Climate Impact of a Regional Nuclear Weapons Exchange: An Improved Assessment Based On Detailed Source Calculations

Abstract

We present a multiscale study examining the impact of a regional exchange of nuclear weapons on global climate. Our models investigate multiple phases of the effects of nuclear weapons usage, including growth and rise of the nuclear fireball, ignition and spread of the induced firestorm, and comprehensive Earth system modeling of the oceans, land, ice, and atmosphere. This study follows from the scenario originally envisioned by Robock, Oman, Stenchikov, et al. (2007, https://doi.org/10.5194/acp-7-2003-2007), based on the analysis of Toon et al. (2007, https://doi.org/10.5194/acp-7-1973-2007), which assumes a regional exchange between India and Pakistan of fifty 15 kt weapons detonated by each side. We expand this scenario by modeling the processes that lead to production of black carbon, in order to refine the black carbon forcing estimates of these previous studies. When the Earth system model is initiated with 5 × 109 kg of black carbon in the upper troposphere (approximately from 9 to 13 km), the impact on climate variables such as global temperature and precipitation in our simulations is similar to that predicted by previously published work. However, while our thorough simulations of the firestorm produce about 3.7 × 109 kg of black carbon, we find that the vast majority of the black carbon never reaches an altitude above weather systems (approximately 12 km). Therefore, our Earth system model simulations conducted with model‐informed atmospheric distributions of black carbon produce significantly lower global climatic impacts than assessed in prior studies, as the carbon at lower altitudes is more quickly removed from the atmosphere. In addition, our model ensembles indicate that statistically significant effects on global surface temperatures are limited to the first 5 years and are much smaller in magnitude than those shown in earlier works. None of the simulations produced a nuclear winter effect. We find that the effects on global surface temperatures are not uniform and are concentrated primarily around the highest arctic latitudes, dramatically reducing the global impact on human health and agriculture compared with that reported by earlier studies. Our analysis demonstrates that the probability of significant global cooling from a limited exchange scenario as envisioned in previous studies is highly unlikely, a conclusion supported by examination of natural analogs, such as large forest fires and volcanic eruptions.

Rapidly expanding nuclear arsenals in Pakistan and India portend regional and global catastrophe

“…Significantly, the adopted fuel loading in the affected area (1.07 g/cm 2 in the ignition zone) was about one order of magnitude smaller than that in the most sparsely populated urban area considered in the present study, i.e., the 100th city attacked in Pakistan (refer to table S3). Accordingly, the preliminary findings in ( 38 ) are not representative of the fires that need to be considered in assessing the potential impacts of a conceivable nuclear conflict having regional or global extent.…”

“…There have been contrary assessments of the possible impacts of nuclear attacks on the global climate and environment. For example, most recently, a high-resolution modeling study ( 38 ) purported to demonstrate that a nuclear fire initiated by a 15-kt explosion in India or Pakistan would not loft enough smoke into the upper troposphere to contribute to widespread effects. However, that conclusion was based on a single simulation of such a detonation over a sparsely populated area about 8 km from the city center of Atlanta, Georgia.…”

Stratospheric pollution from Canadian forest fires

“…Self-lofting of this carbon (as demonstrated by the PNE) would raise it to an altitude where it would remain for a number of years, giving rise to the so-called nuclear winter [Robock et al (2007) and references therein]. Simulations (Reisner et al, 2018;Robock et al, 2007) of the response of the climate to a regional-scale nuclear war disagree on the severity of this effect. However, much of the disagreement is caused by widely different estimates of how much black carbon would reach the stratosphere from a given nuclear explosion.…”

Risk–Risk Tradeoff Analysis of Nuclear Explosives for Asteroid Deflection

“…Another study compares the crop data to existing poverty and malnourishment and estimates that the crop declines could threaten starvation for 2 billion people (Helfand, ). However, the aforementioned studies do not account for new nuclear explosion fire simulations that find approximately five times less particulate matter reaching the stratosphere, and correspondingly weaker global environmental effects (Reisner et al., ). Note also that the 100‐weapon scenario used in these studies is not the largest potential scenario.…”