Climatic consequences of regional nuclear conflicts

Abstract

Abstract. We use a modern climate model and new estimates of smoke generated by fires in contemporary cities to calculate the response of the climate system to a regional nuclear war between emerging third world nuclear powers using 100 Hiroshima-size bombs (less than 0.03% of the explosive yield of the current global nuclear arsenal) on cities in the subtropics. We find significant cooling and reductions of precipitation lasting years, which would impact the global food supply. The climate changes are large and longlasting because the fuel loadings in modern cities are quite high and the subtropical solar insolation heats the resulting smoke cloud and lofts it into the high stratosphere, where removal mechanisms are slow. While the climate changes are less dramatic than found in previous "nuclear winter" simulations of a massive nuclear exchange between the superpowers, because less smoke is emitted, the changes are more long-lasting because the older models did not adequately represent the stratospheric plume rise.

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

“…Hence, if OC is co-emitted with BC particles, the aerosol particle scattering and absorption will be affected and consequently the self-lofting capacity of the fire plumes into the stratosphere and potentially the mesosphere. Therefore, it is important to investigate the impact of co-emissions of OC and BC on the fire plume height development and climate impacts that may differ from previous studies, which only BC emissions have been considered [e.g., Robock et al, 2007;Stenke et al, 2013;Mills et al, 2014].…”

“…In our experiments, we used the default values of optical properties for BC and POM in NorESM1-M, and we assume an initial effective radius of about 0.1 μm for BC and 0.4 μm for POM [see Table 1 in Kirkevåg et al, 2013]. Previous studies have used an effective radius for BC ranging between 0.05 and 0.1 μm [Robock et al, 2007;Mills et al, 2014]. We inject POM to account for the OC emissions that will occur during the fires.…”

“…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. All changes have devastating impacts on the agriculture productivity in regions far from the conflict [Toon et al, 2007b;Özdogan et al, 2013;Xia and Robock, 2013;Mills et al, 2014;Xia et al, 2015].…”

“…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.…”

“…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].…”