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

Abstract

Here, we use a coupled atmospheric-ocean-aerosol model to investigate the plume development and climate effects of the smoke generated by fires following a regional nuclear war between emerging third-world nuclear powers. We simulate a standard scenario where 5 Tg of black carbon (BC) is emitted over 1 day in the upper troposphere-lower stratosphere. However, it is likely that the emissions from the fires ignited by bomb detonations include a substantial amount of particulate organic matter (POM) and that they last more than 1 day. We therefore test the sensitivity of the aerosol plume and climate system to the BC/POM ratio (1:3, 1:9) and to the emission length (1 day, 1 week, 1 month). We find that in general, an emission length of 1 month substantially reduces the cooling compared to the 1-day case, whereas taking into account POM emissions notably increases the cooling and the reduction of precipitation associated with the nuclear war during the first year following the detonation. Accounting for POM emissions increases the particle size in the short-emission-length scenarios (1 day/1 week), reducing the residence time of the injected particle. While the initial cooling is more intense when including POM emission, the long-lasting effects, while still large, may be less extreme compared to the BC-only case. Our study highlights that the emission altitude reached by the plume is sensitive to both the particle type emitted by the fires and the emission duration. Consequently, the climate effects of a nuclear war are strongly dependent on these parameters.

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

“…Our primary result is the decreased impact on global climate indices, such as global average surface temperature and precipitation, relative to standard scenarios considered in previous work (e.g., Mills et al, 2014;Pausata et al, 2016;Stenke et al, 2013). With our finding of substantially less BC aerosol being lofted to stratospheric heights (e.g., over a factor of 4 less than in most of the scenarios considered by previous studies), these globally averaged anomalies drop to statistically insignificant levels after the first several years (Figures 14 and 16).…”

“…and 150 hPa (i.e., in the upper troposphere, roughly between 9 and 14 km), with a constant mass-mixing ratio, over two regions centered on India and Pakistan. A similar initial distribution for the BC was used, among others, by , Mills et al (2008), Stenke et al (2013), and Pausata et al (2016). With this simulation setup, the observed climatic effects are largely similar to those discussed by Mills et al (2014), although they conducted most of their experiments with 50 nm radius BC particles.…”

“…Likewise, recent work in analyzing BC emissions from large fires suggests that in such fires, similar to large volcanic eruptions, coating of soot particles with other particles in convective eddies tends to increase their size and hence increase their subsequent rainout (China et al, ) before they can reach the stratosphere. In fact, the recent study of Pausata et al () found that growth of BC aerosol via coagulation with organic carbon significantly reduces the particles' lifetime in the atmosphere.…”

A regional nuclear conflict would compromise global food security

“…Climatic responses to large soot injections over South Asia have been studied systematically (8,(13)(14)(15)(16)(17). The impacts of such low-likelihood but severe events require careful investigation to inform the public and policy makers in view of nuclear proliferation and conflict.…”

“…The season and geographic location of soot emissions could influence soot production, rainout, and lofting, yet a systematic evaluation is lacking (6,15). The size of the conflict, fuel load, smoke composition, and plume rise introduce additional uncertainties (6,8,15,17,31,47,48). Recently revised estimates of combustible material with today's larger nuclear arsenals render previous assumptions of 5 Tg soot conservative and suggest that soot production may range from 5 to 36 Tg for the India-Pakistan case (13).…”