Nuclear winter

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Nuclear winter (also known as atomic winter) is a hypothesized^[1][2] global climatic effect most often considered a potential threat following a countervalue (or city-targeted) nuclear war as a result of city and natural wildfire firestorms.^[3] It is most frequently suggested to manifest as a result of the combined combustion pollution from the burning of at least 100 city sized areas at firestorm-intensity. The term was specifically coined to refer to computer model results where this smoke remained in the air for years, or even decades, and during this time it causes massive planet-wide temperature drops ("winters").

The climate models in the public domain suggest that the ignition of 100 firestorms, comparable in intensity to that observed in Hiroshima in 1945, would produce a "small" nuclear winter.^[4][5] The burning of these firestorms would result in the injection of soot (specifically black carbon) into the Earth's stratosphere, producing an anti-greenhouse effect that lowers the Earth's surface temperature. Alan Robock's model suggests that the cumulative products of 100 of these firestorms would unmistakably cool the global climate by approximately 1 °C (1.8 °F), largely eliminating the magnitude of anthropogenic global warming for two to three years. Robock has not modeled, but speculated, that this would have global agricultural losses as a consequence.^[6]

A much larger number of firestorms, however, was the initial assumption of the computer modelers that coined the term in the 1980s. These were speculated to be a result of any large scale employment of countervalue city-airbursting nuclear weapon use during an American-Soviet total war. This larger number of firestorms, which are not, in themselves, modeled,^[7] are presented as causing nuclear winter conditions as a result of the smoke inputted into various climate models, with the depths of severe cooling lasting for as long as a decade, summer drops in average temperature by about 20 °C (36 °F) in core agricultural regions of the US, Europe, and China, and by as much as 35 °C (63 °F) in Russia.^[8] This cooling was produced due to a 99% reduction in the natural solar radiation reaching the surface of the planet in the first few years, gradually clearing over several decades.^[9]

As nuclear devices need not be involved in the ignition of a firestorm, the term is a common misnomer.^[10] This is due to, in greatest part, the vast majority of published papers stating, without qualitative justification, that nuclear explosions are the cause of the modeled firestorm effects. The only phenomenon that is scrutinized and computer modeled in the nuclear winter papers is the climate forcing agent of firestorm-soot, a product which can be ignited and formed by a myriad of other, more common, means.^[10] Although rarely discussed, the proponents of the hypothesis do state that the same "nuclear winter" effect would occur if 100 conventionally lit firestorms were ignited.^[11]

On the fundamental level, since the advent of photographic evidence of tall clouds were captured,^[12] it was known that firestorms can inject soot smoke/aerosols into the stratosphere, more recently however it has been found that each natural occurrence of a wildfire firestorm can "surprisingly frequently" produce minor "nuclear winter" effects, with short-lived, almost immeasurable drops in surface temperatures, confined to the global hemisphere that they burned in.^{[3][13][14][15]} This is somewhat analogous to the frequent volcanic eruptions that inject sulfates into the stratosphere and thereby produce minor, even negligible, volcanic winter effects.

A suite of satellite and aircraft-based firestorm-soot-monitoring instruments are at the forefront of attempts to accurately determine the lifespan, quantity, injection height, and optical properties of this smoke.^{[16][17][18][19][20]} Information regarding all of these properties is necessary to truly ascertain the length and depth of the cooling effect of firestorms, independent of the nuclear winter computer model projections.

Presently, from satellite tracking data, stratospheric smoke aerosols are removed in a time span under approximately two months.^[18] The existence of any hint of a tipping point into a new stratospheric condition where the aerosols would not be removed within this time frame remains to be determined.^[18]

Mechanism

Picture of a pyrocumulonimbus cloud taken from a commercial airliner cruising at about 10 km. In 2002 various sensing instruments detected 17 distinct pyrocumulonimbus cloud events in North America alone.^[13]

The nuclear winter scenario assumes that 100 or more city firestorms^[21][22] are ignited by the nuclear explosions of a nuclear war,^[23] and the firestorms lift 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 soot in 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 heat the stratosphere and block out a portion of the sun's light from reaching the surface, 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 months to years on end.

The modeled stable inversion layer of hot soot between the troposphere and high stratosphere that produces the anti-greenhouse effect was dubbed the "Smokeosphere" by Stephen Schneider et al. in their 1988 paper.^[24][25][26]

Although it is common in the climate models for the city firestorms to be ignited by nuclear explosions, they need not be ignited by nuclear devices;^[10] more conventional ignition sources can instead be the spark of the firestorms. As prior to the previously mentioned solar heating effect, the soot's injection height is controlled by the rate of energy release from the firestorm's fuel, not the size, or lack thereof, of an initial nuclear explosion.^[22] For example, the mushroom cloud from the bomb dropped on Hiroshima reached a height of six kilometers (middle troposphere) within a few minutes and then dissipated due to winds, while the individual fires within the city took almost three hours to form into a firestorm and produce a "pyrocumulus" cloud, a cloud that is assumed to have reached upper tropospheric heights, as over its multiple hours of burning, the firestorm released an estimated 1000 times the energy of the bomb.^[27]

As the incendiary effects of a nuclear explosion do not present any especially characteristic features.^[28] It is estimated by those with Strategic bombing experience, that as the city was a firestorm hazard, the same fire ferocity and building damage produced at Hiroshima by one 16-kiloton nuclear bomb from a single B-29 bomber could have been produced instead by the conventional use of about 1,200 tons/1.2 kilotons of incendiary bombs from 220 B-29s distributed over the city.^[28][29][30]

While the firestorm of Dresden and Hiroshima and the mass fires of Tokyo and Nagasaki occurred with mere months separating them in 1945, the more intense and conventionally lit Hamburg firestorm occurred in 1943. Despite the separation in time, ferocity and area burned leading modelers of the hypothesis state that these five fires potentially placed five percent as much smoke into the stratosphere as the hypothetical 100 nuclear-ignited fires of modern models.^[11] While it is believed that the modeled climate-cooling-effects from the mass of soot assumed to be injected into the stratosphere by 100 firestorms (one to five teragrams) would have been detectable with technical instruments in WWII, only five percent of that would not have been possible to observe at that time.^[11]

Aerosol removal timescale

Smoke rising in Lochcarron, Scotland, is stopped by an overlying natural low-level inversion layer of warmer air (2006).

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.^[31]

The most important physical removal mechanism is "rainout", both during the "fire-driven convective column" phase—which produces "black rain" near the fire site—and rainout after the convective plume's dispersal, where the smoke is no longer concentrated and thus "wet removal" is believed to be "very efficient."^[32] However these efficient removal mechanisms in the troposphere are avoided in the Robock 2007 study, where solar heating is modeled to quickly "loft" the soot into the stratosphere, "detraining" or separating the darker soot particles from the fire clouds' whiter water condensation.^[33]

Once in the stratosphere, the physical removal mechanisms affecting the timescale of the soot particles' residence are how quickly the aerosol of soot collides and coagulates with other particles via Brownian motion,^[34][35][36] and falls out of the atmosphere via gravity-driven dry deposition,^[36] and the time it takes for the "phoretic effect" to move coagulated particles to a lower level in the atmosphere.^[31] Whether by coagulation or the phoretic effect, 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 carbonaceous component of the smoke, via reactions with oxidative species such as ozone and nitrogen oxides, both of which are found at all levels of the atmosphere,^[37][38] and which also occur at greater concentrations when air is heated to high temperatures, which will be discussed later.

