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Feature Bulletin of the Atomic Scientists 68(5) 66–74 ! The Author(s) 2012 Reprints and permissions: sagepub.co.uk/journalsPermissions.nav Self-assured destruction: DOI: 10.1177/0096340212459127 The climate impacts of http://thebulletin.sagepub.com nuclear war

Alan Robock and Owen Brian Toon

Abstract A nuclear war between Russia and the United States, even after the arsenal reductions planned under New START, could produce a nuclear winter. Hence, an attack by either side could be suicidal, resulting in self- assured destruction. Even a ÒsmallÓ nuclear war between India and Pakistan, with each country detonating 50 Hiroshima-size atom bombsÑonly about 0.03 percent of the global nuclear arsenalÕs explosive powerÑas air bursts in urban areas, could produce so much smoke that temperatures would fall below those of the Little Ice Age of the fourteenth to nineteenth centuries, shortening the growing season around the world and threaten- ing the global food supply. Furthermore, there would be massive ozone depletion, allowing more ultraviolet radiation to reach EarthÕs surface. Recent studies predict that agricultural production in parts of the United States and China would decline by about 20 percent for four years, and by 10 percent for a decade. The environmental threat posed by even a small number of nuclear weapons must be considered in nuclear policy deliberations. Military planners now treat the environmental effects as collateral damage, and treaties currently consider only the number of weapons needed to assure destruction of opposing forces. Instead, treaties must call for further reductions in weapons so that the collateral effects do not threaten the continued survival of the bulk of humanity. Proliferation cannot be treated as a regional problem. A regional conflict has the potential to cause mass starvation worldwide through environmental effects.

Keywords agriculture, climate, nuclear war, nuclear weapons, nuclear winter, ozone depletion, proliferation, smoke

n the early 1980s, as the arms race could produce so much smoke that it pushed the worldÕs total tally of would block out the sun, plunging the I nuclear weapons beyond 50,000, world into sub-freezing temperatures, nuclear winter changed everything. killing virtually all crops, and condemn- Scientists, including us, made the world ing the planet to mass starvation. aware of the environmental impacts of This shocking possibility, and the the smoke that would be generated by intense debate surrounding it, brought fires in cities and industrial areas in the the insanity of the continuing nuclear event of a nuclear war. A war between arms race to the front burner. The scien- the United States and the Soviet Union tific message, from research done jointly Robock and Toon 67 by American and Soviet scientists, was et al., 1983). Research in the past few based on primitive computer models of years has shown that SAD exists even the climate system, yet the physics were for the nuclear states with much smaller clear: If you block out enough sunlight, it arsenals: Britain, France, China, Israel, gets cold, dark, and dry at the surface, India, and Pakistan (Mills et al., 2008; and the destruction of the ozone layer Robock and Toon, 2010; Robock et al., allows deadly ultraviolet radiation to 2007b; Toon et al., 2007b). Yet policy penetrate the atmosphere. The scien- makers seem to be unaware of this situ- tistsÕ models motivated US President ation or are keeping it to themselves. Ronald Reagan and Soviet General When the policy implications of SAD Secretary Mikhail Gorbachev are considered, elementary planetary (Hertsgaard, 2000; Zubok, 2000) to hygiene demands a much more rapid reach agreement on a nuclear arms reduction in nuclear arsenals than cur- reduction treaty. rently planned, along with intensified The principle of mutually assured efforts to prevent further nuclear destruction (MAD) has presumably proliferation. been part of the reason that nuclear war has been avoided since those ter- Nuclear arsenals rible days in August 1945, when more than 250,000 residents of Hiroshima The total number of nuclear weapons and Nagasaki were incinerated by worldwide peaked at about 70,000 in nuclear explosions. MAD posits that, if 1986, when Reagan and Gorbachev country A attacks country B, the retali- agreed to reduce them (Figure 1). ation from country B will be so devastat- Currently, there are about 15,000 war- ing that a first strike would be suicidal heads (Norris and Kristensen, 2010). (e.g., Elkind, 2012). New START, signed by Presidents Nuclear winter theory tells us that it Barack Obama and Dmitry Medvedev would be suicidal for country A to in 2010, requires each side, within launch a full-scale nuclear attack on seven years of the treaty coming into country B regardless of whether country force, to reduce deployed warheads to B responds in kind. The resulting cli- a maximum of 1,550. However, each mate changes, triggered by smoke, long-range bomber counts as one war- would be so damaging to food and head no matter how many warheads it water supplies that infrastructure break- has, and the treaty does not limit the down would assure starvation in the much larger number of weapons that attacking country as well as the rest of are in storage or reserve. While the the world. Call it self-assured destruc- United States and Russia possess the tion, or SAD. bulk of the global nuclear arsenal, as of We now know that SAD has existed 2010 France had 300 nuclear weapons, since the 1950s. This was made explicit the United Kingdom had 225, China had in the 1980s by the first work showing 180, Pakistan had between 70 and 90, the potential for nuclear winter after a Israel and India each had between 60 war between the United States and and 80, and North Korea was thought Russia (Aleksandrov and Stenchikov, to have fewer than 10 nuclear weapons 1983; Robock, 1984, 1989; Turco (Norris and Kristensen, 2010). By 2012, 68 Bulletin of the Atomic Scientists 68(5)

