Nuclear Winter Update Part 2
Chronology
“Nuclear Winter” is the term used to designate a particular kind of climate catastrophe which would very likely ensue as the result of an all-out nuclear war between the US and Russia or China. Although I have written about this topic before [1] - [3], my focus has mostly been on the consequences of a big war and not, for example a regional conflict, say between India and Pakistan. And also on technical details, and not history. Here, I'm altering my approach, and emphasizing history, with technical aspects playing a distinctly secondary role.
Human understanding of the various phenomena involved in bringing about a nuclear winter has developed over dozens of centuries, starting with the speculation by Plutarch that the eruption of Mount Etna in 44 BC caused the cool weather that led to crop failures in Rome and Egypt, an idea espoused by Ben Franklin to explain the exceptionally cold European winter of 1783-84 [4]. Those speculations were ratified scientifically in the twentieth century, not only by examining historical records of unusual cold spells following large volcanic eruptions, but also by direct observation of the stratospheric aerosols and their effects following the eruption of Mt. Pinatubo in 1991. It was then only natural to extrapolate to other gigantic explosions, namely surface bursts of nuclear weapons, which were also observed to transport ash and dust into the stratosphere. What follows is my reconstruction of the development of understanding of the nuclear winter phenomenon.
R.C. Manins' 1967 paper [5] reports that nuclear explosions with yields of at least 30 kilotons (kt) at mid- to high latitudes would inject debris into the stratosphere. He also calculated fire power levels required to inject smoke into the stratosphere. (The stratosphere boundary varies with latitude; it is significantly higher at low latitudes. Hence the need to specify latitude.)
In 1975 the National Research Council issued a report on long term global effects of a nuclear war[6], stating that the current understanding of climatic effects was insufficient to either predict or rule out long term damage. One page of the 213 page report was devoted to the topic.
The third edition of The Effects of Nuclear Weapons [7] was published in 1977. Based on World War 2 firestorm experiments at Hamburg, Dresden, Tokyo and Hiroshima, criteria for inducing a firestorm were given. These criteria remain in use. A Scientific American article by Lewis [8] brought the seriousness of long term effects of nuclear war to the public's attention, and motivated scientific investigations outside the nuclear weapons community.
In 1982 Crutzen and Birks published a very influential paper [9] in which they detailed the chemical processes in the atmosphere resulting from nuclear detonations, distinguishing those processes from the ones attendant to volcanic eruptions. Production of oxides of Nitrogen, ozone depletion, and smoke were discussed. They surmised that serious climatic consequences could result from a nuclear war.
The topic of nuclear winter emerged into the public sphere in 1983, first with the “TTAPS” paper [10] so-called due to the last name initials of its authors, then the article by Carl Sagan [11] that brought the topic to the public's attention. This forced the nuclear weapons establishment to react, resulting in another study by the NRC.
In 1984-85 the NRC report was issued [12] and followed up in short order by a report from the Secretary of Defense [13], which in turn triggered the Congressional hearings starring Carl Sagan that I referenced in [14]. The NRC report focused closely on the TTAPS paper, emphasizing uncertainties and limitations in both the modeling and underlying science, but concluded that the possibility of catastrophic climate damage could not be discounted, and therefore further research was warranted. The DoD report was largely an exercise in denial, with disingenuous statements regarding the targeting of civilian targets, i.e. cities. (Of course we would never target the citizens of Moscow, any more than the Russians would target the citizens of Arlington, VA. Any civilian casualties there would be unintended collateral damage from nuking the shit out of the Kremlin and Pentagon, respectively.) There were helpful suggestions for minimizing urban fires by using surface bursts rather than air bursts, never mind the immense increase in radioactive fallout. The list goes on; in short, the DoD refused to reconsider its nuclear posture. Congress was not amused, which was why Sagan was asked to testify.