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 one-to-two-year time scale.^[39]

The satellite tracking of wildfire smoke aerosols from the 17 North American pyrocumulonimbus-cloud-injection events in 2002, indicates that the aerosols are removed in a time span under approximately two months,^[18] although the exact mechanisms by which they are removed, and the existence of any hint of a tipping point into a new stratospheric condition were the aerosols would not be removed within this timeframe, remains to be experimentally determined.^[18]

Aerosol–atmosphere interactions are still poorly understood.^[40][41]

Soot properties

Sooty aerosols can have a wide range of properties, as well as complex shapes, making it difficult to determine their evolving atmospheric Optical depth value. The conditions present during the creation of the soot are believed to be considerably important as to their final properties, with soot generated on the more efficient spectrum of burning efficiency considered almost "elemental carbon black," while on the more inefficient end of the burning spectrum, greater quantities of partially burnt/oxidized fuel are present. These partially burnt "organics" as they are known, often form "tar balls" and "brown carbon" during common lower-intensity wildfires, and can also coat the purer carbon black particles.^[42][43][44] However, as the soot of greatest importance is that which is injected to the highest altitudes by the pyroconvection of the firestorm—a fire being fed with storm-force winds of air—it is estimated that the majority of the soot under these conditions is of the more oxidized carbon black nature.^[45]

Consequences

Diagram obtained by the CIA from the international seminar on nuclear war in Italy 1984. It depicts the findings of Soviet 3-D computer model research on nuclear winter from 1983, and although containing similar errors as earlier Western models, it was the first 3-D model of nuclear winter. (The three dimensions in the model are longitude, latitude and altitude.)^[46] The diagram shows the models predictions of global temperature changes after a global nuclear exchange. Top shows effects after 40 days, bottom after 243 days. A co-author was nuclear winter modelling pioneer Vladimir Alexandrov.^[47][48]

Climatic effects

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".^[49][50]

Ozone depletion

A 2008 study by Michael J. Mills and coauthors, published in the Proceedings of the National Academy of Sciences, 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.^[51] 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 surface chemistry reactions that would break down the stratospheric ozone layer protecting Earth from harmful ultraviolet radiation.

Nuclear summer

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 the decay of the organic matter that froze during the nuclear winter.^[52][53] It is supported scientifically far less, than nuclear winter, as a risk.

History

Early work

The mushroom cloud height as a function of explosive yield detonated as surface bursts.^[54][55] As charted, yields at least in the megaton range are required to lift dust/fallout into the stratosphere. Ozone reaches its maximum concentration at about 25 km (c. 82,000 ft) in altitude.^[54] Another means of stratospheric entry is from high altitude nuclear detonations, one example of which includes the 10.5 kiloton Soviet test no. #88 of 1961, detonated at 22.7 km.^[56][57] US high-yield upper atmospheric tests, Teak and Orange were also assessed for their ozone destruction potential.^[58][59]
0 = Approx altitude commercial aircraft operate
1 = Fat Man
2 = Castle Bravo

In 1952, a few weeks prior to the Ivy Mike (10.4 megaton) test on Elugelab island, there was a concern that the "small particles"/aerosols lifted by the explosion might cool the Earth. Major Norair Lulejian, USAF, and astronomer Natarajan Visvanathan, studied this possibility reporting their findings in Effects of Superweapons Upon the Climate of the World. According to a document by the Defense Threat Reduction Agency, this report was the initial study of the "nuclear winter" concept that was popularized by others decades later. It indicated no appreciable chance of explosion-induced climate change.^[60]

Following numerous surface bursts of high yield "Hydrogen bomb" explosions on Pacific Proving Ground islands such as those of Ivy Mike in the year 1952 and Castle Bravo (15 megaton) in 1954, The Effects of Nuclear Weapons by Samuel Glasstone was published in 1957 which contained 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 [soil or other surface] 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."^[61] The US Weather Bureau in 1956 regarded it as conceivable that a large enough nuclear war with megaton-range surface detonations, could lift enough soil to cause a new ice age.^[62]

In the 1966 RAND corporation memorandum The Effects of Nuclear War on the Weather and Climate by E. S. Batten, while primarily analysing potential dust effects from surface bursts,^[63] it notes "in addition to the effects of the debris, extensive fires ignited by nuclear detonations might change the surface characteristics of the area and modify local weather patterns...however, a more thorough knowledge of the atmosphere is necessary to determine their exact nature, extent, and magnitude."^[64]

In the 1985 The Effects on the Atmosphere of a Major Nuclear Exchange, it argues that a "plausible" estimate on the amount of stratospheric dust injected following a surface burst of 1 megaton is 0.3 teragrams, of which "8 percent" would be in the submicron/micrometer range.^[65] The potential cooling from soil dust was again looked at in 1992, in a US National Academy of Sciences (NAS)^[66] report on geoengineering, which estimated that about 10¹⁰ kg [100 teragrams] of stratospheric injected soil dust with particulate grain dimensions of 0.1 to 1 micrometer would be required to mitigate the warming from a doubling of atmospheric CO₂, that is, to produce ~ 2 degree celsius of cooling.^[67]

In 1969, Paul Crutzen discovered that NOx (oxides of nitrogen) could be an efficient catalyst for the destruction of the ozone layer/stratospheric ozone.^[68] With studies on the potential effects of NOx generated by engine heat in stratosphere flying Supersonic Transport (SST) airplanes in the 1970s serving as a backdrop,^[69][70] John Hampson in 1974 suggested in the journal Nature that due to the nuclear fireballs creation of atmospheric NOx, 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.^[71][72] Hampson's hypothesis "led directly",^[73] in 1975, to the United States National Research Council (NRC) reporting on the models of ozone depletion following nuclear war in the book Long-Term Worldwide Effects of Multiple Nuclear-Weapons Detonations.^[71] In this 1975 book it states that a nuclear war involving 4000Mt (megaton) from present arsenals would probably deposit much less dust in the stratosphere than the Krakatoa eruption, judging that the effect of dust and oxides of nitrogen would probably be slight climatic cooling which "would probably lie within normal global climatic variability, but the possibility of climatic changes of a more dramatic nature cannot be ruled out".^[69][71][74] While on the issue of fireball generated NOx and ozone layer loss therefrom, its model calculations in the early-to-mid 1970s on the effects of a nuclear war with the use of large numbers of multi-megaton yield detonations returned conclusions that this could reduce ozone levels by 50 per cent or more in the northern hemisphere.^[75][76]

However from the historical data, a far more authoritative source, a paper in 1973 as it appeared in the journal Nature depicts both the stratospheric ozone levels worldwide overlayed upon the number of nuclear detonations during the era of atmospheric testing, the authors conclude that neither the data nor their models show any correlation between the 500 or so megatons in historical atmospheric testing and when ozone increased or decreased in concentration.^[77] In 1976 a study on the experimental measurements of an earlier atmospheric nuclear test as it affected the ozone layer, also found that nuclear detonations are tentatively exonerated in depleting ozone, after the at first, alarming model calculations of the time.^[78] Similarly a 1981 paper found that models on ozone destruction from one test, and physical measurements taken, were in disagreement, as no destruction was observed.^[79] In total about 500 megatons were atmospherically detonated between 1945 and 1971,^[80] with a peak occurring in 1961–62, when 340 megatons were detonated in the atmosphere by the United States and Soviet Union.^[81] During this 1–2 year peak, counting only the multi-megaton range detonations in the two nations nuclear test series, a total yield estimated at 300 megatons of energy was released, due to this, 3 × 10³⁴ additional molecules of nitric oxide (about 5000 tons per megaton, "5 x 10^9 g per Mton"^[77][82]) are believed to have entered the stratosphere, and while ozone depletion of 2.2 percent was noted in 1963, the decline had started prior to 1961 and is believed to have been caused by other meteorological effects, thus the 1985 book The Effects on the Atmosphere of a Major Nuclear Exchange states: "one can not draw definite conclusions about the effects of nuclear explosions on stratospheric ozone".^[77][83]

