Summary of Major Environmental Impacts of Nuclear Winter

Introduction: At EAG London last October, I met with Joan Rohlfing of the Nuclear Threat Initiative after her presentation on modern nuclear paradigms, and since then have been supported by her and other nuclear "enthusiasts" inside and outside of EA in undertaking this exploratory work on nuclear winter. (Including the Long-Term Future Fund, who are very supportive and understanding of half-formed ideas. If anyone out there is thinking of applying, you probably should.) Below is a largely unedited final draft of a research paper I wrote to explore the possibility of continuing a larger project along the same lines into different effects of nuclear winter. I think at this point I'm eager for [constructive] feedback, and hopefully to start conversations and/or encourage more people to do research on things that they feel passionate about. :)

Disclaimers: I am not a scientist; I am unfamiliar with atmospheric modelling (and modelling in general); I am usually a skeptic, but in the absence of any apparent reasonable ulterior motive beyond that of averting nuclear Armageddon, I am inclined to believe the scientists whose research I am relying on have faithfully represented their truest beliefs in their work, and conduct[ed] that work responsibly (especially Alan Robock - incredibly friendly guy). This research was conducted under the assumption that nuclear winter theory is largely correct; I did not find serious evidence otherwise in the course of my research, although that does not mean it doesn't exist. Simultaneously, I'm not invested in projecting personal objectivity.

Warning: It's depressing. 

Key Takeaways (according to me)

1. In the event of major nuclear catastrophe, human life would go on, and have the most luck doing it in the southern hemisphere. Human civilization would likely go on, but we're not sure how certain to be of that.
2. The toll on human life and in human suffering would be both immediate and drawn-out, involving up to a decade of climate effects and potentially thousands of years of nuclear pollution dispersed around the world (especially the northern hemisphere). Some of the longer-term effects that are spoken about least include the increased rates of cancer and radiation doses around the world, and deaths of despair, which I believe would not be insignificant.
3. There would be major environmental impediments to the maintenance and restoration of agriculture.
4. Many species would likely go extinct; an unknowable number of wild and domesticated animals would also die and suffer in the following ~five years.

Environmental Effects of Nuclear Conflict

I. Introduction

An international nuclear exchange, frankly, is probably not an X-risk, barring some kind of unforeseen circumstance like when they thought they might accidentally ignite the atmosphere. I'm willing to stand by the claim that it poses a risk of civilizational collapse in its worst forms, but honestly I'm much more concerned about the unequivocal reality that it would represent unimaginable human suffering on an unprecedented scale. The weapons are real, they already exist in the thousands, and they're held in the hands of chaotic actors who do not act in the best interests of humanity. As we all know we've come close to the brink a few too many times already. 

While it is impossible to be certain of the source of a catastrophic nuclear exchange before it happens [1], the sheer size of the global arsenal and the dangers posed to human civilization and to our Earth by nuclear weapons suggest the cruciality of military de-escalation. Experts are generally pessimistic about the likelihood of nuclear conflict, once initiated, to remain contained to specific areas [2,3]. Russia’s lax policies around nuclear risk and “crossing the nuclear threshold” by using smaller, “tactical” nuclear weapons have the potential to lead to tens of millions of deaths if met by similar aggression from NATO, [4]. More concerningly, the climatic effects of such a nuclear exchange have been studied more or less accurately for decades – and, through cascading environmental destruction, imply a risk to civilization itself [5]. 

II. The Atmosphere, Light, and Smoke

With the development of more powerful nuclear weapons came more concerning effects on our atmosphere. A 200-kiloton nuclear bomb, about 10 times as powerful as the “Fat Man” the US dropped on Nagasaki, would have most of the resulting dust, gas, and radioactivity washed out of the middle and upper troposphere within days to a month – a devastating environmental impact to be sure, but nothing compared to a megaton explosion. With a 1 megaton bomb, so far successfully constructed by the US, Russia, and China, this debris would be immediately carried into the stratosphere, where it would remain in our atmosphere potentially for years [6]. This is also possible, although less likely, with any nuclear yield greater than “a few hundred kilotons,” accomplishable by any nuclear power today [7]. 

The theory of nuclear winter arises from the temperature reduction resulting from massive clouds of smoke and dust produced by these explosions, as well as the smoke from combustion of cities, forests, crops, and fuel caused by the blasts [8]. Based on the 5 square mile ignition zone in Hiroshima, Greene estimates between 40 and 250 square miles of fire for every megaton exploded [9], with a reduction by up to 20% based on overlap in target area if the bombs are focused in Europe. Rates of combustion would range from encouragingly low during wet weather in natural areas to potentially near 100% in urban areas [10], making it difficult to reliably estimate smoke production from fires. Large petroleum storage and refining facilities, however, would likely be completely destroyed as strategic targets, greatly contributing to smoke, pollution, and potentially creating a fuel shortage [11]. If so, they might burn for months after ignition [12]. Confidence in contemporary estimations is supported by studies of volcanic eruptions, forest fires, and urban firestorms from conventional warfare [13], although these comparisons are likely to underestimate the magnitude of fires resulting from a nuclear blast due to the destruction of functional and effective urban firefighting services; in fact, for a variety of reasons, when past climate models have been found to be incorrect, they’ve largely been too optimistic [14].

Initially, given a sufficient amount of smoke, shown to be possible and likely in the event of a major summertime nuclear exchange, the amount of sunlight reaching the northern hemisphere could be reduced by up to 97% in places and up to 50% on average [15]. After initial days of near-total darkness at the areas of impact, this creates the low-light phenomenon of “twilight at noon,” as witnessed by victims of the Hiroshima and Nagasaki bombings [16]. While the density of the smoke clouds will decrease as they disperse across a greater area, Greene still estimates light levels similar to a “heavily overcast day, even at noon” anywhere in the Northern Hemisphere between the latitudes 30 and 70 degrees, “where most of the World’s population lives and where most of our crops are grown" [17]. Contrary to the primary danger of nuclear winter (cold temperatures), warming in the stratosphere from the injection of hot smoke would actually accelerate the spread to the Southern Hemisphere compared to average atmospheric winds, lowering temperatures across the world [18]. 

Urban fires as well as nuclear explosions also create nitrous oxides, which contribute to photochemical smog in the troposphere and lead to ozone destruction [19]. While the amount of light reaching Earth’s surface would drastically decrease, levels of UV radiation could actually double or even triple in areas underneath the ozone hole for prolonged periods of time [20]. Due to its connection with skin carcinoma, this extra UV radiation augments the added risk of cancer as a result of nuclear war [21]. Both UV radiation and radiation from fallout are known to suppress the immune system [22], a devastating compounding factor in the event of a resulting epidemic or pandemic, which is very likely in the aftermath of nuclear war given the absence of medical care and public sanitation following a nuclear blast [23]. UV-B radiation also puts the food supply at risk through reduced photosynthesis and decreased plant productivity in some crops [24] as well as damage to aquatic ecosystems [25].

III. Plants, Animals, and Agriculture

Over time, as the pollutants settle to the ground or are washed out of the atmosphere by precipitation, this puts water, soil, plants, and animals worldwide at risk of contamination from nuclear fallout and toxic chemicals produced by urban fires [26] (which would have also increased the death toll from the initial nuclear strike considerably, depending on how many cities were targeted) [27]. Some of these nuclear materials would likely never fully dissipate. Volcanic ash has been known to “poison the fields and water” temporarily, giving way after around a decade to a rebirth spurred on by its fertilizer-like effects [28]. – not so with elements like Cobalt-60, which theoretically could be weaponized to “salt the earth” with its 5-year half-life, or Plutonium-239, used in the bombing of Nagasaki, which can cause bone and lung tumors with its half-life of 24,400 years [29].

Of course, this is only a concern to plants not already dead from lack of sunlight or cold. The “twilight at noon” effect could continue over major crop-growing areas for up to two weeks or even two months. Growing plants and crops would essentially starve to death after only a fraction of this time [30]. Greene discusses the possible reversal of the greenhouse effect, as “thick clouds of smoke would stop most of the sunlight warming the Earth, but would allow most of the infrared radiation to escape,” leading to a massive reduction in average global temperature by up to 9 degrees Celsius on land and 3 degrees Celsius in the ocean [31]. Scientists have been less divided on the specific temperature variations than they are on humanity’s ability to recover from the world’s breadbasket latitudes losing anywhere between 10 and 40 degrees Celsius from their average temperature [32]. Wildfires and volcanic eruptions give us a good idea of the effects of tropospheric smoke; after Mt. St. Helen’s eruption, daytime temperatures beneath the smoke cloud dropped between 5-8 degrees Celsius [33]. However, it is crucial to note that depending on the size of the nuclear war, historic temperature variation due to volcanic eruption, which has caused slight global cooling and severe crop failure and famine, might reflect “less than one-twentieth of what might be expected" [34]. Volcanic eruptions also led to noticeable average temperature decreases for “only a few years" [35], but nuclear war is estimated to affect the global climate for between 6 and 10 years [36]. 

Temperature reductions pose a serious threat to crops and other plants for years after light levels have returned to near-normal. A decrease of even one degree Celsius could reduce average wheat production by half; two degrees is calculated to reduce production by up to 94%; at three degrees, wheat production is impossible [37]. Rice, soybean, and corn production would be reduced by 20% and remain decreased after a decade [38]. Workarounds such as planting later in the season or greater reliance on species of winter wheat are not useful due to continued low temperatures, although auto irrigation and additional fertilizer use would apparently reduce the impact of the nuclear war somewhat [39]. This is, however, not accounting for radioactive pollution of freshwater supplies and possible toxicity, for disruptions in supply chains which could inhibit the creation and transportation of that fertilizer, or for the expected mass deaths of pollinator species [40].

