because modern strategic nuclear warheads all exceed this threshold, he postulated that fire effects would be far greater than had been predicted earlier. The civil defense researchers, meanwhile, used real-world experience to attempt to create a set of heuristics for understanding fire effects. They studied WWII bombing experience and were able to test real buildings in atmospheric nuclear tests. This memorable 1954 film is an example of their hands-on techniques:
The civil defense researchers concluded that firestorms were an unpredictable effect, responding strongly to the contingencies of weather, topography, fuel loading, and other factors. I'm personally a bit more sympathetic to their views than I am to Brode's, but Brode was no slouch- he is one of the foremost experts on nuclear weapons effects that the world has ever produced. But even Brode's relatively extreme views are incompatible with the bizarre assumptions made in the 2007 Toon et al. study, and consequently the many studies that now use its conclusions to model the effects of regional nuclear conflict. The extremely low 20% rainout value is particularly problematic- the authors have no real justification for it other than "because we used it in 1990, and it arguably happens this way in some forest fires." I have a hard time imagining that observers in the USSBS could possibly have missed noticing that the firestorms produced by Allied bombing had injected MOST OF THE MATERIAL IN THE TARGET CITIES into the upper atmosphere- which is the assumption that the study makes. (Examine section 6.1 to understand what I mean.) However, that doesn't keep them from telling reporters that their rainout value is one of their findings, rather than one of their assumptions:
"All the new models came up with the same results," Toon said, "and they gave us two surprises: One was the huge quantity of smoke that would be produced from even the limited nuclear war in our scenario, and the other was the conclusion that the smoke would remain dense above the stratosphere for as long as five years."Indeed, neither Hiroshima or Nagasaki appears to fit the assumptions made in the study- rainout at Hiroshima seems to have been pretty pronounced (the famous black rain), and Nagasaki failed to develop into a full-blown firestorm due to the local topography. In any case, rainout after a nuclear explosion is NOT the same as rainout resulting from a forest fire, as is attested by this 1988 study and this 1979 study of rainout following the atomic bombings in Japan. In short, Toon et al. really didn't do their research- at all.