Figure 1. A history of nuclear weapons

Source: Norris and Kristensen (2010) the arsenals of India and Pakistan had suggestions by a graduate student in pol- grown by an estimated 20 weapons itical science that the burning of forests each (Kristensen and Norris, 2011, 2012). and grasslands could cause changes in Studies of the effects of nuclear weap- continental weather (Lewis, 1979). We ons began soon after their invention. and our colleagues then discovered These studies were largely based on that smoke from urban fires posed an the military view that damage to speci- even greater global hazard in the form fied targets had to be assured to main- of climate anomalies, defined as a tain a deterrent. Hence, only the most Ònuclear winter,Ó capable of causing certain and quantifiable effectsÑsuch the worldwide collapse of agriculture as blast and prompt radiationÑwere (Aleksandrov and Stenchikov, 1983; considered. Robock, 1984; Turco et al., 1983). A nuclear war would also threaten much Nuclear winter of the worldÕs population by causing societal chaos and the loss of transpor- That changed in 1982, when the journal tation and energy production. of the Royal Swedish Academy of Modern climate models not only Sciences, Ambio, published a ground- show that the nuclear winter theory is breaking article (Crutzen and Birks, correct, but also that the effects would 1982) that identified the issue of smoke last for more than a decade (Robock generated by nuclear-ignited forest fires et al., 2007a, 2007b) because of an unex- as a global concern, following earlier pected phenomenon: Smoke would rise Robock and Toon 69

Figure 2. Global precipitation and temperature changes as a function of smoke emitted