Also in 1985 Haberle et al. published a paper in which the self-lofting of black carbon into the stratosphere was discussed [15]. Briefly, black carbon (bc) is the terminology for fine, dark soot particles with high carbon content. These particles are extremely efficient absorbers of sunlight, which causes them to heat up. They then radiate this heat away in the form of infrared radiation, warming the surrounding air. Warm air rises, and carries the tiny bc particles with it, right up into the stratosphere, where they can remain for months to years. Although self-lofting was not mentioned in the TTAPS paper it found its way into [13], though its implications were either not recognized or ignored.
Then, for more than twenty years nothing happened in the public sphere. In the scientific community, however, things did not come to a halt. Advances in computing power enabled, and the looming global warming catastrophe motivated, development of ever more powerful and accurate climate models. Despite the best efforts of climate change deniers like George W. Bush to impede it, the capability for environmental monitoring via satellites grew.
Starting in about 1980, papers such as [16] -[18] started appearing in the scientific literature documenting satellite observations of smoke from forest fires being lofted into the stratosphere, even to altitudes more than 20 km above the tropopause (the troposphere – stratosphere boundary). What this means is that firestorms in dense urban areas are not the only possible contributors to stratospheric bc in the aftermath of a nuclear war.
The year 2007 saw the beginning of the current round of nuclear winter papers, these based on coupled, modern climate modeling codes. The initial papers in the series, with lead authors Robock [19] and Toon [20]-[21] explored the aftermath of a regional nuclear war between India and Pakistan, involving 50 ea, 15 kt nuclear weapons used by each side. For the analysis, it was assumed that the war would result in the injection of 5 MT (million (metric) tons) of soot in the upper troposphere or mixed between the upper troposphere and the lower stratosphere, with the model then predicting the evolution over time. Multiyear persistence in the stratosphere was predicted, with consequent shortening of the growing season by 10-20 days over large portions of the northern hemisphere in the first year.
In 2018 Reisner and colleagues published the results of a study that appeared to contradict the aforementioned work [22]. Their analysis modeled target firestorm development in detail using the LANL in-house HIGRAD and FIRETEC codes, developed to model wildland [sic] fire behavior [23]. Atmospheric aspects used the same climate code as was used by Robock, Toon and their colleagues. When fed the injection quantity used by Robock et al. Reisner's group obtained “similar” results. [Why not identical? See below.] Publication of their paper led to an immediate response by Robock [24] which was followed up in short order by a reply from Reisner [25]. I will not comment on that exchange, save to say that both critiques raised valid points.
2021 saw the publication of two independent papers that shed some light on the debate between the nuclear winter proponents and deniers. Tarshish and Romps [26] published results indicating the importance of latent heat (released when water vapor condenses) in facilitating the rise of fire plumes, pointing out that since Reisner et al. had assumed a US Standard Atmosphere such latent heat is not available, since the Standard Atmosphere is devoid of water content. As Robock et al. had assumed a typical atmospheric moisture content, their results indicated more soot being injected into the stratosphere. Hess [27] reported on a detailed comparison he did on the papers and author comments. His conclusion was that the difference between the outcomes was primarily to differences in the treatment of bc, pointing to the need to improve the models.
In 2021, Congress funded the Department of Energy to fund study of the atmospheric effects of a nuclear war. Preliminary results of that study, performed by the National Academy of Sciences, were released in late June 2025 and published some weeks later [28]. It would be impossible to explain its 25 each, findings and recommendations in a lesser number of pages, so I have condensed the key findings as follows, indicating the report's topical areas:
Overarching considerations: “Relevant U.S. agencies should coordinate the development of and support for a suite of model intercomparison projects (MIPs) to organize and assess models to reduce uncertainties in projections of the climatic and environment effects of nuclear war. . . .”