In 1982 Australian physicist Brian Martin, who frequently corresponded with John Hampson,^[84] penned a short historical synopsis on the history of interest in the effects of the direct NOx generated by nuclear fireballs, and in doing so, also outlined Hampson's other non-mainstream viewpoints, particularly those relating to greater ozone destruction from upper-atmospheric detonations as a result of any widely used anti-ballistic missile (ABM-1 Galosh) system.^[85] However, Martin ultimately concludes that it is "unlikely that in the context of a major nuclear war" ozone degradation would be of serious concern. Singling out views about potential ozone loss and therefore increases in Ultraviolet light leading to the widespread destruction of crops, as advocated by journalist Jonathan Schell in his popular 1982 book The Fate of the Earth, as highly unlikely.^[76]

More recent accounts on the specific ozone layer destruction potential of NOx species, are much less than earlier assumed from simplistic calculations, as "about 1.2 million tons" of natural and anthropogenic generated stratospheric NOx is believed to be formed each year according to Robert P.Parson in the 1990s.^[68]

Science Fiction

The first published suggestion that a cooling of climate or winter could be an effect of a nuclear war, appears to have been originally put forth by Poul Anderson and F.N Waldrop in their post war story "Tomorrow's Children", which was contained in the March 1947 issue of the Astounding Science Fiction magazine, the story which is primarily about a team of scientists hunting down mutants,^[86] warns of a "Fimbulwinter" caused by dust that blocked sunlight after the recent fictitious nuclear war and speculates that this may even trigger a new ice age.^[87][88] Anderson went on to publish a novel based partly on this story in 1961 titling it; Twilight World.^[89] Similarly in 1985 it was noted by T.G Parsons that the story Torch by C. Anvil, which likewise appeared in Astounding Science Fiction magazine but in the April 1957 edition, contains the essence of the "Twilight at Noon"/"nuclear winter" hypothesis. In the story a nuclear warhead ignites an oil field and the soot produced "screens out part of the sun's radiation" which results in Arctic temperatures for much of the population of North America and the Soviet Union.^[90]

1980s

The 1988 Air Force Geophysics Laboratory publication An assessment of global atmospheric effects of a major nuclear war by Muench, H. Stuart et al. contains a chronology and review of the major reports on the nuclear winter hypothesis from 1983-86. In general these reports arrive at similar conclusions as they are based on the same "assumptions, the same basic data" with minor model-code differences "to arrive at the same answer". They skip the modeling steps of assessing the possibility of fire and the initial fire plumes and instead start the modeling process with a "spatially uniform" "soot cloud" which has found its way into the atmosphere.^[91]

Although never openly acknowledged by the multi-disciplinary team who authored the most popular 1980s TTAPS model, in 2011 the American Institute of Physics states that the TTAPS team's announcement of their results in 1983, "was with the explicit aim of promoting international arms control".^[92] Yet "the computer models were so simplified, and the data on smoke and other aerosols were still so poor, that the scientists could say nothing for certain."^[93]

In 1981, William J. Moran began discussions and research in the National Research Council(NRC) on the airborne soil/dust effects of a large exchange of nuclear warheads, having seen a possible parallel in the dust effects of a war with that of the asteroid created K-T boundary and its popular analysis a year earlier by Luis Alvarez in 1980.^[94] An NRC study panel on the topic met in December 1981 and April 1982 in preparation for the release of the NRC's The Effects on the Atmosphere of a Major Nuclear Exchange, published in 1985.^[71]

As part of a study on the creation of oxidizing species such as NOx and ozone in the troposphere after a nuclear war,^[95] launched in 1980 by AMBIO, a journal of the Royal Swedish Academy of Sciences, Paul J. Crutzen and John Birks began preparing for the 1982 publication of a calculation on the effects of nuclear war on stratospheric ozone, using the latest models for the time. However they found that in part as a result of the trend towards more numerous but less energetic, sub-megaton range nuclear warheads (made possible by the ceaseless march to increase ICBM warhead accuracy/Circular Error Probable) the ozone layer danger was "not very significant".^[96]

It was after being confronted with these results that they "chanced" upon the notion, as "an afterthought"^[95] of nuclear detonations igniting massive fires everywhere and most crucially, the smoke from these conventional fires, then going on to absorb sunlight and with that surface temperatures were likely to plummet.^[97] In early 1982 the two colleagues circulated a draft paper with the first suggestions of alterations in short-term climate from fires, presumed to occur following a nuclear war.^[71] Later in the same year, the special issue of Ambio devoted to the possible environmental consequences of nuclear war by Crutzen and Birks was titled "Twilight at Noon" and largely anticipated the nuclear winter hypothesis.^[98] The paper which looked into fires and their climatic effect discussed particulate matter from large fires, nitrogen oxide, ozone depletion and the effect of nuclear twilight on agriculture. Crutzen and Birks' calculations suggested that smoke particulates 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 this darkness persisting "for as long as the fires" burned, which was assumed to be many weeks, with 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."^[98] A policy implication of their work was that a successful nuclear decapitation strike could have severe climatic consequences for the perpetrator.

After reading a paper by N.P.Bochkov and E.I.Chazov, ^[99] published in the edition of Ambio that carried Crutzen and Birks’s paper Twilight at Noon, Soviet atmospheric scientist Georgy Golitsyn applied his research on Mars dust storms to soot in the Earth's atmosphere. The origin and application of these influential martian dust storm models in nuclear winter research has a history beginning in 1971,^[100] when the Soviet Mars 2 spacecraft arrived at the red planet and observed a global dust cloud. The orbiting instruments together with the Mars 3 lander determined that the surface of the red-planet was considerably colder than temperatures at the top of the upper dust cloud. Following these observations, Golitsyn received 2 telegrams from the, later to become famous US scientist Carl Sagan(an astronomer), which asked Golitsyn to "explore the understanding and assessment of this phenomenon." Golitsyn recounts that it was around this time that he had "proposed a theory to explain how (martian) dust may be formed and how it may reach global proportions."^[101]

In the same year Alexander Ginzburg,^[102] an employee in Golitsyn's institute, developed a model of dust storms that included a "simple equation" that described the cooling phenomenon on Mars. A dust cooling model that Golitsyn felt would be applicable to soot after he read the 1982 "Swedish magazine dedicated entirely to the effects of a hypothetical nuclear war between the USSR and the USA." In which specifically contained the discussion of the fires and smoke that would spread over the planet.^[103] Golitsyn would use Ginzburg's largely unmodified dust-cloud model with soot assumed as the aerosol in the model instead of soil dust and in an identical fashion to the results returned, when computing dust-cloud cooling in the Martian atmosphere, the planet cooled drastically while the cloud high above the planet would be heated as a result. Golitsyn presented his intent to publish this martian derived earth-analog model to the Andropov formed Committee of Soviet Scientists in Defence of Peace Against the Nuclear Threat in May 1983, an organization that Golitsyn would later be appointed a position of vice-chairman of.^[104] In September 1983 he published this first computer model on the nascent "nuclear winter" effect in the widely read Herald of the Russian Academy of Sciences.^[105]

On 31 October 1982 Golitsyn and Ginsburg's model and results were presented at the Conference on ”The World after Nuclear War”, hosted in Washington, D.C..^[106]

Both Georgy Golitsyn,^[107] and Carl Sagan^[108] had been interested in the cooling on the dust storms on the planet Mars in the years preceding their focus on "nuclear winter".

