Opinion: How fear of nuclear winter has helped save the world, so far

Opinion Atmos. Chem. Phys., 23, 6691–6701, 2023 https://doi.org/10.5194/acp-23-6691-2023 © Author(s) 2023. This work is distributed under the Creative Commons Attribution 4.0 License. Opinion: How fear of nuclear winter has helped save the world, so far Alan Robock1, Lili Xia1, Cheryl S. Harrison2, Joshua Coupe5,a, Owen B. Toon3, and Charles G. Bardeen4 1Department of Environmental Sciences, Rutgers University, 14 College Farm Road, New Brunswick, New Jersey 08901, USA 2Department of Ocean and Coastal Science and Center for Computation and Technology, Louisiana State University, Baton Rouge, Louisiana 70803, USA 3Department of Atmospheric and Oceanic Sciences, Laboratory for Atmospheric and Space Physics, University of Colorado, Boulder, Colorado 80303, USA 4Atmospheric Chemistry Observations and Modeling Laboratory, National Center for Atmospheric Research, Boulder, Colorado 80307, USA 5Institute of Arctic and Alpine Research, University of Colorado, Boulder, Colorado 80309, USA aDepartment of Atmospheric and Oceanic Sciences, University of Colorado, Boulder, Colorado 80309, USA Correspondence: Alan Robock (robock@envsci.rutgers.edu) Received: 22 December 2022 – Discussion started

6692 A. Robock et al.: How fear of nuclear winter has helped save the world, so far Stenchikov (1983) were the first to use a three-dimensional general circulation model (GCM), and they also found that there would be nuclear winter over the land even though the model included the effects of oceans. This new research showed that there could be global impacts of nuclear war far from the target areas and nations involved in the war. While the direct effects of a nuclear war might kill hundreds of millions in combat zones, the indirect effects could lead to collapse of world agriculture and starvation of billions of people even in regions that were not involved directly in the war. The basic science of nuclear winter is not complicated. If nuclear weapons were exploded on cities and industrial areas, probable targets of nations with those weapons, they would start fires, producing massive amounts of smoke, some of which would end up in the stratosphere. That smoke would block out sunlight, making it cold, dark, and dry at the surface for many years, as well as heat the stratosphere, destroying ozone and producing enhanced ultraviolet radiation at the surface after a sufficient amount of s

A. Robock et al.: How fear of nuclear winter has helped save the world, so far 6693 The basic conclusion that a large-scale nuclear conflict would have devastating climatic consequences was not only supported but also strengthened. Using simple scenarios of 50 and 150 Tg of soot injected into the upper troposphere, Robock et al. (2007a) found that indeed the 150 Tg scenario, with an injection of soot which is still possible from the use of the current US and Russian nuclear arsenals (Toon et al., 2008), would produce a nuclear winter. And they found that the climate effects would last for more than a decade, as for the first time they were able to realistically simulate the lifetime of the soot particles in the upper atmosphere. Coupe et al. (2019) repeated these experiments using the Community Earth System Model-Whole Atmosphere Community Climate Model version 4 (WACCM4; Marsh et al., 2013; Bardeen et al., 2017), run at 1.9° × 2.5° horizontal resolution with 66 layers from the surface to 140 km, with full stratospheric chemistry and with the Community Aerosol and Radiation Model for Atmospheres in the stratosphere allowing particle growth (Toon et al., 1988; Turco et al., 1979; Bard

6694 A. Robock et al.: How fear of nuclear winter has helped save the world, so far Figure 1. Time series of the total number of nuclear weapons on Earth, which after about 2005 excludes large numbers of tactical nuclear weapons as well as weapons in storage waiting to be dis- three international conferences on the humanitarian impacts of nuclear war – in Oslo, Norway (2–3 March 2013); Nayarit, Mexico (13–14 February 2014); and Vienna, Austria mantled. The total includes all nine nuclear-weapon states, but the (8–9 December 2014) – as governmental expert conferences. other seven have at most a few hundred each (Kristensen and Norris, ICAN and other non-governmental organizations as well as 2015), updated 2023 from Bulletin of the Atomic Scientists (2023). and Space Administration/Goddard Institute for Space Studies ModelE GCM, they calculated global average cooling of more than 1 K, to a temperature colder than ever before experienced in recorded human history. This was the first time an atmosphere–ocean GCM had been used for this problem, and it was one that had a complete stratosphere and mesosphere, allowing calculation of the lofting of the smoke by solar heating and its global