Sources: Robock et al. (2007a, 2007b); Toon et al. (2008) to very high altitudesÑnear 40 kilo- within the range of arsenals planned meters (25 miles)Ñwhere it would be for the coming decade (Toon et al., protected from rain and would take 2008). For instance, the use of 4,000 more than a decade to clear completely. weapons (the rough total for US and As a consequence, the smokeÕs climate Russian arsenals in 2017 under New impacts would be more extreme than START), each with a yield of 100 kilo- once thought. For example, the new tons (a typical yield for submarine models show that a full-scale nuclear weapons, but at the low end for conflict, in which 150 million tons of most nuclear weapons), against urban smoke are lofted into the upper atmos- or industrial targets would produce phere, would drastically reduce precipi- about 180 million tons of soot. A single tation by 45 percent on a global average, US submarine carrying 144 weapons of while temperatures would fall for sev- 100-kiloton yield could produce 23 mil- eral years by 7 to 8 degrees Celsius on lion tons of smoke if these weapons were average and would remain depressed by used on densely populated Chinese 4 degrees Celsius after a decade (Robock cities. et al., 2007a). Humans have not experi- enced temperatures this low since the Regional nuclear war last ice age (Figure 2). In important grain-growing regions of the northern The United States and Russia are not the mid-latitudes, precipitation would only countries capable of wreaking decline by up to 90 percent, and tem- worldwide climate havoc. All of the peratures would fall below freezing and nuclear statesÑexcept North Korea, remain there for one or more years. with its relatively small arsenalÑif The number of weapons needed to involved in a nuclear war, have the initiate these climate changes falls destructive power needed to alter the 70 Bulletin of the Atomic Scientists 68(5) global environment (Robock et al., over the mid-latitudes of both hemi- 2007b). spheres would be reduced to values It is not correct to assume that the now found only in the Antarctic ozone effects of a regional war would be con- hole (Mills et al., 2008). tained within a limited zone. For exam- ple, consider a nuclear war in South Asia Policy implications involving the use of 100 Hiroshima-size weapons. In these simulations, more These global climate effects could result than five million tons of smoke is lofted from a nuclear attack by one country on to high altitude, where it absorbs sun- another, with no nuclear retaliation: self- light before the light can reach the assured destruction. For example, it is lower atmosphere (Toon et al., 2007b). possible that an Israeli nuclear attack As a result, surface temperatures fall and on Iranian population centers and indus- precipitation declines (Robock et al., trial areas could do this, although further 2007b). The calculated results show a research is needed to confirm that pos- 10 percent global drop in precipitation, sibility. Yet the worldÕs nuclear policy with the largest losses in the low lati- makers do not consider these effects in tudes due to failure of the monsoons. their plans and policies, nor are they Our climate model also shows global conducting research to better under- average temperatures colder than any stand them. experienced on Earth in the past 1,000 Even the direct fatalities caused by a years and growing seasons shortened nuclear attack have been under- by two to three weeks in the main mid- appreciated (Toon et al., 2007a). In latitude agricultural areas of both hemi- most cases, we find that just one nuclear spheres. These effects persist for several explosion with a Hiroshima-size weapon years, which would threaten a signifi- can lead to 100 times as many deaths in a cant fraction of the worldÕs food country that is attacked as in many pre- supply, perhaps jeopardizing a billion vious conventional conflicts (Toon people who are now only marginally et al., 2007b). Just a few nuclear explo- fed as it is (Helfand, 2012). New simula- sions could result in more fatalities than tions of the effects of these climate most countries experienced in World changes on crop production predict War II. For example, although North reductions of soybean and corn produc- Korea does not have enough weapons tion in the US Midwest, and of rice pro- to produce global climate effects, if it duction in China, of 20 percent for were to explode just three Hiroshima- several years and 10 percent even after size nuclear weapons in US cities, the a decade (O¬zdogùan et al., 2012; Xia and United States could experience as Robock, 2012). many fatalities as it did during all of These impacts could be felt even in a World War II, about 420,000. A full- warming world. Imagine the disruption scale war between India and in world food trade with such heavy PakistanÑas another exampleÑcould losses of production. The smoke would kill tens of millions of people, about also heat the upper atmosphere by as one-third as many as died in World much as 50 degrees Celsius for several War II globally. Indeed, nuclear years. As a consequence, ozone levels weapon states capable of deploying Robock and Toon 71 about 100 weapons globally could cause these issues. Research conducted jointly as many fatalities through the direct by scientists from all of the nuclear effects of the explosions as the Soviet nations, as occurred when American Union was once forecast to be capable and Soviet scientists did the original of inflicting on the United States during nuclear winter work in the 1980s, a full counterforce war. Hence, each of would be a powerful message to the the nuclear weapon states except North world about the seriousness of these Korea, which only has about 10 weapons, problems. must be considered as dangerous as the Cold War adversaries of the previous Arms control treaties century, as soon as they develop long- range missiles. India has just demon- India, Pakistan, and North Korea often strated that capability, and clearly Iran defend their development of arsenals (which is not believed to have any by pointing to the larger caches held by nuclear weapons yet) and North Korea the dominant nuclear weapons states. (which is interested in increasing its The United States and Russia have arsenal) are working hard to build and deployed arsenals