After the publication of Twilight at Noon in 1982,^[109] the so-called TTAPS team (named for its participants, Richard P. Turco, Owen Toon, Thomas P. Ackerman, James B. Pollack and Carl Sagan) say that they began the process of doing a 1-dimensional computational modeling study of the atmospheric consequences of nuclear war/soot in the stratosphere, though they would not publish a Science paper until late December 1983.^[110] The phrase "nuclear winter" was coined by Turco just prior to publication.^[111] In this early paper, TTAPS used assumption based estimates on the total smoke and dust emissions that would result from a major nuclear exchange, and with that, began analyzing the subsequent effects on the atmospheric radiation balance and temperature structure as a result of this quantity of assumed smoke. To compute dust and smoke effects, 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.

Interest in the environmental effects of soot/"nuclear war" however had continued in the Soviet Union after Golitsyn's September paper, with Vladimir Alexandrov and G. I. Stenchikov also publishing a paper in December 1983 on the climatic consequences , although in contrast to the contemporary TTAPS paper, this paper was based on simulations with a three-dimensional global circulation model.^[48] (Two years later Alexandrov disappeared under mysterious circumstances.) Richard Turco and Starley L. Thompson were critical of the Soviet research. Turco called it "primitive" and Thompson said it used obsolete US computer models.^[109] Later they were to rescind these "harsh" criticisms and instead applauded Alexandrov's pioneering work, saying that the Soviet model shared the weaknesses of all the others.^[112]

In 1984 the World Meteorological Organization(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 – 1–7011200000000000000♠2×10¹⁴ g being most likely, with a range of 0.2–7011640000000000000♠6.4×10¹⁴ g (NAS; TTAPS assumed 7014225000000000000♠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.^[113]

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 produced similar results: temperature drops of about 20 °C, though with regional variations.^[114]

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 effects of the post-war cooling to the direct deaths from explosions.

1990

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:^[115]

First 1 to 3 months:

• 10 to 25% of soot injected is immediately removed by precipitation, while the rest is transported over the globe in 1 to 2 weeks
• SCOPE figures for July smoke injection:
  • 22 °C drop in mid-latitudes
  • 10 °C drop in humid climates
  • 75% decrease in rainfall in mid-latitudes
  • Light level reduction of 0% in low latitudes to 90% in high smoke injection areas
• SCOPE figures for winter smoke injection:
  • Temperature drops between 3 and 4 °C

Following 1 to 3 years:

• 25 to 40% of injected smoke is stabilised in atmosphere (NCAR). Smoke stabilised for approximately 1 year.
• Land temperatures of several degrees below normal
• Ocean surface temperature between 2 and 6 °C
• Ozone depletion of 50% leading to 200% increase in UV radiation incident on surface.

Kuwait wells in the first Gulf War

The Kuwaiti oil fires were not just limited to burning oil wells, one of which is seen here in the background, but burning "oil lakes", seen in the foreground, also contributed to the smoke plumes, particularly the sootiest/blackest of them.^[116]

Smoke plumes from a few of the Kuwaiti Oil Fires on April 7, 1991. The plume boundaries/the maximum assumed extent of the combined plumes from over six hundred fires during the period of February 15 – May 30, 1991, are available.^[116][117] Only about 10% of all the fires, mostly corresponding with those that originated from "oil lakes" produced pure black soot filled plumes, 25% of the fires emitted white to grey plumes, while the remaining emitted plumes with colors between grey and black.^[116]

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.^[118] 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,^[119] 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 effects of "sub-freezing" temperatures as a result of the Iraqis going through with their threats of igniting 300 to 500 pressurized oil wells that could subsequently burn for several months.^{[118][120][121]}

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 effects 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 effects 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."^[122] 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 Singer's narrative being closer to what transpired, with the comparatively minimal atmospheric effects remaining limited to the Persian Gulf region, with smoke plumes, in general,^[116] lofting to about 10,000 feet (3,000 m) and a few times as high as 20,000 feet (6,100 m).^[123][124]

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."^[125]

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 effects in Asia and possibly the Northern Hemisphere as a whole.^[126]

The atmospheric scientist tasked with studying the atmospheric effect 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."^[127]

Hobbs 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.^[128][129]

Pre-war claims of wide scale, long-lasting, and significant global environmental effects were thus not borne out, and found to be significantly exaggerated by the media and speculators,^[130] 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.^[131]

This satellite photo of the south of Britain shows black smoke from the 2005 Buncefield fire, a series of fires and explosions involving approximately 250,000,000 litres of fossil fuels. The plume is seen spreading in two main streams from the explosion site at the apex of the inverted 'v'. By the time the fire had been extinguished the smoke had reached the English Channel. The orange dot is a marker, not the actual fire. Although the smoke plume was from a single source, and larger in size than the individual oil well fire plumes in Kuwait 1991, the Buncefield smoke cloud remained out of the stratosphere.

The idea of oil well and oil reserve smoke pluming to the stratosphere 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 more of a possible contributor than smoke from cities, as the smoke from oil has a higher ratio of black soot, thus absorbing more sunlight.^[98][110] Hobbs compared the papers' assumed "emission factor" or soot generating efficiency from ignited oil pools and found, upon comparing to measured values from oil pools at Kuwait, which were the greatest soot producers, the emissions of soot assumed in the nuclear winter calculations are still "too high".^[129] Following the results of the Kuwaiti oil fires being in disagreement with the core nuclear winter promoting scientists, the 1990s nuclear winter papers generally attempted to distance themselves from suggesting oil well and reserve smoke will reach the stratosphere.

In 2007, a nuclear winter study, which will be discussed later, 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 like some forest fires can lift smoke into the stratosphere, and this is supported by recent evidence that it occurs far more often than previously thought.^{[132][133][134][135][136][137][138]} 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]^[139] conducted detailed, high-resolution smoke plume simulations with the RAMS regional climate model [e.g., Miguez-Macho et al., 2005]^[140] 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].^[141]

However the above simulation notably contained the assumption that no dry and wet deposition/rain would occur.^[142]

Recent modeling

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.^[143][144] However far from being "new", the very same beginning to "significant" nuclear winter effects, was in the mid 1980s models, similarly regarded to have been a threat from a total of 100 or so city firestorms.^[145][146]

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.

2007 study on global nuclear war

A study published in the Journal of Geophysical Research in July 2007,^[147] "Nuclear winter revisited with a modern climate model and current nuclear arsenals: Still catastrophic consequences",^[148] 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."

2014

In 2014, Michael J. Mills (at the US National Center for Atmospheric Research, NCAR), Owen B. Toon (of the original TTAPS team), Julia Lee-Taylor, and Alan Robock published "Multi-decadal global cooling and unprecedented ozone loss following a regional nuclear conflict" in the journal Earth's Future.^[149] 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.

Criticism and debate

The four major, largely independent underpinnings, that the nuclear winter concept has and continues to receive criticism over, are regarded as,^[150] first in the fire domain; would cities readily firestorm and if so, how much soot would be generated. Secondly, atmospheric longevity; would the quantities of soot assumed in the models remain in the atmosphere for as long as projected or would far more soot precipitate as black rain much sooner. Third, timing of events; how realistic is it to start the firestorms or "war" modelling in the month of May/summer, which almost all US-Soviet winter papers assume, so as to depict the maximum possible cooling results. Lastly, the issue of darkness or opacity; how much light-blocking effect would the assumed quantity of soot reaching the atmosphere have.^[150]

While the highly popularized initial 1983 TTAPS 1-dimensional model forecasts were widely reported and criticized in the media, in part because every later model predicts far less of its "apocalyptic" level of cooling,^[151] most models continue to suggest that some deleterious global cooling would still result, under the assumption that a large number of fires occurred in the spring or summer.^[152][153] Starley L. Thompson's less primitive mid-1980s 3-Dimensional model, which notably contained the very same general assumptions, led him to coin the term "nuclear autumn" to more accurately describe the climate results of the soot in this model, with an on camera interview in which he dismisses the earlier "apocalyptic" models.^[154]

A major criticism of the assumptions that continue to make these model results possible appeared in the 1987 book (NWSS) Nuclear War Survival Skills, a civil defense manual by Cresson Kearny for the Oak Ridge National Laboratory.^[155] According to the 1988 publication An assessment of global atmospheric effects of a major nuclear war, Kearny's criticisms were directed at the excessive amount of soot that the modelers assumed would reach the stratosphere, with Kearny citing a Soviet study that modern cities would not burn as firestorms, as most flammable city items would be buried under [non combustible] rubble and that the TTAPs study included a massive overestimate on the size and extent of non-urban wildfires that would result from a nuclear war.^[156] The TTAPs authors responded that, amongst other things, they did not believe target planners would intentionally blast cities into rubble, but instead argued fires would begin in relatively undamaged suburbs when nearby sites were hit, and partially conceded his point about non-urban wildfires.^[157] Dr. Richard D. Small, director of thermal sciences at the Pacific-Sierra Research Corporation similarly disagreed strongly with the model assumptions, in particular the 1990 update by TTAPs that argues that some 5,075 teragrams (trillions of grams) of material would burn in a total US-Soviet nuclear war, as analysis by Small of blueprints and real buildings returned a maximum of 1,475 teragrams of material could be burned, "assuming that all the available combustible material was actually ignited".^[150]

Although Kearny was of the opinion that future more accurate models would "indicate there will be even smaller reductions in temperature", including future potential models that did not so readily accept firestorms would occur as dependably as nuclear winter modellers assume, in NWSS Kearny did summarize the comparatively moderate cooling estimate of no more than a few days,^[155] from the 1986 Nuclear Winter Reappraised model^[158][159] by Starley Thompson and Stephen Schneider. This was done in an effort to convey to his readers that contrary to the popular opinion at the time, in the conclusion of these two climate scientists, "on scientific grounds the global apocalyptic conclusions of the initial nuclear winter hypothesis can now be relegated to a vanishing low level of probability."^[155]

However while a 1988 article by Brian Martin in Science and Public Policy^[152] states that although Nuclear Winter Reappraised concluded the US-Soviet "nuclear winter" would be much less severe than originally thought, with the authors describing the effects more as a "nuclear autumn", other statements by Thompson and Schneider^[160][161] show that they "resisted the interpretation that this means a rejection of the basic points made about nuclear winter". In the Alan Robock et al. 2007 paper they write that "because of the use of the term 'nuclear autumn' by Thompson and Schneider [1986], 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]."^[147][148] In 2007 Schneider expressed his tentative support for the cooling results of the limited nuclear war (Pakistan and India) analyzed in the 2006 model 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." As "anything that you can do to discourage people from thinking that there is any way to win anything with a nuclear exchange is a good idea."^[162]

The contribution of smoke from the ignition of live non-desert vegetation, living forests, grasses and so on, near to many missile silos is a source of smoke originally assumed to very large in the initial Twilight at Noon paper and also found in the popular TTAPs publication. However this assumption was examined by Bush and Small in 1987 and they found that the burning of live vegetation could only conceivably contribute very slightly to the estimated total "nonurban smoke production".^[163] With the vegetations potential to sustain burning only probable if it is within a radius or two from the surface of the nuclear fireball, which is at a distance that would also experience extreme blast winds that would influence any such fires.^[164] This reduction in the estimate of the non-urban smoke hazard is supported by the earlier preliminary Estimating Nuclear Forest Fires publication of 1984,^[165] and by the 1950-60s in-field examination of surface-scorched, mangled but never burnt-down tropical forests on the surrounding islands from the shot points in the Operation Castle,^[166] and Operation Redwing,^[167] test series.

During the Operation MeetingHouse firebombing of Tokyo on 9–10 March 1945, 1,665 tons(1.66 kiloton) of incendiary and high-explosive bombs in the form of bomblets were dropped on the city, causing the destruction of over 10,000 acres of buildings — 16 square miles (41 km²), the most destructive and deadliest bombing operation in history.^[168][169]

While in comparison, the first nuclear bombing in history used a 16-kiloton nuclear bomb, thus approximately 10 times more energy was delivered to the city of Hiroshima than delivered onto Tokyo, yet due in part to the comparative inefficiency of larger bombs,^{[note 1][170]} a much smaller area of building destruction occurred when contrasted with the results from Tokyo, only 4.5 square miles (12 km²) of Hiroshima was destroyed by blast, fire, and firestorm effects.^[171] Similarly, Major Cortez F. Enloe, a surgeon in the USAAF who worked with the United States Strategic Bombing Survey (USSBS), noted that the even more energetic 22-kiloton nuclear bomb dropped on Nagasaki did not result in a firestorm and thus did not do as much fire damage as the conventional airstrikes on Hamburg which in contrast, did generate a firestorm.^[172] Thus, the question of; can a city firestorm, has nothing to do with the size or type of bomb dropped, but solely depends on the density of fuel present in the city. Moreover, it has been observed that firestorms are not likely in areas where modern buildings(bricks,concrete) have totally collapsed, by comparison, Hiroshima, and Japanese cities in general in 1945, had then consisted of mostly densely-packed "flimsy" wooden houses along with the common use of Shoji paper sliding walls.^[171][173] The fire hazard construction practices present in cities that have historically firestormed, are now illegal in most countries for general safety reasons and therefore cities with firestorm potential are far rarer than was common at the time of WWII.

In a paper by the United States Department of Homeland Security finalized in 2010, fire experts stated that due to the nature of modern city design and construction, with the US serving as an example, a firestorm is unlikely after a nuclear detonation in a modern city.^[174] This is not to say that fires won't occur over a large area after a detonation, but that the fires would not coalesce and form the all important stratosphere punching firestorm plume that the nuclear winter papers require as a prerequisite assumption in their climate computer models. The nuclear bombing of Nagasaki for example, did not produce a firestorm.^[175] This was similarly noted as early as 1986-88, when the assumed quantity of fuel "mass loading" (the amount of fuel per square meter) in cities underpinning the winter models was found to be too high and intentionally creates heat fluxes that lofts smoke into the lower stratosphere, yet assessments "more characteristic of conditions" to be found in real-world modern cities, had found that the fuel loading, and hence the heat flux that would result from efficient burning, would rarely loft smoke much higher than 4 km.^[176]

