Atmospheric effects and societal consequences of regional scale nuclear conflicts and acts of individual nuclear terrorism

Abstract

Abstract. We assess the potential damage and smoke production associated with the detonation of small nuclear weapons in modern megacities. While the number of nuclear warheads in the world has fallen by about a factor of three since its peak in 1986, the number of nuclear weapons states is increasing and the potential exists for numerous regional nuclear arms races. Eight countries are known to have nuclear weapons, 2 are constructing them, and an additional 32 nations already have the fissile material needed to build substantial arsenals of low-yield (Hiroshima-sized) explosives. Population and economic activity worldwide are congregated to an increasing extent in megacities, which might be targeted in a nuclear conflict. We find that low yield weapons, which new nuclear powers are likely to construct, can produce 100 times as many fatalities and 100 times as much smoke from fires per kt yield as previously estimated in analyses for full scale nuclear wars using high-yield weapons, if the small weapons are targeted at city centers. A single "small" nuclear detonation in an urban center could lead to more fatalities, in some cases by orders of magnitude, than have occurred in the major historical conflicts of many countries. We analyze the likely outcome of a regional nuclear exchange involving 100 15-kt explosions (less than 0.1% of the explosive yield of the current global nuclear arsenal). We find that such an exchange could produce direct fatalities comparable to all of those worldwide in World War II, or to those once estimated for a "counterforce" nuclear war between the superpowers. Megacities exposed to atmospheric fallout of long-lived radionuclides would likely be abandoned indefinitely, with severe national and international implications. Our analysis shows that smoke from urban firestorms in a regional war would rise into the upper troposphere due to pyro-convection. Robock et al. (2007) show that the smoke would subsequently rise deep into the Correspondence to: O. B. Toon (toon@lasp.colorado.edu) stratosphere due to atmospheric heating, and then might induce significant climatic anomalies on global scales. We also anticipate substantial perturbations of global ozone. While there are many uncertainties in the predictions we make here, the principal unknowns are the type and scale of conflict that might occur. The scope and severity of the hazards identified pose a significant threat to the global community. They deserve careful analysis by governments worldwide advised by a broad section of the world scientific community, as well as widespread public debate.

Climate effects of a hypothetical regional nuclear war: Sensitivity to emission duration and particle composition

“…The estimated BC emissions (5 Tg) already take into account the initial rain-out as "black-rain" as described in detail in Toon et al [2007a]. After the initial month, the distribution of the BC particles in the atmosphere is substantially affected by the different injection duration (Figure 1).…”

“…on an investigation of available combustible mass loadings in Indian and Pakistan cities that will produce the 6 Tg of BC (5 Tg after "black rain" removal) [Toon et al, 2007a], there is probably at least 1-2 Tg of POM.…”

“…The first studies using global climate models (GCMs) to examine the impact of the particles [e.g., Turco et al, 1983] showed catastrophic climatic consequences of a nuclear war between superpowers, with subfreezing land temperatures even during summer. More recent studies, using state-of-the-art GCMs, have assessed the damage that might result from a more restrictive use of nuclear weapons [Robock et al, 2007;Toon et al, 2007aToon et al, , 2007bMills et al, 2008;Stenke et al, 2013]. These studies assume that a regional conflict over India/Pakistan involving 50 Hiroshima-size bombs could generate up to 5 Tg of black carbon (BC) in the upper-troposphere/lower stratosphere after an initial 20% removal as "black rain" [Toon et al, 2007a].…”

“…More recent studies, using state-of-the-art GCMs, have assessed the damage that might result from a more restrictive use of nuclear weapons [Robock et al, 2007;Toon et al, 2007aToon et al, , 2007bMills et al, 2008;Stenke et al, 2013]. These studies assume that a regional conflict over India/Pakistan involving 50 Hiroshima-size bombs could generate up to 5 Tg of black carbon (BC) in the upper-troposphere/lower stratosphere after an initial 20% removal as "black rain" [Toon et al, 2007a]. Even for such a scenario, the effects of the particles on the solar radiation would lead to colder and drier conditions for years after the conflict [Robock et al, 2007;Toon et al, 2007a], together with enhanced ultraviolet radiation owing to massive ozone destruction [Mills et al, 2008].…”

“…These studies assume that a regional conflict over India/Pakistan involving 50 Hiroshima-size bombs could generate up to 5 Tg of black carbon (BC) in the upper-troposphere/lower stratosphere after an initial 20% removal as "black rain" [Toon et al, 2007a]. Even for such a scenario, the effects of the particles on the solar radiation would lead to colder and drier conditions for years after the conflict [Robock et al, 2007;Toon et al, 2007a], together with enhanced ultraviolet radiation owing to massive ozone destruction [Mills et al, 2008]. Using a GCM, Robock et al [2007] estimated that such a BC injection reduces the global-average surface short-wave radiation by a maximum of about 16 W m −2 (after about 5 months) and decreases the global mean surface temperature by 1.3 ∘ C. The BC injection also modifies the precipitation associated with the Asian summer monsoon.…”