A. Robock et al.: How fear of nuclear winter has helped save the world, so far 6695 trol over such weapons or explosive devices directly or indirectly; (c) Receive the transfer of or control over nuclear weapons or other nuclear explosive devices directly or indirectly; (d) Use or threaten to use nuclear weapons or other nuclear explosive devices; (e) Assist, encourage or induce, in any way, anyone to engage in any activity prohibited to a State Party under this Treaty; (f) Seek or receive any assistance, in any way, from anyone to engage in any activity prohibited to a State Party under this Treaty; (g) Allow any stationing, installation or deployment of any nuclear weapons or other nuclear explosive devices in its territory or at any place under its jurisdiction or control. Unfortunately, the nine nuclear states have not yet ratified the treaty and have encouraged their allies to ignore it. But 7 Global famine, ultraviolet radiation, and extended oceanic response While elated that our work helped lead to a treaty to ban nuclear weapons and to a Nobel Peace Prize, we still have many scientific questions to address, including several details of the amounts of fuel in target areas, th

6696 A. Robock et al.: How fear of nuclear winter has helped save the world, so far Table 1. Number of weapons on urban targets, yields, direct fatalities from the bomb blasts, and resulting number of people in danger of death due to famine for the different scenarios we studied. The 5 Tg case scenario is from Toon et al. (2007) for an India–Pakistan war taking place in 2008; the 16–47 Tg cases are from Toon et al. (2019) for an India–Pakistan war taking place in 2025; and the 150 Tg case is from Coupe et al. (2019), which assumes attacks on France, Germany, Japan, UK, USA, Russia, and China. The last column is the number of people who would starve by the end of year 2 when the rest of the population is provided with the minimum amount of food needed to survive, assumed to be a global average calorie intake of 1911 kcal per capita per day, and for no international trade, for a case in which 50 % of livestock crop feed was used for human consumption, and 50 % of livestock crop feed was used to raise livestock, using the latest complete data available, for the year 2010. For 2010, the total population of the nations used in the study was 6 700 000 000. There are many other scenarios

A. Robock et al.: How fear of nuclear winter has helped save the world, so far 6697 Figure 3. As described by Xia et al. (2022), we assumed that all stored food would be consumed within months after a nuclear war and calculated for the next year how many people would survive in each country if there was no international trade, if all people ate the minimum number of calories needed to support regular physical activity, and that once the available food ran out no food would be given to the fraction of the population that is predicted to die. That portion is plotted on this map for a 37 Tg soot injection, assuming that half the livestock was maintained, and the livestock crop feed that would have gone to the rest would go to humans. This would result in the death of 1–2 billion people. Of course, the fraction of the population given no food would likely attack those with food, leading to even more deaths. ating a famine in the ocean, with higher impacts to marine food sources in the Northern Hemisphere and coastal regions worldwide. In the larger war scenarios, this would pose intense limitations on fishing. Realistic adaptation measures we studied, such as reducing livestock producti

6698 A. Robock et al.: How fear of nuclear winter has helped save the world, so far Figure 5. Postwar Arctic sea ice evolution. Arctic 2020–2025 mean sea ice concentration (%) for (a) the USA–Russia nuclear war (NW) scenario, (b) the control scenario, and (c) the difference in concentration between the two scenarios. Arctic mean sea ice thickness (m) for (e) the USA–Russia nuclear war scenario, (f) the control scenario, and (g) the difference in thickness between the two scenarios. The Northern Hemisphere annual mean time series of (d) sea ice extent and (h) sea ice volume is shown for all war scenarios (colors) and control scenarios (black), where the Community Earth System Model-Large Ensemble (CESM-LE) experiment mean (solid grey line) and standard deviation (dashed) over the preindustrial period are given to demonstrate the natural, internal variability within the model (Fig. 5 from Harrison et al., 2022). sea ice in the first years after the war when food shortages would be highest, affecting shipping in regions into crucial ports where sea ice is not currently experienced, such as the Yellow Sea. This is illustrated in Fig. 5. In all scenarios, the ocean would cool rapidly but

A. Robock et al.: How fear of nuclear winter has helped save the world, so far 6699 on a treaty on general and complete disarmament under strict and effective international control.” On 27 October 2022, Pakistan’s ambassador to the United States, Masood Khan, warned of a nuclear winter that could result from escalation of conflicts in Kashmir between nuclear-armed Pakistan and India (O’Connor, 2022). The 16 November 2022 G20 Bali Leaders’ Declaration indirectly refers to nuclear winter, and included the following: It is essential to uphold international law and the multilateral system that safeguards peace and stability. This includes defending all the Purposes and Principles enshrined in the Charter of the United Nations and adhering to international humanitarian law, including the protection of civilians and infrastructure in armed conflicts. The use or threat of use of nuclear weapons is inadmissible. But if the nuclear weapons states claim that the only reason they keep their nuclear weapons is for deterrence, that involves the threat of their use of nuclear weapons. So there is more work to do. Several of us, Alan Robock, Brian Toon, Rich Turco, and Gera Stenchikov, received the

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