Russell Seitz, Associate of the Harvard University Center for International Affairs, argues that the winter models' assumptions give results which the researchers want to achieve and is a case of "worst-case analysis run amok".^[177] In September 1986 Seitz published Siberian fire as “nuclear winter” guide in the journal Nature in which he investigated the 1915 Siberian fire which likewise started in the early summer months and which was caused by the worst drought in the regions recorded history. The fire ultimately devastated the region with the worlds largest boreal forest, the size of Germany and while approximately 8 degrees Celsius of daytime summer cooling occurred under the smoke clouds during the weeks of burning, no increase in potentially devastating agricultural night frosts occurred.^[178] Following his investigation into the Siberian fire of 1915, Seitz criticized the "nuclear winter" model results for being based on successive worst-case events: “The improbability of a string of 40 such coin tosses coming up heads approaches that of a pat royal flush. Yet it was represented as a "sophisticated one-dimensional model"—a usage that is oxymoronic, unless applied to [the British model Lesley Lawson] Twiggy.”^[179]

Seitz cited Carl Sagan, adding an emphasis: "In almost any realistic case involving nuclear exchanges between the superpowers, global environmental changes sufficient to cause an extinction event equal to or more severe than that of the close of the Cretaceous when the dinosaurs and many other species died out are likely.” Seitz comments: “The ominous rhetoric italicized in this passage puts even the 100 megaton[/the original 100 city firestorm] scenario … on a par with the 100 million megaton blast of an asteroid striking the Earth. This [is] astronomical mega-hype …”^[179] Seitz concludes:

As the science progressed and more authentic sophistication was achieved in newer and more elegant models, the postulated effects headed downhill. By 1986, these worst-case effects had melted down from a year of arctic darkness to warmer temperatures than the cool months in Palm Beach! A new paradigm of broken clouds and cool spots had emerged. The once global hard frost had retreated back to the northern tundra. Mr. Sagan's elaborate conjecture had fallen prey to Murphy's lesser-known Second Law: If everything MUST go wrong, don't bet on it.^[179]

Seitz's opposition caused the proponents of nuclear winter to issue responses in the media, and while both sides made important points, they were largely incapable of collaborating as the proponents believed it was simply necessary to show only the possibility of climatic catastrophe, often a worst-case scenario, while opponents insisted that to be taken seriously, nuclear winter should be shown as likely under "reasonable" scenarios.^[180] One of these areas of contention, as elucidated by Lynn R. Anspaugh, is upon the question of which season should be used as the backdrop for the US-USSR war models, as most models choose the summer in the Northern Hemisphere as the start point to produce the maximum soot lofting and therefore eventual winter effect, whereas it has been pointed out that if the firestorms occurred in the fall or winter months, when there is much less intense sunlight to loft soot into a stable region of the stratosphere, the magnitude of the cooling effect from the same number of firestorms as ignited in the summer models, would be negligible according to a January model run by Covey et al.,^[181] and an issue that Schneider conceded in 1990, "a war in late fall or winter would have no appreciable [cooling] effect".^[150]

John Maddox, editor of the journal Nature, issued a series of skeptical comments about nuclear winter studies during his tenure,^[182][183] being a long-time critic of environmental doomsdayism,^[177] his critical analysis of the hypothesis is regarded to have withstood the test of time.^[184] Similarly S. Fred Singer was a long term vocal critic of the hypothesis in the journal and in televised debates with Carl Sagan.^{[185][186][187]} In a 2011 response to the more modern papers on the hypothesis, Russell Seitz published a comment in Nature challenging Alan Robock's claim that there has been no real scientific debate about the 'nuclear winter' concept.^[188] As MIT meteorologist Kerry Emanuel similarly wrote a review in nature that the winter concept is “notorious for its lack of scientific integrity” due to the unrealistic estimates selected for the quantity of fuel likely to burn, the impercise GCM/global circulation models used, and ends by stating that the evidence of other models, point to substantial scavenging of the smoke by rain.^[189] Emanuel would also make an "interesting point" about questioning proponent's objectivity when it came to strong emotional or political issues that they hold.^[190] Seitz also contends that many others are reluctant to speak out for fear of being stigmatized as closet Dr. Strangeloves, physicist Freeman Dyson of Princeton for example stated "It's an absolutely atrocious piece of science, but I quite despair of setting the public record straight."^[191] Stephen Schneider for example was labelled a "fascist" for writing the critical paper, "Nuclear Winter Reappraised" according to Rocky Mountain News.^[155]

Lynn R. Anspaugh also expressed frustration that although a managed (Chapleau, Ontario) forest fire in Canada on 3 August 1985 is said to have been lit by proponents of nuclear winter, with the fire potentially serving as an opportunity to do some basic measurements of the optical properties of the smoke and smoke-to-fuel ratio, which would have helped refine the estimates of these critical model inputs, the proponents did not indicate that any such measurements were made.^[192] Peter V. Hobbs, who would later successfully attain funding to fly into and sample the smoke clouds from the Kuwait oil fires in 1991, also expressed frustration that he was denied funding to sample the Canadian, and other forest fires in this way.^[193] Richard Turco (of TTAPs fame) simply wrote a 10-page memorandum with information derived from his notes and some satellite images, that the smoke plume reached 6 km in altitude.^[194]

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 smoke's 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 could be negligible, minor or massive.^[195] The assumed optical properties for black carbon in more recent nuclear winter papers (2006) are still "based on those assumed in earlier nuclear winter simulations".^[196]

William R. Cotton Professor of Atmospheric Science at Colorado State University, specialist in cloud physics modeling and co-creator of the highly influential,^[197][198] and previously mentioned RAMS atmosphere model, had in the 1980s, worked on soot rain-out models^[199] and supported the predictions made by his own and other nuclear winter models,^[200] but has since reversed this position according to a book co-authored by him in 2007, stating that, amongst other systematically examined assumptions; far more rain out/wet deposition of soot will occur than is assumed in modern papers on the subject, "We must wait for a new generation of GCMs to be implemented to examine potential consequences quantitatively" and revealing that in his experience "nuclear winter was largely politically motivated from the beginning".^[26][201]

Policy implications

During the Cuban Missile Crisis, Fidel Castro and Che Guevara called on the USSR to launch a nuclear first strike against the US in the event of a US invasion of Cuba. As late as the early 1980s, Fidel Castro was pressuring the Kremlin to adopt a harder line against Washington, even arguing for the for the admissibility of using nuclear weapons. Castro reversed his position on nuclear first use after being briefed by Soviet officials in 1985 about the ecological effect on Cuba of nuclear strikes on the United States.^[202] 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 the nationwide state-controlled television station in the country.^[203][204] 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.^[204]

United States and Soviet Union/Russia nuclear stockpiles. The effects of trying to make others believe the results of the models on nuclear winter, does not appear to have decreased either country's nuclear stockpiles in the 1980s,^[205] only the failing Soviet economy and the dissolution of the country between 1989–91 which marks the end of the Cold War and with it the relaxation of the "arms race", appears to have had an effect. The effects of the electricity generating Megatons to Megawatts program can also be seen in the mid 1990s, continuing the trend in Russian reductions. A similar chart focusing solely on quantity of warheads in the multi-megaton range is also available.^[206] Moreover, total deployed US & "Russian" strategic weapons increased steadily from 1983 until the Cold War ended.^[207]

In a 2012 "Bulletin of the Atomic Scientists" feature, Alan Robock and Owen Toon, who had routinely mixed their disarmament advocacy into the conclusions of their "nuclear winter" papers,^[8] argue in the political realm that the hypothetical effects of nuclear winter necessitates that the doctrine they assume is active in Russia and US, "mutually assured destruction" (MAD) should instead be replaced with their own "self-assured destruction" (SAD) concept,^[208] because, regardless of whose cities burned[firestormed], the effects of the resultant nuclear winter that they advocate, would be, in their view, catastrophic. In a similar vein, in 1989 Carl Sagan and colleague Richard Turco wrote a policy implications paper that appeared in AMBIO that suggests that as nuclear winter is a "well-established prospect", both superpowers should jointly reduce their nuclear arsenals to "Canonical Deterrent Force" levels of 100–300 individual warheads each, such that in "the event of nuclear war [this] would minimize the likelihood of [extreme] nuclear winter."^[209]

An originally classified 1984 US intelligence agency report states that in both the preceding 1970s and 80s, the Soviet and US military were already following the "existing trends" in warhead miniaturization, of higher accuracy and lower yield nuclear warheads,^[210] a prime example being the most numerous warheads in the US arsenal, the 50 kt(kiloton) W68 and 100 kt W76. This trend towards miniaturization, enabled by advances in inertial guidance and accurate GPS navigation etc., was motivated by a multitude of factors, namely the desire to leverage the physics of equivalent megatonnage that miniaturization offered; of freeing up space to fit more MIRV warheads and decoys on each missile. Alongside the desire to still destroy hardened targets but while reducing the severity of fallout collateral damage depositing on neighboring, and potentially friendly, countries. As it relates to the likelihood of nuclear winter, the range of potential thermal radiation ignited fires was already reduced with miniaturization. For example, the most popular nuclear winter paper, the 1983 "TTAPS" paper, had described a 3000 Mt counterforce attack on ICBM sites with each individual warhead being approximately akin to the W53(9 megaton); however not long after publication, Michael Altfeld of Michigan State University and political scientist Stephen Cimbala of Pennsylvania State University argued that the then already developed and deployed smaller, more accurate warheads(e.g W76), together with lower detonation heights, could produce the same counterforce strike with a total of only 3 Mt of energy being expended. They continue that, if the nuclear winter models prove to be representative of reality, then far less climatic-cooling would occur, even if firestorm prone areas existed in the target list, as lower fuzing heights such as surface bursts, would also limit the range of the burning thermal rays due to terrain masking and shadows cast by buildings,^[211] while also temporarily lofting far more radioactive soil into the atmosphere/localized fallout when compared to airburst fuzing - the standard mode of employment against un-hardened targets.

The 1951 Shot Uncle of Operation Buster-Jangle, had a yield about a tenth of the 13 to 16 kt Hiroshima bomb. 1.2 kilotons,^[212] and was detonated 5.2 m (17 ft) beneath ground level.^[213] The explosion resulted in a cloud that rose to 3.5 km "11,500 ft".^[214] The resulting crater was 260 feet wide and 53 feet deep.^[215] The yield is similar to that of an Atomic Demolition Munition. Altfeld & Cimbala argue that true belief in nuclear winter might lead nations towards building greater arsenals of weapons of this type.^[216] However, despite being complicated due to the advent of Dial-a-yield technology, data on these low yield nuclear weapons suggests that they now make up no less than a tenth of the arsenal of the US and Russia, and the fraction of the stockpile that they occupy has diminished since the 1970-90s, not grown.^[217] A factor in this is that very thin devices with yields approximately around 1 kiloton of energy are nuclear weapons that make very inefficient use of their nuclear materials, e.g two-point implosion. Thus a more psychologically detering higher efficiency/higher yield device, can instead be constructed from the same mass of fissile material.

This logic is similarly reflected in the aforementioned 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.^[210] Therefore, as a consequence of attempting to limit the target fire hazard by reducing the range of thermal radiation with fuzing for surface and sub-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.^[211][218]

Altfeld and Cimbala also argued that belief in the possibility of nuclear winter would actually make nuclear war more likely, contrary to the views of Sagan and others, because it would serve yet further motivation to follow the existing trends, towards the development of more accurate, and even lower explosive yield, nuclear weapons.^[219] As the winter hypothesis suggests that the replacement of the then Cold War viewed strategic nuclear weapons in the multi-megaton yield range, with weapons of explosive yields closer to tactical nuclear weapons, such as the Robust Nuclear Earth Penetrator, would safeguard against the nuclear winter potential. Tactical nuclear weapons, on the low end of the scale have yields that overlap with large conventional weapons, and are therefore often viewed "as blurring the distinction between conventional and nuclear weapons", making the prospect of using them "easier" in a conflict.^[220][221]

Soviet exploitation

In an interview in 2000, with Mikhail Gorbachev(the Soviet leader from 1985–91), the following statement was posed to him: "In the 1980s, you warned about the unprecedented dangers of nuclear weapons and took very daring steps to reverse the arms race," With Gorbachev replying "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."^[222]

However a 1984 US Interagency Intelligence Assessment expresses 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 Soviet officials did begin to take nuclear winter seriously, it would probably make them 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.^[223] 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.^[210]

In 1985 Time magazine noted "the suspicions of some Western scientists that the nuclear winter hypothesis was promoted by Moscow to give anti-nuclear groups in the U.S. and Europe some fresh ammunition against America's arms buildup."^[224]

In 1986, the Defense Nuclear Agency document An update of Soviet research on and exploitation of Nuclear winter 1984–1986 charted the minimal [public domain] research contribution on, and Soviet propaganda usage of, the nuclear winter phenomenon.^[225]

There is some doubt as to when the Soviet Union began modelling fires and the atmospheric effects of nuclear war. Former Soviet intelligence officer Sergei Tretyakov claimed that, under the directions of Yuri Andropov, the KGB invented the concept of "nuclear winter" in order to stop the deployment of NATO Pershing II missiles. They are said to have distributed to peace groups, the environmental movement and the journal Ambio disinformation based on a faked "doomsday report" by the Soviet Academy of Sciences by Georgii Golitsyn, Nikita Moiseyev and Vladimir Alexandrov concerning the climatic effects of nuclear war.^[226] Although it is accepted that the Soviet Union exploited the nuclear winter hypothesis for propaganda purposes,^[227] Tretyakov's inherent claim that the KGB funnelled disinformation to AMBIO, the journal in which Paul Crutzen and John Birks published the 1982 Twilight at Noon paper, has not been corroborated as of 2009.^[228] In an interview in 2009, conducted by the National Security Archive, Vitalii Nikolaevich Tsygichko; a Senior Analyst at the Soviet Academy of Sciences and military mathematical modeler, stated that Soviet military analysts were discussing the idea of "nuclear winter" years before U.S. scientists, although they did not use that exact term.^[229]

Within the 2011 Federal Bureau of Investigation(FBI) publication, The Targeting of Sensitive, Proprietary, and Classified Information on Campuses of Higher Education, the unnamed author presents Tretyakov's nuclear winter claim, then notes that "Disinformation may be blatant deception or small fabricated kernals in a large milieu of reliable facts" and that it is important to science, where research is often based on previous research, that all research is based on correct data, or many subsequent conclusions could be inaccurate as well.^[230]

Mitigation techniques

A number of solutions have been proposed to mitigate the potential harm of a nuclear winter if one appears inevitable; with the problem being attacked at both ends, from those focusing on preventing the growth of fires and therefore limiting the amount of smoke that reaches the stratosphere in the first place, to food production under dimmed skies with the assumption that the very worst-case analysis results of the nuclear winter models prove accurate and no other mitigation strategies are fielded.

Fire control

In a report from 1967, techniques included various methods of applying liquid nitrogen, dry ice, and water to nuclear-caused fires.^[231] The report considered attempting to stop the spread of fires by creating firebreaks by blasting combustible material out of an area, possibly even with nuclear weapons, along with the use of preventative Hazard reduction burns. According to the report, one of the most promising techniques investigated was initiation of rain from seeding of mass-fire thunderheads and other clouds passing over the developing, and then steady-state, firestorm.

Producing food without sunlight

Possibilities include natural-gas-digesting bacteria^[232] or mushrooms that can grow directly on wood without sunlight.^[233] Another example is that cellulosic biofuel production typically already creates sugar as an intermediate product.^[234]

Large-scale food stockpiling

The minimum annual global wheat storage is approximately 2 months.^[235] To feed everyone despite nuclear winter, years of food storage prior to the event has been proposed.^[236] While the suggested masses of preserved food would likely never get used as a nuclear winter is comparatively unlikely to occur, the stockpiling of food would have the positive result of ameliorating the effect of the far more frequent disruptions to regional food supplies caused by lower-level conflicts and droughts. There is however the danger that if a sudden rush to food stockpiling occurs without the buffering effect offered by Victory gardens etc., it may exacerbate current food security problems by elevating present food prices.

Climate engineering

Despite the name "nuclear winter", nuclear events are not necessary to produce the modeled climatic effect.^[22][237] In an effort to find a quick and cheap solution to the global warming projection of at least two degrees of surface warming as a result of the doubling in CO2 levels within the atmosphere, through solar radiation management (a form of climate engineering) the underlying nuclear winter effect has been looked at as perhaps holding potential. Besides the more common suggestion to inject sulfur compounds into the stratosphere to approximate the effects of a volcanic winter, the injection of other chemical species such as the release of a particular type of soot particle, to create minor "nuclear winter" conditions, has also been proposed by Paul Crutzen and others.^[238][239] According to the threshold/minor "nuclear winter" computer models,^[144][240] if one to five teragrams of firestorm-generated soot^[241] is injected into the low stratosphere, it is modeled, through the anti-greenhouse effect, to heat the stratosphere but cool the lower troposphere and produce 1.25 °C cooling for two to three years; after 10 years, average global temperatures would still be 0.5 °C lower than before the soot injection.^[6]

Potential climatic precedence

An animation depicting a massive asteroid–Earth impact and subsequent impact crater formation. The asteroid connected with the extinction of the Dinosaurs/Cretaceous–Paleogene extinction event released an estimated energy of 100 teratonnes of TNT (420 ZJ).^[242] corresponding to 100,000,000 Mt of energy, roughly 10,000 times the maximum combined arsenals of the US and Soviet Union in the Cold War.^[243] This is hypothesized to have produced sufficient ground-energy coupling to have caused severe mantle plume (volcanism) at the antipodal point (the opposite side of the world).^[244]

Similar climatic effects to "nuclear winter" followed historical supervolcano eruptions, which plumed sulfate aerosols high into the stratosphere, with this being known as a volcanic winter.^[245]

Similarly, extinction-level comet and asteroid impacts are also believed to have generated impact winters by the pulverization of massive amounts of fine rock dust. This pulverized rock can also produce "volcanic winter" effects, if sulfate-bearing rock is hit in the impact and lofted high into the air,^[246] and "nuclear winter" effects, with the heat of the heavier rock ejecta igniting regional and possibly even global forest firestorms.^[247][248]

This global "impact firestorms" hypothesis, initially supported by Wolbach, Melosh and veteran nuclear winter modeler Owen Toon, suggests that as a result of massive impact events, the small sand-grain-sized ejecta fragments created can meteorically re-enter the atmosphere forming a hot blanket of global debris high in the air, potentially turning the entire sky red-hot for minutes to hours, and with that, burning the complete global inventory of above-ground carbonaceous material, including rain forests.^[249][250] This hypothesis is suggested as a means to explain the severity of the Cretaceous–Paleogene extinction event, as the earth impact of an asteroid about 10 km wide which precipitated the extinction is not regarded as sufficiently energetic to have caused the level of extinction from the initial impact's energy release alone.

The global "impact firestorms"/firestorm winter, however, has been questioned in more recent years (2003–2013) by Claire Belcher,^{[249][251][252]} Tamara Goldin^{[253][254][255]} and H. Jay Melosh, who had initially supported the hypothesis,^[256][257] with this re-evaluation being dubbed the "Cretaceous-Palaeogene firestorm debate" by Belcher.^[249]

Depending on the size of the meteor, it will either burn up high in the atmosphere or reach lower levels and explode in an air burst akin to the Chelyabinsk meteor of 2013, which approximated the thermal effects of a nuclear explosion.

The issues raised by these scientists in the debate are the perceived low quantity of soot in the sediment beside the fine-grained iridium-rich asteroid dust layer, if the quantity of re-entering ejecta was perfectly global in blanketing the atmosphere, and if so, the duration and profile of the re-entry heating, whether it was a high thermal pulse of heat or the more prolonged and therefore more incendiary "oven" heating,^[256] and finally, how much the "self-shielding effect" from the first wave of now-cooled meteors in dark flight contributed to diminishing the total heat experienced on the ground from later waves of meteors.^[249]

In part due to the Cretaceous period being a high-atmospheric-oxygen era, with concentrations above that of the present day. Owen Toon et al. in 2013 were critical of the re-evaluations the hypothesis is undergoing.^[250]

It will be difficult to successfully tease out the percentage contribution of the soot in this period's geological sediment record from living plants and fossil fuels present at the time,^[258] in much the same manner that the fraction of the material ignited directly by the meteor impact will be difficult to determine.

See also

• Doomsday device
• Younger Dryas impact hypothesis, a similarly controversial hypothesis that an impact event & fires triggered the last ice age.
• Impact winter
• Volcanic winter
• Krakatoa, 1883 eruption, which caused approximately 1 kelvin of global cooling for 2 years due to sulfate emissions.
• Year Without a Summer, 1815, created by a volcanic eruption in Tambora.
• Laki, 1783 eruption of an Icelandic volcano which produced continentally localized cooling for 1–2 years.
• Toba catastrophe theory, a controversial hypothesis that a volcanic winter produced by the eruption of a volcano in Toba, Indonesia, created a human population bottleneck approx 80,000 years ago.
• List of states with nuclear weapons
• Global dimming, global reduction in ground insolation, due to the atmospheric injection of aerosols from various sources.
• Dalton minimum, 1790 to 1830, a period of prolonged solar minimum activity, resulting in Earth receiving lower insolation values.
• Little ice age, a period of low temperatures from the sixteenth to the nineteenth centuries, partially overlapping with the Maunder Minimum of solar activity, 1645 to 1715.
• Nuclear famine

Documentaries

• On the 8th Day – Nuclear winter documentary (1984) filmed by the BBC and available on Internet video hosting websites; chronicles the rise of the hypothesis, with lengthy interviews of the prominent scientists who published the nascent papers on the subject.^[259]

Media

• The Cold and the Dark: The World after Nuclear War: A book co-authored by Carl Sagan in 1984 which followed his co-authoring of the TTAPS study in 1983.
• Threads: A 1984 docu-drama that Carl Sagan assisted in an advisory capacity.
• A Path Where No Man Thought: Nuclear Winter and the End of the Arms Race: A book authored by Richard P. Turco and Carl Sagan, published in 1990; it explains the nuclear winter hypothesis and, with that, advocates nuclear disarmament.
• Nuclear Winter is a mini documentary by Retro Report that looks at nuclear winter fears in today's world.

Notes

External links

• The Encyclopedia of Earth, Nuclear Winter Lead Author: Alan Robock. Last Updated: July 31, 2008
• Nuclear Winter Simulation Animation
• New studies of climatic consequences of regional nuclear conflict from Alan Robock, including links to new studies published in 2007.

References

Footnotes