Employment scenarios and weapons effects: NNSA should coordinate among agencies and independent researchers to develop models of fuel composition and loading to facilitate better fire and fire spread modeling;
Plume rise, fate and transport of aerosols, and gas phase chemistry: The Earth system modeling community should develop rules of thumb estimates on plausible ranges of aerosol properties, and study how aerosols affect chemical and macroscopic behavior of the atmosphere;
Ecosystem impacts: Researchers should develop models to characterize key ecosystem responses to abrupt changes in conditions such as reduced temperature and incident sunlight, increased acidity and UV radiation, including differential response across regions;
Societal and economic impacts: “Agencies such as the U.S. Departments of Health and Human Services, Defense, Energy, and Agriculture should collaborate in the development and implementation of an enterprise-wide approach to assess the potential societal and economic impacts of a nuclear detonation on food, water, and health, taking into account disruption to global trade, financial markets, supply chains, and communication networks.” Also, agencies across the government “. . . should advance predictive modeling research to bolster preparedness strategies during the interdisaster period. . . . These efforts can help policymakers reach informed decisions, develop contingency plans, and design strategies to mitigate the worst outcomes and ensure food resilience in the face of such events.” Participation in a range of model intercomparison projects, to include even “global partners” was also recommended.
In my next post, I will briefly comment on the prospects for further progress in assessing the risk of a nuclear winter, and for developing the international consensus necessary for it to impact nuclear war planning and disarmament negotiations.
I promised that I would constantly remind my readership of the need for everyone who believes in freedom and democracy to behave in accordance with those beliefs, every day. To remind ourselves of what that means, see
Notes
[1] https://stephenschiff.substack.com/p/lets-do-away-with-nuclear-weapons
[2] https://stephenschiff.substack.com/p/mutually-assured-destruction-or-suicide
[3] https://stephenschiff.substack.com/p/nuclear-winter-update-part-1
[4] Robock, A. Volcanic eruptions and climate, Reviews of Geophysics, 38, 2 / May 2000, pp 191-219 https://agupubs.onlinelibrary.wiley.com/doi/10.1029/1998RG000054
[5] Manins, P.C., Cloud heights and stratospheric injections resulting from a thermonuclear war, Atmospheric Environment, 1967. Republished at https://doi.org/10.1016/0004-6981(85)90254-9
[6] NRC, Long-term worldwide effects of multiple nuclear weapons detonations, 1975. https://nap.nationalacademies.org/20139
[7] Glasstone, S. and P.J. Dolan, The effects of nuclear weapons, 3rd Edition, 1977, p299. A free pdf version can be obtained from https://www.osti.gov/biblio/6852629 I refer to the firestorm events as experiments, for that is what they were. In the first three cases, the perpetrators were attempting to determine whether they could utterly destroy their targets using incendiary bombs instead of the usual high explosives. Hiroshima is termed an experiment only because it was the first instance of nuclear weapon use against a civilian target. There, the firestorm was incidental.
[8] Lewis, K.N., The prompt and delayed effects of nuclear war, Scientific American 241(1), July 1977, pp 35-47
[9] Crutzen, P.J. And J.W. Birks, The atmosphere after a nuclear war: Twilight at noon, Ambio 11 (2/3), 1982, pp 114-125 Republished 2025 https://doi.org/10.1007/978-3-319-27460-7_5
[10] Turco, R.P., O.B. Toon, T.P. Ackerman, J.B. Pollack, Carl Sagan, Nuclear winter: Global consequences of multiple nuclear explosions, Science, 23 December 1983, pp 1283-1290 https://www.science.org/doi/10.1126/science.222.4630.1283
[12] NRC, The effects on the atmosphere of a major nuclear exchange, 1985 https://doi.org/10.17226/540
[13] Weinberger, Caspar W., The potential effects of nuclear war on the climate, 1985 https://nsarchive.gwu.edu/sites/default/files/documents/rcrn6j-upkqk/Doc-12.pdf
[14] https://stephenschiff.substack.com/p/nuclear-winter-update-part-1
[15] Haberle, R.M., T.P. Ackerman, O.B. Toon and J.L. Hollingsworth, Global transport of atmospheric smoke following a major nuclear exchange, Geophys. Res. Lett. 12, 405-408, 1985 https://doi.org/10.1029/GL012i006p00405
[16] Fromm, M., et al., Observations of boreal forest fire smoke in the stratosphere by POAM Ill, SAGE II, and lidar in 1998, Geophys. Res. