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Nuclear winter (also known as atomic winter) is a hypothetical climatic effect of countervalue nuclear war. Models suggest that detonating dozens or more nuclear weapons on cities prone to firestorm, comparable to the Hiroshima city of 1945, could have a profound and severe effect on the climate causing cold weather and reduced sunlight for a period of months or even years by the emission of large amounts of the firestorms smoke and soot into the Earth's stratosphere.
Similar climatic effects are believed to have followed large comet and asteroid impacts in the past, due to sulfate bearing rock being pulverized and lofted high into the air combined with the ignition of multiple forest firestorms, which is sometimes termed an impact winter, and following a supervolcano eruption, pluming sulfate aerosols high into the stratosphere, known as a volcanic winter.
The nuclear winter scenario assumes that if 100 or more city firestorms follow the nuclear explosions of a nuclear war, and the firestorms loft large enough amounts of sooty smoke into the upper troposphere and lower stratosphere, soot lifted by the movement offered by the pyrocumulonimbus clouds that form during a firestorm. At 10–15 kilometres (6–9 miles) above the Earth's surface, the absorption of sunlight could further heat the smoke, lifting some, or all of it, into the stratosphere, where the smoke could persist for years, if there is no rain to wash it out. This aerosol of particles could block out much of the sun's light from reaching the surface, with this causing surface temperatures to drop drastically, and with that, it is predicted surface air temperatures would be akin to, or colder than, a given region's winter, for years on end.
The exact timescale for how long this smoke remains, and thus how severely this smoke affects the climate once it reaches the stratosphere, is dependent on both chemical and physical removal processes.
The physical removal mechanisms affecting the timescale of smoke particle removal are how quickly the aerosol particles coagulate, and fall out of the atmosphere via dry deposition, and to a slower degree, the time it takes for solar radiation pressure to move the particles to a lower level in the atmosphere. Whether by coagulation or radiation pressure, once the aerosol of smoke particles are at this lower atmospheric level cloud seeding can begin, permitting precipitation to wash the smoke aerosol out of the atmosphere by the wet deposition mechanism.
The chemical processes that affect the removal are dependent on the ability of atmospheric chemistry to oxidize the smoke, via reactions with oxidative species such as ozone and nitrogen oxides, both of which are found at all levels of the atmosphere. Historical data on residence times of aerosols, albeit a different mixture of aerosols, in this case stratospheric sulfur aerosols and volcanic ash, from megavolcano eruptions, appear to be in the 1-2 year time scale.
A study presented at the annual meeting of the American Geophysical Union in December 2006 found that even a small-scale, regional nuclear war could disrupt the global climate for a decade or more. In a regional nuclear conflict scenario where two opposing nations in the subtropics would each use 50 Hiroshima-sized nuclear weapons (about 15 kiloton each) on major populated centres, the researchers estimated as much as five million tons of soot would be released, which would produce a cooling of several degrees over large areas of North America and Eurasia, including most of the grain-growing regions. The cooling would last for years, and according to the research could be "catastrophic".
A 2008 study published in the Proceedings of the National Academy of Science found that a nuclear weapons exchange between Pakistan and India using their current arsenals could create a near-global ozone hole, triggering human health problems and causing environmental damage for at least a decade. The computer-modeling study looked at a nuclear war between the two countries involving 50 Hiroshima-sized nuclear devices on each side, producing massive urban fires and lofting as much as five million metric tons of soot about 50 miles (80 km) into the mesosphere. The soot would absorb enough solar radiation to heat surrounding gases, causing a series of chemical reactions that would break down the stratospheric ozone layer protecting Earth from harmful ultraviolet radiation.
A "nuclear summer" is a hypothesized scenario in which, after a nuclear winter has abated, a greenhouse effect then occurs due to CO2 released by combustion and methane released from decay of dead organic matter.
Based on new work published in 2007 and 2008 by some of the authors of the original studies, several new hypotheses have been put forth. However far from being "new", the very same "threshold" to nuclear winter effects was similarly regarded in the mid 1980s to have been about a total of 100 or so city firestorms.
A minor nuclear war with each country using 50 Hiroshima-sized atom bombs as airbursts on urban areas could produce climate change unprecedented in recorded human history. A nuclear war between the United States and Russia today could produce nuclear winter, with temperatures plunging below freezing in the summer in major agricultural regions, threatening the food supply for most of the planet. The climatic effects of the smoke from burning cities and industrial areas would last for several years, much longer than previously thought. New climate model simulations, which are said to have the capability of including the entire atmosphere and oceans, show that the smoke would be lofted by solar heating to the upper stratosphere, where it would remain for years.
Compared to climate change for the past millennium, even the smallest exchange modeled would plunge the planet into temperatures colder than the Little Ice Age (the period of history between approximately A.D. 1600 and A.D. 1850). This would take effect instantly, and agriculture would be severely threatened. Larger amounts of smoke would produce larger climate changes, and for the 150 teragrams (Tg) case produce a true nuclear winter (1 Tg is 1012 grams), making agriculture impossible for years. In both cases, new climate model simulations show that the effects would last for more than a decade.
A study published in the Journal of Geophysical Research in July 2007, "Nuclear winter revisited with a modern climate model and current nuclear arsenals: Still catastrophic consequences", used current climate models to look at the consequences of a global nuclear war involving most or all of the world's current nuclear arsenals (which the authors judged to be one the size of the world's arsenals twenty years earlier). The authors used a global circulation model, ModelE from the NASA Goddard Institute for Space Studies, which they noted "has been tested extensively in global warming experiments and to examine the effects of volcanic eruptions on climate." The model was used to investigate the effects of a war involving the entire current global nuclear arsenal, projected to release about 150 Tg of smoke into the atmosphere, as well as a war involving about one third of the current nuclear arsenal, projected to release about 50 Tg of smoke. In the 150 Tg case they found that:
A global average surface cooling of –7 °C to –8 °C persists for years, and after a decade the cooling is still –4 °C (Fig. 2). Considering that the global average cooling at the depth of the last ice age 18,000 yr ago was about –5 °C, this would be a climate change unprecedented in speed and amplitude in the history of the human race. The temperature changes are largest over land ... Cooling of more than –20 °C occurs over large areas of North America and of more than –30 °C over much of Eurasia, including all agricultural regions.
In addition, they found that this cooling caused a weakening of the global hydrological cycle, reducing global precipitation by about 45%. As for the 50 Tg case involving one third of current nuclear arsenals, they said that the simulation "produced climate responses very similar to those for the 150 Tg case, but with about half the amplitude," but that "the time scale of response is about the same." They did not discuss the implications for agriculture in depth, but noted that a 1986 study which assumed no food production for a year projected that "most of the people on the planet would run out of food and starve to death by then" and commented that their own results show that "this period of no food production needs to be extended by many years, making the impacts of nuclear winter even worse than previously thought."
Following Iraq's invasion of Kuwait and Iraqi threats of igniting the country's 800 or so oil wells were made, speculation on the cumulative climatic effect of this, presented at the World Climate Conference in Geneva that November in 1990, ranged from a nuclear winter type scenario, to heavy acid rain and even short term immediate global warming. As threatened, the wells were set ablaze by the retreating Iraqis by March 1991 and the 600 or so successfully set Kuwaiti oil wells were not fully extinguished until November 6, 1991, eight months after the end of the war, and they consumed an estimated six million barrels of oil daily at their peak intensity.
In articles printed in the Wilmington morning star and the Baltimore Sun newspapers of January 1991, prominent authors of nuclear winter papers - Richard P. Turco, John W. Birks, Carl Sagan, Alan Robock and Paul Crutzen together collectively stated that they expected catastrophic nuclear winter like effects with continental sized impacts of "sub-freezing" temperatures as a result of if the Iraqis went through with their threats of igniting 300 to 500 pressurized oil wells and they burned for a few months.
Later when Operation Desert Storm had begun in late January 1991, coinciding with the first few oil fires being lit, Dr. S. Fred Singer and Carl Sagan discussed the possible environmental impacts of the Kuwaiti petroleum fires on the ABC News program Nightline. Sagan again argued that some of the effects of the smoke could be similar to the effects of a nuclear winter, with smoke lofting into the stratosphere, a region of the atmosphere beginning around 48,000 feet (15,000 m) above sea level at Kuwait, resulting in global effects and that he believed the net effects would be very similar to the explosion of the Indonesian volcano Tambora in 1815, which resulted in the year 1816 being known as the Year Without a Summer.
He reported on initial modeling estimates that forecast impacts extending to south Asia, and perhaps to the northern hemisphere as well. Sagan stressed this outcome was so likely that "it should affect the war plans." Singer, on the other hand, said that his calculations showed that the smoke would go to an altitude of about 3,000 feet (910 m) and then be rained out after about three to five days and thus the lifetime of the smoke would be limited. Both height estimates made by Singer and Sagan turned out to be wrong, albeit with Singers narrative being closer to what transpired, with the comparatively minimal atmospheric effects remaining limited to the Persian Gulf region, with smoke plumes, in general, lofting to about 10,000 feet (3,000 m) and a few times as high as 20,000 feet (6,100 m).
Sagan later conceded in his book The Demon-Haunted World that his predictions obviously did not turn out to be correct: "it was pitch black at noon and temperatures dropped 4–6 °C over the Persian Gulf, but not much smoke reached stratospheric altitudes and Asia was spared."
Sagan and his colleagues expected that a "self-lofting" of the sooty smoke would occur when it absorbed the sun's heat radiation, with little to no scavenging occurring, whereby the black particles of soot would be heated by the sun and lifted/lofted higher and higher into the air, thereby injecting the soot into the stratosphere, a position where they argued it would take years for the sun blocking effect of this aerosol of soot to fall out of the air, and with that, catastrophic ground level cooling and agricultural impacts in Asia and possibly the Northern Hemisphere as a whole.
The Atmospheric scientist tasked with studying the atmospheric impact of the Kuwaiti fires by the National Science Foundation, Peter Hobbs, stated that "the fires' modest impact suggested that "some numbers [used to support the Nuclear Winter hypothesis]... were probably a little overblown."
Hobb's found that at the peak of the fires, the smoke absorbed 75 to 80% of the sun’s radiation. The particles rose to a maximum of 20,000 feet (6,100 m), and when combined with scavenging by clouds the smoke had a short residency time of a maximum of a few days in the atmosphere.
Pre-war claims of wide scale, long-lasting, and significant global environmental impacts were thus not borne out and found to be significantly exaggerated by the media and speculators, with climate models by those not supporting the nuclear winter hypothesis at the time of the fires predicting only more localized effects such as a daytime temperature drop of ~10 °C within ~200 km of the source.
Oil well and oil reserve smoke pluming to the stratosphere and serving as a main contributor to the soot of a nuclear winter was a central tenet of the early climatology papers on the hypothesis, they were considered to possibly be more of a contributor than cities as the smoke from oil has a higher propensity for being black, thus absorbing more sunlight. Following the results of the Kuwaiti oil fires being in disagreement with the core nuclear winter promoting scientists, the 1990s+ nuclear winter papers generally attempt to distance themselves from suggesting oil well and reserve smoke will reach the stratosphere.
The 2007 study discussed above noted that modern computer models have been applied to the Kuwait oil fires, finding that individual smoke plumes are not able to loft smoke into the stratosphere, but that smoke from fires covering a large area[quantify] like some forest fires can lift smoke[quantify] into the stratosphere, and this is supported by recent evidence that it occurs far more often than previously thought. The study also suggested that the burning of the comparably smaller cities, which would be expected to follow a nuclear strike, would also loft significant amounts of smoke into the stratosphere:
Stenchikov et al. [2006b] conducted detailed, high-resolution smoke plume simulations with the RAMS regional climate model [e.g., Miguez-Macho et al., 2005] and showed that individual plumes, such as those from the Kuwait oil fires in 1991, would not be expected to loft into the upper atmosphere or stratosphere, because they become diluted. However, much larger plumes, such as would be generated by city fires, produce large, undiluted mass motion that results in smoke lofting. New large eddy simulation model results at much higher resolution also give similar lofting to our results, and no small scale response that would inhibit the lofting [Jensen, 2006].
The eruption of the Philippines volcano Mount Pinatubo ejected roughly 10 km3 (2.4 cu mi) of magma and 17,000,000 tonnes (19,000,000 short tons) of SO2, mostly during the explosive Plinian/Ultra-Plinian event of June 15, 1991, creating a global stratospheric SO2 haze layer which persisted for six months. Despite introducing ten times as much SO2 as the Kuwaiti fires, global temperatures dropped by only about 0.5 °C (0.9 °F), and despite a several-month 10% drop in solar irradiation, there was no global impact to agriculture.
In June 1957, The Effects of Nuclear Weapons by Samuel Glasstone was published containing a section entitled "Nuclear Bombs and the Weather" (pages 69–71), which states: "The dust raised in severe volcanic eruptions, such as that at Krakatoa in 1883, is known to cause a noticeable reduction in the sunlight reaching the earth ... The amount of debris remaining in the atmosphere after the explosion of even the largest nuclear weapons is probably not more than about 1 percent or so of that raised by the Krakatoa eruption. Further, solar radiation records reveal that none of the nuclear explosions to date has resulted in any detectable change in the direct sunlight recorded on the ground."
In 1974, John Hampson suggested that a full-scale nuclear exchange could result in depletion of the ozone shield, possibly subjecting the earth to ultraviolet radiation for a year or more. In 1975, the United States National Research Council (NRC) reported on ozone depletion following nuclear war, judging that the effect of dust would probably be slight climatic cooling.
In 1981, William J. Moran began discussions and research in the NRC on the dust effects of a large exchange of nuclear warheads. An NRC study panel on the topic met in December 1981 and April 1982.
As part of a study launched in 1980 by Ambio, a journal of the Royal Swedish Academy of Sciences, Paul Crutzen and John Birks circulated a draft paper in early 1982 with the first quantitative evidence of alterations in short-term climate after a nuclear war. In 1982, a special issue of Ambio devoted to the possible environmental consequences of nuclear war included a paper by Crutzen and Birks anticipating the nuclear winter scenario. The paper discussed particulates from large fires, nitrogen oxide, ozone depletion and the effect of nuclear twilight on agriculture. Crutzen and Birks showed that smoke injected into the atmosphere by fires in cities, forests and petroleum reserves could prevent up to 99% of sunlight from reaching the Earth's surface, with major climatic consequences: "The normal dynamic and temperature structure of the atmosphere would therefore change considerably over a large fraction of the Northern Hemisphere, which will probably lead to important changes in land surface temperatures and wind systems." An important implication of their work was that a "first strike" nuclear attack would have severe consequences for the perpetrator.
Interest in nuclear war environmental effects also arose in the USSR. After becoming aware of the papers by N.P.Bochkov and E.I.Chazov, Russian atmospheric scientist Georgy Golitsyn applied his research on dust-storms to the situation following a large nuclear war. His suggestion that the atmosphere would be heated and that the surface of the planet would cool appeared in The Herald of the Academy of Sciences in September 1983.
In 1982, the so-called TTAPS team (Richard P. Turco, Owen Toon, Thomas P. Ackerman, James B. Pollack and Carl Sagan) undertook a computational modeling study of the atmospheric consequences of nuclear war, publishing their results in Science in December 1983. The phrase "nuclear winter" was coined by Turco just prior to publication. In this early work, TTAPS carried out the first estimates of the total smoke and dust emissions that would result from a major nuclear exchange, and determined quantitatively the subsequent effects on the atmospheric radiation balance and temperature structure. To compute dust and smoke impacts, they employed a one-dimensional microphysics/radiative-transfer model of the Earth's lower atmosphere (to the mesopause), which defined only the vertical characteristics of the global climate perturbation.
Upon learning of the TTAPS scenarios, Vladimir Alexandrov and G. I. Stenchikov also published a report in 1983 on the climatic consequences of nuclear war based on simulations with a three-dimensional global circulation model. Two years later Vladimir Alexandrov disappeared under mysterious circumstances. Richard Turco and Starley L. Thompson were critical of the Soviet model, Turco claimed it was "a primitive rendition of an obsolete US model".
In 1984 the WMO commissioned Georgy Golitsyn and N. A. Phillips to review the state of the science. They found that studies generally assumed a scenario that half of the world's nuclear weapons would be used, ~5000 Mt, destroying approximately 1,000 cities, and creating large quantities of carbonaceous smoke - 1–2×1014 g being mostly likely, with a range of 0.2–6.4×1014 g (NAS; TTAPS assumed 2.25×1014). The smoke resulting would be largely opaque to solar radiation but transparent to infra-red, thus cooling by blocking sunlight but not causing warming from enhancing the greenhouse effect. The optical depth of the smoke can be much greater than unity. Forest fires resulting from non-urban targets could increase aerosol production further. Dust from near-surface explosions against hardened targets also contributes; each Mt-equivalent of explosion could release up to 5 million tons of dust, but most would quickly fall out; high altitude dust is estimated at 0.1-1 million tons per Mt-equivalent of explosion. Burning of crude oil could also contribute substantially.
The 1-D radiative-convective models used in these studies produced a range of results, with coolings up to 15–42 °C between 14 and 35 days after the war, with a "baseline" of about 20 °C. Somewhat more sophisticated calculations using 3-D GCMs (Alexandrov and Stenchikov (1983); Covey, Schneider and Thompson (1984); produced similar results: temperature drops of between 20 and 40 °C, though with regional variations.
All calculations show large heating (up to 80 °C) at the top of the smoke layer at about 10 km; this implies a substantial modification of the circulation there and the possibility of advection of the cloud into low latitudes and the southern hemisphere.
The report made no attempt to compare the likely human impacts of the post-war cooling to the direct deaths from explosions.
In 1987 P. M. Kelly of the University of East Anglia Climatic Research Unit stated that "although there are a handful of vociferous critics, the atmospheric community is united in its conclusion that the threat of nuclear winter is genuine".
In 1990, in a paper entitled "Climate and Smoke: An Appraisal of Nuclear Winter," TTAPS give a more detailed description of the short- and long-term atmospheric effects of a nuclear war using a three-dimensional model:
First 1 to 3 months:
Following 1 to 3 years:
The Soviet origins of the hypothesis, albeit not any of Tretyakov's other claims, is supported by Dr. Vitalii Nikolaevich Tsygichko, a Senior Analyst at the Soviet Academy of Sciences, the author of the study, Mathematical Model of Soviet Strategic Operations on the Continental Theater, and a former member of the General Staff, as he stated that Soviet military analysts discussed the idea of a "nuclear winter" (although they did not use that exact term) years before U.S. scientists wrote about it in the 1980s.
Conversely, Starley L. Thompson of the National Center for Atmospheric Research, Boulder, Colorado, claimed that the Soviet Union's 1980s nuclear winter models were developed in the United States in the early 1970s.
In 2014, M. J. Mills (at the US National Center for Atmospheric Research, NCAR), O. B. Toon (of the original TTAPS team), J. Lee-Taylor, and A. Robock published "Multi-decadal global cooling and unprecedented ozone loss following a regional nuclear conflict" in the journal Earth's Future. The authors used computational models developed by NCAR to simulate the climatic effects of a regional nuclear war in which 100 "small" (15 kt) weapons are detonated over cities. They concluded, in part, that
global ozone losses of 20-50% over populated areas, levels unprecedented in human history, would accompany the coldest average surface temperatures in the last 1000 years. We calculate summer enhancements in UV indices of 30-80% over Mid-Latitudes, suggesting widespread damage to human health, agriculture, and terrestrial and aquatic ecosystems. Killing frosts would reduce growing seasons by 10-40 days per year for 5 years. Surface temperatures would be reduced for more than 25 years, due to thermal inertia and albedo effects in the ocean and expanded sea ice. The combined cooling and enhanced UV would put significant pressures on global food supplies and could trigger a global nuclear famine.
The TTAPS study was widely reported and criticized in the media. Later model runs in some cases predicted less severe effects, but continued to support the overall conclusion of significant global cooling. Recent studies (2006) substantiate that smoke from urban firestorms in a local nuclear war would lead to long lasting global cooling but in a less dramatic manner than a global nuclear war, while a 2007 study of the effects of global nuclear war supported the conclusion that it would lead to full-scale nuclear winter.
The original work by Sagan and others was criticized as a "myth" and "discredited theory" in the 1987 book Nuclear War Survival Skills, a civil defense manual by Cresson Kearny for the Oak Ridge National Laboratory. Kearny said the maximum estimated temperature drop would be only about by 20 degrees Fahrenheit (11 degrees Celsius), and that this amount of cooling would last only a few days. He also suggested that a global nuclear war would indeed result in millions of deaths from hunger, but primarily due to cessation of international food supplies, rather than due to climate changes.
Kearny, who was not a climate scientist himself, based his conclusions almost entirely on the 1986 paper "Nuclear Winter Reappraised" by Starley Thompson and Stephen Schneider. However, a 1988 article by Brian Martin in Science and Public Policy states that although their paper concluded the effects would be less severe than originally thought, with the authors describing these effects as a "nuclear autumn", other statements by Thompson and Schneider show that they "resisted the interpretation that this means a rejection of the basic points made about nuclear winter". In addition, the authors of the 2007 study above state that "because of the use of the term 'nuclear autumn' by Thompson and Schneider , even though the authors made clear that the climatic consequences would be large, in policy circles the theory of nuclear winter is considered by some to have been exaggerated and disproved [e.g., Martin, 1988]." And in 2007 Schneider emphasized the danger of serious climate changes from a limited nuclear war of the kind analyzed in the 2006 study above, saying "The sun is much stronger in the tropics than it is in mid-latitudes. Therefore, a much more limited war [there] could have a much larger effect, because you are putting the smoke in the worst possible place."
John Maddox, editor of the journal Nature, issued a series of skeptical comments about nuclear winter studies during his tenure, being a long-time critic of environmental doomsdayism. Similarly S. Fred Singer was a long term vocal critic of the hypothesis in the journal and in televised debates with Carl Sagan. Russell Seitz, Associate of the Harvard University Center for International Affairs, argues that the models assumptions give results which the researchers want to achieve and is a case of "worst-case analysis run amok".
In 1986, atmospheric scientist Joyce Penner from the Lawrence Livermore National Laboratory published an article in Nature in which she focused on the specific variables of the smokes optical properties and the quantity of smoke remaining airborne after the city fires and found that the published estimates of these variables varied so widely that depending on which estimates were chosen the climate effect would be minor/negligible or massive.
During the early 1980s, Fidel Castro recommended to the Kremlin a harder line against Washington, even suggesting the possibility of nuclear strikes. The pressure stopped after Soviet officials gave Castro a briefing on the ecological impact on Cuba of nuclear strikes on the United States. In 2010 Alan Robock, a co-author of nuclear winter papers was summoned to Cuba to help Castro promote his new view that nuclear war would bring about Armageddon, Robock's 90 minute lecture was later aired on nationwide television in the country. However according to Robock, in so far as getting US government attention and affecting nuclear policy, he has failed. In 2009, together with Owen Toon, he gave a talk to the United States Congress but nothing transpired from it and the then presidential science adviser, John Holdren, did not respond to their requests in 2009 or at the time of writing in 2011.
In an interview in 2000, Mikhail Gorbachev, in response to the comment "In the 1980s, you warned about the unprecedented dangers of nuclear weapons and took very daring steps to reverse the arms race," said "Models made by Russian and American scientists showed that a nuclear war would result in a nuclear winter that would be extremely destructive to all life on Earth; the knowledge of that was a great stimulus to us, to people of honor and morality, to act in that situation."
However a 1984 US Interagency Intelligence Assessment express's a far more skeptical and cautious approach by stating that as the hypothesis is not convincing scientifically, they predicted that Soviet nuclear policy would be to maintain their strategic nuclear posture, such as their fielding of the high throw-weight SS-18 missile and they would merely attempt to exploit the hypothesis for propaganda purposes, such as directing scrutiny on the US portion of the nuclear arms race. Moreover it goes on to express the belief that if nuclear winter did begin to be taken seriously by Soviet officials it would probably cause them to demand exceptionally high standards of scientific proof for the hypothesis as the implications of it would undermine their military doctrine, a level of scientific proof which perhaps could not be met without field experimentation. The un-redacted portion of the document ends with the suggestion that substantial increases in Soviet Civil defense food stockpiles might be an early indicator that Nuclear Winter was beginning to influence Soviet upper echelon thinking.
As the implications of nuclear winter began to be taken seriously in the late 1980s, military analysts turned to reinforce existing trends toward development of lower yield and better accuracy nuclear warheads, that would explode at low altitudes and cause less thermal radiation ignited fires, thus reducing the likelihood of a nuclear winter. While the TTAPS paper had described a 3000 Mt counterforce attack on ICBM sites; Michael Altfeld of Michigan State University and political scientist Stephen Cimbala of Pennsylvania State University argued that smaller, more accurate warheads and lower detonation heights could produce the same counterforce strike with only 3 Mt and produce less climatic effects, even if cities were targeted, as lower fuzing heights, such as surface bursts, would limit the range of the burning thermal rays due to terrain masking and shadows cast by buildings, while also temporarily lofting far more radioactive soil into the atmosphere. This logic is similarly reflected in the 1984 Interagency Intelligence assessment, which suggests that targeting planners would simply have to consider target combustibility along with yield, height of burst, timing and other factors to reduce the amount of smoke to safeguard against the potentiality of a nuclear winter. Therefore as a consequence of attempting to limit the target fire hazard by reducing the range of thermal radiation with fuzing for surface bursts, this will result in a scenario where the far more concentrated, and therefore deadlier, local fallout that is generated following a surface burst forms, as opposed to the comparatively dilute global fallout created when nuclear weapons are fuzed in air burst mode.
Altfeld and Cimbala also suggested that belief in the possibility of nuclear winter has actually made nuclear war more likely, contrary to the views of Sagan and others, because it has inspired the development of more accurate, and lower explosive yield, nuclear weapons. By replacing all the then Cold War viewed strategic nuclear weapons in the multi-megaton yield range, with weapons with yields closer to tactical nuclear weapons.