The ability of modern society to rely mostly on stored food until agriculture can be reorganized is contentious. In 1985, Greene estimated food stocks in an average town lasting 2-4 weeks, and government stores in most “developed Western countries” depleting within four months [41]. More optimistic estimates suggested that with total reallocation to human consumption, the U.S. population in 1985 could be fed a vegetarian diet relying on grain and beans for over two years – this is, however, not accounting for loss of stored food due to rodents, pests, or humidity; potential unavailability of processing plants or difficulty in transportation to said plants; or the logistic and political questions involved in the seizure and distribution of said food. Globally, tropical roots such as cassava and yams make up the staple diet of more than 600 million people, and yet are extremely vulnerable to decreases in temperature, which would likely come to pass in this scenario, leading to massive food loss [42]. Estimates for Chinese food security are similar to optimistic U.S. estimates – most likely exhausted within two years. Currently, up to 1/3 of the world’s food is lost or wasted, which would need to change immediately [43]. In the end, even if stored food is available, famine may not be averted if it is not accessible and affordable [44]. 

In the aftermath of the Tambora eruption, which ruined the following two harvests across the northern hemisphere, Behringer details the resulting famine in Bali and the surrounding islands. In Europe, “grapes threatened to freeze on the vines,” while in certain parts of China a greater reliance on finger millet countered some of the losses from diminished cultivation of sweet potatoes, maize, and peanuts, which only recovered after 1870, more than fifty years later. Rice harvests were only possible in the area around the volcano five years later [45]. This is consistent with Greene’s dire warnings of frozen crops and zero growth for at least a year [46]. Plant and crop regeneration is threatened by weeds and garden pests, as well as possible plant diseases and damage from UV radiation, fallout, and chemical pollution [47].

Unlike the destructive downpours after volcanic eruptions [48], plants would suffer from a lack of precipitation following a nuclear catastrophe. Turco estimated an average reduction in rainfall by up to 75% in the main northern grain-growing latitudes for the first few months following the attacks and up to 50% in seemingly unrelated areas like Australia for up to 1-3 years; multiple authors forecast the failure of the monsoon season in Asia, crucial for certain ecosystems and agricultural regimes [49]. Even though temperature fluctuations would be highest in temperate regions, smaller decreases in tropical regions could still lead to irreversible damage to rainforests, including the extinction of species unable to adapt [50]. The estimated effects of decreased oxygen production from forest fires and loss of plant life to deaths from fire and cold combined with increased atmospheric CO² are largely unknown [51]. The one blessing is that soil erosion would therefore be limited to that caused by the blast itself, as opposed to resulting rains as well [52]. On the other hand, hydroelectric power might suffer significantly from this decrease in average precipitation combined with the more frequent freezing temperatures [53].

Greene is concerned about the destruction of water supply systems and freezing of other water sources such as wells for drinking and sanitation. Of course, these supplies of potable water would likely also be dangerously polluted by radioactive fallout. Aside from the pollution that has washed out of the atmosphere directly into oceans and freshwater as acid rain [54], any erosion would also sweep radioactivity into rivers and coastal waters, since the rest would settle onto the top layer of soil [55]. Not only would people likely not realize the full extent of radioactive pollution, increasing individual doses of rads around the world, but it likely wouldn’t matter – water is a necessity, and lack of it kills faster than most doses of radiation [56]. The same would be true of marine food sources. The reduction in fish catch would be less than the reduction in land agriculture [57], but most fishing occurs around coastal waters, which would receive the radiation and toxins flushed in from rivers and thereby contaminate the fish, shrimp, and mollusks that make up significant portions of human protein consumption around the world to dangerous levels [58]. It is difficult to estimate the number of people who might be exposed to dangerous levels of radiation.

Outside of pollution, there will be significant deaths of phytoplankton and zooplankton in the Northern Hemisphere, in some areas potentially a majority of these populations would die off depending on the reduction in sunlight [59]. Even those which remain living would be unable to grow or reproduce as long as the twilight phenomenon continued. The fish and other marine animals that feed on these species would then go hungry and, in turn, likely fall in numbers significantly, especially in the event of a summer war when fat stores are lower [60]. All in all, ocean productivity could drop by up to 20% immediately and not restabilize for 6-9 years [61]. 

Traditional winter preparations might also save aquatic and terrestrial animals, but this would not be possible if the strikes were conducted outside of the Northern Hemisphere’s winter months. Even if they were, there is a chance of escalated rates of deaths from cold and starvation. Again, while the greatest differences would be noted in the temperate regions, tropical birds such as hummingbirds will die if the average air temperature drops by as little as 5 degrees Celsius, due to how easily they lose heat. The same is true for other birds and small mammals, as it is for small humans [62]. Small, weak, and old animals are likely to face extremely elevated death rates, particularly “specialized feeders such as insect-eating swifts, swallows, and bats” which would likely lose their only source of food [63]. Temperature reductions from the Tambora eruption saw “frozen birds [falling] from the trees” in New York. Bees and birds died across a variety of Pacific islands [64]. Even if they survived, 24-hour darkness would inhibit diurnal birds, predators, and pollinators which depend on sight, throwing ecosystems into chaos for weeks or months. Stressors are multiplicative: plants will receive more damage from UV radiation if they are struggling with cold; animals struggling with cold will do worse if they are also starving. Aside from volcanic eruptions, the closest comparison might be to the environmental catastrophes that contributed to the K-T extinction and the eradication of dinosaurs [65].

IV. Implications for Humanity

While nuclear winter does not clearly represent an extinction risk for humanity, it carries the immense weight of great human suffering, and a potential threat to human civilization. There is historical precedent in the Tambora Crisis for consecutive ruined harvests which threaten large portions of the Northern Hemisphere with food insecurity, having cascading effects into food exports to the Southern Hemisphere, and causing widespread famines. According to the Food and Agriculture Organization in 2013, roughly half of global calorie intake comes from cereals, which would be threatened globally by catastrophic nuclear exchange; 18% comes from meat and fish, fed by these grains and fostered by waters that would quickly become unsafe for consumption. China, on which most of the modern agricultural research into the effects of nuclear winter has been performed, is better positioned than most of the world in terms of food security to reestablish self-sufficiency and would potentially only suffer a 10% average caloric reduction; others, such as the estimated 805 million undernourished people in the world, would not be so lucky and would likely risk starvation [66]. 

The global agricultural system, one of Manheim’s three critical systems necessary for civilization, would face large scale vulnerability [67]. Most farm animals would suffer the same conditions as their wild counterparts, and Greene estimates 10% survival of animal stock in the face of hunger affecting all species and near-zero dairy production, while Xia looks to historical precedent in New England in 1815, the Year Without a Summer, to support her No Livestock scenario, where meat and animal product production, including aquaculture, breaks down after a year as crops are redirected towards human consumption [68]. 

Reestablishing food security was politically at the top of the list for the U.S. occupation of Japan after World War 2 to prevent civil unrest leading to greater chaos [69], but it’s unlikely in a large-scale nuclear winter scenario that there would be a nation in the position of the U.S. to distribute even what little food and medical aid they offered at the time. Political and social ramifications of this instability, including the potential for greater local and international violence, remain as of yet unstudied but would doubtlessly be significant. In the worst-case scenarios where most plant and animal life in the Northern Hemisphere is wiped out [70], we may see a breakdown in capacity for governance or rule of law, threatening the “trappings of civilization” itself [71], Greene suggests social fabric of civilization may “disintegrate” after the death of 50% of the population; Ord agrees with these estimates but suggests it would need to be the case in every region of the world, unless the global environment has been “damaged so severely that it has become impossible for the survivors to ever re-establish civilization" [72]. With 90% of the world’s population living in the Northern Hemisphere, which would be most affected by the climatic changes, including 25 out of the 31 “megacities” with over 10 million inhabitants [73], one could imagine human civilization continuing in the Southern Hemisphere even in the worst-case scenarios, but certainly with major crucial setbacks. 
 

Notes

[1] Dr. Alan Robock, source of “our current best understanding” of the risk posed by nuclear winter according to Toby Ord and others, focuses on estimates of climatological damage by nuclear war between India and Pakistan. Prof. Paul Bracken, who has been involved in conducting war games for the US Department of Defense, is now concerned by conflict with Russia, but moreso possible US conflict with Iran and/or North Korea. Importance of the exact warring nations for research into nuclear winter has been dismissed by experts including Robock, Bracken, and Xia “because soot disperses globally once it reaches the upper atmosphere” (“Global Famine”). 

[2] “The weight of the evidence indicates that, once started, a nuclear war between East and West is very likely to escalate to large-scale attacks… Once large-scale nuclear war begins, or appears inevitable, there would be intense pressure to launch most of the nuclear forces quickly. Otherwise they could be destroyed or isolated by enemy attacks.” (Greene 13); “Experts say that the war-fighting plans in general go from warning shots to single strikes to multiple retaliations and that the hardest question is whether there are reliable ways to prevent a conflict from escalating,” (Broad “The Smaller Bombs”); “The credibility of the United States with all of our alliances is that we would respond to a nuclear weapon with nuclear weapons. This would completely destroy NATO if we didn't fire back in kind” (Martin and Kaplan).

[3] Prof. Bracken indicated some expectation that conventional warfare could resume in place of further nuclear retaliation, but this is not reliably supported by the outcome of U.S. war games, half of which end with mutually assured destruction according to Martin and Kaplan. In addition, Bracken specified that the Pentagon has never pursued a study about most likely scenarios following nuclear weapons use; Dr. Shelly Lesher, Chair of the Physics Department at the University of Wisconsin–La Crosse and researcher of global nuclear issues, speculated that this is because the Pentagon lacks motivation to reveal the deadly and catastrophic outcomes of nuclear war. 

[4] “James R. Clapper Jr., a retired Air Force general who served as President Barack Obama’s director of national intelligence, said Moscow had lowered its bar for atomic use after the Cold War when the Russian army fell into disarray. Today, he added, Russia regards nuclear arms as utilitarian rather than unthinkable,” (Broad “The Smaller Bombs”). Broad also indicates Russia’s use of an “escalate to de-escalate” tactic in field exercises, involving “routed troops [firing] a nuclear weapon to stun an aggressor into retreat or submission.” Plan A’s scenario indicates that upon the initiation of a major nuclear exchange, we could expect 34.1 million immediate deaths and 57.4 million injuries, using NUKEMAP estimates. High mortality rates from injuries should be expected due to destruction of the local healthcare systems and transportation infrastructure. Dr. Robock’s estimates of war between India and Pakistan indicate between 50 and 125 million total deaths, depending on weapon yields. 

[5] “We are raising the very question of life on Earth,” (Yuri Izrael On the 8^th Day); “At a larger number [of nuclear weapons], civilisation’s ability to withstand the effects would be tested,” Baum. In the 90s, nuclear winter theory was reevaluated to hold a more optimistic position: not the total annihilation of the human race, only of civilization: ''My personal opinion is that the human race wouldn't become extinct, but civilization as we know it certainly would,” Dr. Richard Turco, “Nuclear Winter Theorists Pull Back.” Civilizational collapse is estimated to trigger at the destruction of around 50% of the human race (Greene 150; Ord 40). 

[6] Greene 3; 54. 

[7] Greene 29. 

[8] “[Sooty] smoke from urban fires is the major contributor to nuclear winter,” (Turco 166); quantity of smoke will determine the extent of nuclear winter, as calculated by 1) area burnt, 2) amount of fuel in this area, 3) fraction of fuel consumed by fire, and 4) proportion that becomes smoke (Greene 29) as well as “the nature of the flames, the temperature of burning, the oxygen supply, the wind conditions and the time since the fire started” (Greene 46); “probably the minimum of what may occur: wildfires in 10⁶ km² of forests, and the burning and escape of oil and natural gas at rates comparable to present industrial usage. The estimated atmospheric effects are very large. The fires would create sufficient quantities of airborne particulate matter in the atmosphere to screen out a large fraction of the solar radiation for many weeks, strongly reducing or even eliminating the possibility of growing agricultural crops over large areas of the Northern Hemisphere” (Crutzen & Birks 120). 

[9] San Francisco is about 47 square miles; the entirety of New York City is about 300 square miles.

[10] Greene 44; 30; 42. 

[11] Turco 168. 

[12] On the 8^th Day 23:45. 

[13] “The dust circled the Earth in three weeks” after a volcanic eruption, (On the 8^th Day 16:20); “Large parts of Asia suffered for months under a “dry fog” that obscured the sun. Upper winds distributed the gas and suspended particles around the world. The aerosols reduced solar radiation and led to a global cooling,” (Behringer 1); “The great forest fires during October 13-17, 1918 in Minnesota and adjacent sections of Wisconsin produced smoke that had strong optical effects and could even be smelled as far away as the eastern US coast,” (Crutzen & Birks 117); “Recent catastrophic forest fires in Canada in 2017-18 and Australia in 2019 and 2020 produced 0.3-1 Tg of smoke (0.006-0.02 Tg soot), which was subsequently heated by sunlight and lofted high in the stratosphere, adding confidence to nuclear war simulations that predict the same process will occur after nuclear war,” (Xia); during the bombing of Dresden, “the proportion of combustible material that was burnt was observed to be close to 100 per cent” (Greene 42). 

[14] Greene 24; “The power of the fires, however – along with the destruction of trucks and equipment and lack of water due to broken water mains and melted and damaged water pipes – prevented firefighters from containing the inferno,” (Southard 57); “Originally, we estimated that 25 to 50% of the smoke mass would be immediately scrubbed from urban fires by induced precipitation. However, based on current data, it is more reasonable to assume that, on average, 10 to 25% of the soot emission is likely to be removed in such a manner” (Turco 168); Robock, “Self-assured destruction”.

[15] Greene 46-7; “The average decreases in solar insolation over land from 300 to 70°N latitude are -40% with low amounts of smoke and -90% with high amounts of smoke (114, 115). At low latitudes (00 to 200N), the corresponding average light reductions are -0 to 50%, respectively” (Turco 172); “sufficient smoke could be generated during nuclear warfare to decrease average solar intensities by 50% or more on a hemispheric scale” (Turco 166). Turco also performs specific calculations about the light absorptivity of smoke (170). 

[16] “Under the cloud of smoke and dust, daylight could be reduced to near darkness for days and to twilight for weeks,” (Greene 4); 25% of the sun’s light is sent back to space by the dust in the stratosphere, reflecting; 74% is absorbed by soot in the troposphere and on the ground; only 1% reaches the Earth to warm it (26:45 On the 8th Day); ”It was still around noon…but the atomic cloud blocked the sun, so it was dark like night,” (Southard 55). 

[17] Greene 58-59. 

[18] Turco 166; “it may take a year or more for volcanic dust from a large volcanic explosion like Krakatoa in the Southern Hemisphere to reach Europe or America. But after a nuclear war, the circulation might be so changed, because of the heating of the clods of some dust by the Sun, that they could be carried across the equator and into the Southern hemisphere within a month or two. Computer calculations…tend to confirm this,” (Greene 60).

[19] Crutzen & Birks 115. 

[20] 100-200% increase in solar radiation in middle latitudes for a year or longer (Turco 173); Greene 4; 10-12 months after a nuclear attack (Greene 106); “the nitrogen oxides from the explosions and the fires could interact with the ozone in the stratosphere, destroying some of it and letting more of the dangerous ultraviolet radiation through to the surface of the Earth. The amount getting through could be more than doubled,” (Greene 71). 

[21] “Epidemiological data were used in the NAS study (I) to estimate that a 50 percent ozone shield reduction lasting three years would lead to an increase of skin carcinoma and melanoma of 3 percent to 30 percent at midlatitudes. with a geometric mean of about 10 percent, that will persist for 40 years. This may be compared with the estimate made in the same study that during the first generation a 10 000 Mt war would increase the spontaneous cancer death rate by about 2 percent as a result of exposure to low levels of ionizing radiation from radioactive fallout,” (Crutzen & Birks 123). 

[22] Greene 146; it also has the potential to damage the cornea and lead to blindness (Greene 115) along with radiation from certain atomic bombs. In Nagasaki, “cataracts, the clouding of the eyes’ crystalline lenses, were so frequently diagnosed that for a time they were called atomic bomb cataracts, caused by radiation damage to cells on the back surface of the lens” (Southard 176). 

[23] Greene 144-5; Robock “India-Pakistan nuclear war”; Southard 55; Jorgensen 158; other factors include risks posed by lack of sanitation leading to contaminated food and water and in turn food poisoning and diarrhea, potentially lethal to children and the elderly (Greene 147); the documented outbreaks of beriberi and tuberculosis during wartime in Japan (Ó Gráda) and other nutritional difficulties leading to the expedited spread of disease (Behringer 18, 45, 97, 103). 

[24] Crops such as peas and onions would have greater difficulty than others, such as corn and soybeans, in adjusting to greater UV radiation (Greene 107; Greene 109; Crutzen & Birks 123). However, given the significant decrease in sunlight along the world’s breadbasket latitudes, all major grain crops would be in danger to some degree. 

[25] “It was estimated from UV-B irradiation experiments that a 16 percent ozone reduction (the degree of ozone depletion projected by the NAS study for continued release of chlorofluoromethanes) could kill up to 50 percent of the anchovies in the top 10 meters of the clearest ocean water or else require them to substantially deepen their usual water depth. Avoidance could provide protection for many animals, but it is thought that few species can sense UV-B light” (Crutzen & Birks 123). Phytoplankton, the base of many aquatic food chains, are also very sensitive to UV radiation and could die off in massive numbers which would threaten the rest of their ecosystems (Greene 109). 

[26] “In a week or two, clouds of smoke and dust would spread around the Earth mainly in a zone from Texas in the south to the north of Norway. Then it would spread further to the north and south, possibly across the equator. In weeks or possibly months it would settle slowly to the ground,” (Greene 4); In the first 1-3 years, “The atmospheric residence time of the residual smoke is calculated to be ~1 year in these simulations. Moreover, after only 3 weeks the smoke is predicted to spread over the entire Northern Hemisphere and most of the Southern Hemisphere (from initial patches of injection over North America, Europe, and Western Asia),” Turco 173; “When burned, plastics generate a variety of toxic gases, including hydrogen chloride and hydrogen cyanide, that are environmentally hazardous,” (Turco 167). 

[27] In German shelters during World War II, most of the people who died after taking shelter died of carbon-monoxide poisoning rather than the fire itself (Greene 49); the thousands of deaths in Bhopal, India, as a result of a disastrous industrial gas leak of toxic methyl isocyanate in 1984 speaks to the disastrous effects of uncontrolled urban pollution (Greene 124). 

[28] Behringer 18-19. 

[29] Jorgensen 159. 

[30] “Net photosynthesis, and therefore growth and storage, is zero when light intensity falls to about 5-6 per cent of the noon value for a sunny June day… It could be darker than this for up to two weeks for our 6,000 megaton scenario and for up to two months for a more severe, 10,000 megaton scenario. So even if low light were the only problem, vegetation over much of the Northern Hemisphere would virtually stop growing and, in effect, starve for this period. Short-lived annual plants, which include all the major grain crops, would probably die. Trees and other perennials with greater food reserves might survive but they would be much weakened. They would be unlikely to form fruits or seeds, either because food reserves were too low or because the precise conditions of day length and temperature needed to flower were not met” (Greene 94-5). This is also consistent with experiments conducted for and reviewed by the On the 8^th Day documentary.

[31] Greene 61-2; 90; Robock “India-Pakistan nuclear war.”

[32] “average land cooling beneath the smoke clouds could reach 10 to 20°C and continental interiors could cool by up to 20 to 40°C with subzero temperatures possible even in summer;” (Turco 166); “Dr. Stephen H. Schneider of the National Center for Atmospheric Research in Boulder, Colo., a long-standing critic of the extreme nuclear winter hypothesis, believes that a cooling of 10 to 20 degrees centigrade (18 to 36 degrees Fahrenheit) would not constitute the arrival of ''winter.''” (Browne). 

[33] Greene 57; “Regional-scale smoke plumes generated by large forest fires have been observed to cause surface temperature decreases of several degrees Centigrade. Wildfires in Alberta, Canada, in 1982 were responsible for reducing the average daytime surface temperatures in the north-central United States by 1.50 to 4°C. More recently, the massive Chinese wildfires of May 1987 were found to reduce daytime temperatures over Alaska by 20 to 60C. In September 1987, a series of large wildfires erupted in southern Oregon and northern California. During one period, a dense smoke pall covered the Klamath River valley for 3 weeks. Recorded daytime temperatures were as much as 20°C below normal values. In all of these instances, the minimum nighttime temperatures were not significantly affected. The magnitude of the daytime cooling is consistent with theoretical expectations for the surface temperature effects of forest fire smoke [given its specific optical properties].” (Turco 171).

[34] Greene 64-5. 

[35] Crutzen & Birks 123.

[36] Greene 4; Xia; Robock “Self-assured destruction” and “India-Pakistan nuclear war.” 

[37] Greene 99, 139; Xia; Turco 172. 

[38] Robock “Self-assured destruction.”

[39] Except for spring wheat; Xia. 

[40] Xia; Greene 111. 

[41] Greene 132-133. Rural populations may store enough food to see a small family through a few extra months, if possible (135). 

[42] Greene 133-134; 136-7. 

[43] Xia. 

[44] Behringer 3. 

[45] Behringer 18, 42, 93, 16. 

[46] “Another point is that many important crop species grown in the temperate zone are of tropical origin – potatoes, tomatoes, cucumbers and maize, for example – and although the varieties used are more resistant to cold than the original tropical varieties, they still cannot withstand freezing of tissues and grow slowly, if at all, when severely chilled” (102); “Growth and food storage by plants could be zero for up to 10 months in the north temperate zone and for up to 6 months in the tropical zone, due mainly to shortage of light and reduced temperatures” (109-110). 

[47] Behringer 43; Greene 109-110.

[48] “A strange month because of the many cloudbursts and floods: because of the destructive hail and the cold when the sun was at its highest: all of this throughout southern Europe, from the 20th to the 30th parallel; and if I am not much mistaken, also reaching Asia and America at the same latitude,” “it began to rain at three o’clock in the morning on the 5th of May and continued without a moment’s interruption until the morning of the 10^th,” “The rains led to the flooding of rivers and lakes and to increasing soil instability. Roads became impassable, there were landslides and entire vineyards slid away. …In the middle of June, after torrential rains, several houses in Bamberg collapsed, burying fifteen people beneath them,” (Behringer 30). 

[49] Turco 172-3; Xia. 

[50] Greene 6.

[51] On the 8^th Day 53:00. 

[52] Greene 106. 

[53] Behringer 67. 

[54] Crutzen & Birks 120. 

[55] Greene 123. 

[56] Greene 132; “Nagasaki’s municipal water system was still in disrepair, so many people walked long distances to access working wells. An eight-year-old boy drank the water from a vase of flowers set at a gravesite. Two young girls retrieved water each day by crossing a school playground-turned-crematorium covered with ashes and fragments of human bone. Some people washed their clothes in the river as unclaimed decomposing corpses floated by,” (Southard 100). 

[57] Xia. 

[58] Greene 122, 125. 

[59] “If the production of aerosol by fires is large enough to cause reductions in the penetration of sunlight to ground level by a factor of a hundred…most of the phytoplankton and herbivorous zooplankton in more than half of the Northern Hemisphere oceans would die,” (Crutzen & Birks 120). 

[60] Greene 121. 

[61] Robock, “Self-assured destruction.” 

[62] Greene 131. 

[63] Greene 110-115. 

[64] Behringer 35; 15-6. 

[65] Greene 110, 93, 3. 

[66] Xia. 

[67] Manheim 4-5. 

[68] Greene 140; Xia. 

[69] Southard 140. 

[70] Greene 5. 

[71] Bostrom; Ord 40. 

[72] Greene 150; Ord 40; Ord 36. 

[73] “The World’s Cities in 2016,” United Nations, 2016, https://www.un.org/en/development/desa/population/publications/pdf/urbanization/the_worlds_cities_in_2016_data_booklet.pdf. 

Bibliography

Articles

Amano, M.A., et al. “Lifetime risk of suicide among survivors of the atomic bombings of Japan.” Epidemiology and Psychiatric Sciences, vol. 30, e43, Jun. 4, 2021. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8193967/.