that will be reduced test long-range, nuclear-capable to about 6 percent of their peak levels missiles. by 2017. But these arsenals are substan- There are many aspects of a putative tially overbuilt for the mission of deter- future war that are fundamentally rence and if ever used might destroy unpredictable, particularly the targets human civilization. that would be attacked, as well as the Nuclear arms control treaties are numbers and sizes of weapons that based on systematic, counter-balanced would be used. There are also many build-downs of nuclear weapons. technical issues that need additional However, the treaties are not based on study, including a more detailed analysis an analysis of the reductions needed to of the amount and properties of smoke ensure that the human race is not threa- that would emanate from various targets tened with unintended mass annihila- when attacked by various sizes of weap- tion. The majority of fatalities would ons. Other climate models should repeat probably occur through global environ- the calculations of climate impacts to mental damage and through destruction make sure they are robust. The impacts of the global infrastructure supporting on different crops in different parts of transportation, agriculture, and social the world, as well as on water resources, order. deserve further study. Yet funding for Article VI of the Nuclear Non- this research is currently lacking. Proliferation Treaty calls on all signa- Neither the US Defense Department, tory states Òto pursue negotiations in which possesses and might use nuclear good faith on effective measures relating weapons, the US Energy Department, to cessation of the nuclear arms race at which manufactures these weapons, an early date and to nuclear disarma- nor the US Homeland Security ment, and on a treaty on general and Department, which is responsible for complete disarmament under strict and dealing with the climatic effects of effective international control.Ó It is nuclear war, is conducting research on time for the world to find political 72 Bulletin of the Atomic Scientists 68(5) leaders with the courage to take action as Pakistan tried to do soon after testing to comply with this long-standing its first weapon. It is now time to add agreement. self-assured destruction to the list of A rapid reduction of the US and reasons for ridding the world of nuclear Russian arsenals to about 200 weapons weapons. each, and an immediate agreement to We have published many articles not target cities and industrial areas, about our research and given multiple would allow both countries to maintain presentations about it to scientists, con- their nuclear deterrence and would pre- gressional staff, and nongovernmental vent the possibility of killing the major- organizations. But with the exception ity of humanity through nuclear winter, of Switzerland, not a single country has although significant environmental asked its scientists to evaluate the threat damageÑperhaps killing a billion posed to its citizens by a nuclear conflict people in a nuclear famine (Helfand, within its borders or on the other side of 2012)Ñcould still result from nuclear the world (Robock, 2011). conflict. Such a reduction would also In response to our latest work on agri- set an example for other countries con- cultural impacts, Mikhail Gorbachev sidering the development of nuclear said: ÒI am convinced that nuclear weap- weapons. Negotiations with all other ons must be abolished. Their use in a nuclear nations for rapid reductions of military conflict is unthinkable; using their arsenals would then reduce the them to achieve political objectives is continued environmental threat of the immoral. Over 25 years ago, President remaining weapons. Ronald Reagan and I ended our summit meeting in Geneva with a joint state- Action needed now ment that ÔNuclear war cannot be won and must never be fought,Õ and this The push to abolish nuclear weapons new study underscores in stunning and has gained momentum over the past disturbing detail why this is the caseÓ few years. For example, the ÒGang of (Dhanapala and Helfand, 2012). It is FourÓÑGeorge P. Shultz, William J. time once more for the world to listen Perry, Henry A. Kissinger, and Sam to Gorbachev. NunnÑhave published a series of four op-eds in the Wall Street Journal arguing Acknowledgements that MAD can no longer work in a world The authors thank Martin Bunzl for valuable with so many nuclear nations (Shultz comments. et al., 2007, 2008, 2010, 2011). The Global Zero campaign and Scott D. Funding Sagan, in calling for global nuclear dis- Alan Robock is supported by National Science armament, make no reference to the cli- Foundation grants atm-0730452 and ags-1157525. matic effects of nuclear weapons but advance additional valid arguments. References For example, Sagan (2012) points out Aleksandrov VV and Stenchikov GL (1983) On the that, in the future, nuclear weapons modeling of the climatic consequences of nuclear war. Proceeding on Applied Mathematics, 21. may be used as a shield to allow conven- Moscow: Computing Centre of the USSR tional wars to be fought with impunity, Academy of Sciences. Robock and Toon 73

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Author biographies Sciences, and a research associate at the Alan Robock is a distinguished professor in Laboratory for Atmospheric and Space the Department of Environmental Sciences, Physics, at the University of Colorado, and the associate director of the Center for Boulder. He leads a research group that studies Environmental Prediction, at Rutgers aerosols and cloud physics, and investigates University. Previously, he was a faculty climate and atmospheric chemistry on Earth member of the Department of Meteorology at and other planetary bodies. the University of Maryland and the state cli- matologist of Maryland. He researches the cli- Both authors have been involved in nuclear matic effects of nuclear weapons, the effects of winter research since the early 1980s. More volcanic eruptions on climate, geoengineering, information about their work on the climatic and soil moisture. consequences of nuclear conflictÑincluding images, presentations, and papersÑis Owen Brian Toon is a professor in the available at http://climate.envsci.rutgers.edu/ Department of Atmospheric and Oceanic nuclear/.