Bostrom, Nick. “The Vulnerable World Hypothesis.” Global Policy, vol. 10, iss. 4, Nov. 2019, pp. 455-476. https://www.nickbostrom.com/papers/vulnerable.pdf.

Broad, William J. “How America Watches for a Nuclear Strike.” The New York Times, Apr. 5, 2022. 

Broad, William J. “The Smaller Bombs That Could Turn Ukraine Into a Nuclear War Zone.” The New York Times, Mar. 21, 2022. 

Browne, Malcolm W. “Nuclear Winter Theorists Pull Back.” The New York Times, Jan. 23, 1990. 

Begley, Sharon and Julie Steenhuysen. “How secure are labs handling world’s deadliest pathogens?” Reuters, Feb. 15, 2012. 

Cheng, Qu, et al. “Prenatal and early-life exposure to the Great Chinese Famine increased the risk of tuberculosis in adulthood across two generations.” PNAS, vol. 117, no. 44, 2020, pp. 27549–27555. https://www.pnas.org/doi/pdf/10.1073/pnas.2008336117.

Crutzen, Paul Jozef and John W Birks. “The Atmosphere after a Nuclear War: Twilight at Noon.” Ambio, vol. 11, no. 2-3, 1982, pp. 115-125. 

“Cuba: Going Against the Grain.” Oxfam America, 2001. https://www.oxfamamerica.org/explore/research-publications/cuba-going-against-the-grain/.

Kesternich, Iris, et al. “The Effects of World War II on Economic and Health Outcomes across Europe.” Review of Economics and Statistics, vol. 96, no. 1, 2014, pp. 103-118. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4025972/pdf/nihms461498.pdf.

Malus, Katherine. “Nuclear disaster: How prepared are we?” K=1 Project, Nov. 2, 2018. https://k1project.columbia.edu/content/nuclear-disaster-how-prepared-are-we.

Manheim, David. “The Fragile World Hypothesis: Complexity, Fragility, and Systemic Existential Risk.” Futures, vol. 122, 2020. https://www.sciencedirect.com/science/article/pii/S0016328720300604. 

Martin, Rachel. “The threat of nuclear war hangs over the Russia-Ukraine crisis.” NPR, Mar. 18, 2022. https://www.npr.org/2022/03/18/1087448484/the-threat-of-nuclear-war-hangs-over-the-russia-ukraine-crisis. 

Maponga, Tongai G., et al. “Persistent SARS-CoV-2 Infection with Accumulation of Mutations in a Patient with Poorly Controlled HIV Infection.” Preprint. https://papers.ssrn.com/sol3/papers.cfm?abstract_id=4014499. 

Ó Gráda, Cormac. “The famines of WWII.” VoxEU, Sep. 2, 2019. https://voxeu.org/article/famines-wwii. 

Robock, Alan, et al. “How an India-Pakistan nuclear war could start—and have global consequences.” Bulletin of the Atomic Scientists, vol. 75, no. 6, 2019, pp. 273-279. http://climate.envsci.rutgers.edu/pdf/IndiaPakistanBullAtomSci.pdf.

Robock, Alan and Owen Brian Toon. “Self-assured destruction: The climate impacts of nuclear war.” Bulletin of the Atomic Scientists, vol. 65, no. 5, 2012, pp. 66-74. https://journals.sagepub.com/doi/pdf/10.1177/0096340212459127.

Turco, R.P., et al. “Climate and Smoke: An Appraisal of Nuclear Winter.” Science, vol. 247, Jan. 12, 1990, pp. 166-176. https://atmos.uw.edu/~ackerman/Articles/Turco_Nuclear_Winter_90.pdf. 

Xia, Lili, et al. “Global Famine after Nuclear War.” Nature Food. Preprint. https://scholarworks.utrgv.edu/cgi/viewcontent.cgi?article=1152&context=eems_fac.

Books

Behringer, Wolfgang. Tambora and the Year Without a Summer: How a Volcano Plunged the World Into Crisis. New Jersey, John Wiley & Sons, 2019. 

Hare, Brian and Vanessa Woods. Survival of the Friendliest. New York, NY, Random House, 2020. 

Jorgensen, Timothy J. Strange Glow: The Story of Radiation. New Jersey, Princeton University Press, 2016. 

Ord, Toby. The Precipice: Existential Risk and the Future of Humanity. New York, NY, Hachette Books, 2020. 

Percival, Ian C., et al. Nuclear Winter: The Evidence and the Risks. Cambridge, UK, Polity Press, 1985. 

Southard, Susan. Nagasaki: Life After Nuclear War. New York, NY, Viking, 2016. 

Videos

"On the 8th Day – Nuclear Winter Documentary (1984)." YouTube, https://www.youtube.com/watch?v=WCTKcd2Ko98.

“PLAN A.” YouTube, Alex Glaser, https://www.youtube.com/watch?v=2jy3JU-ORpo&t=2s.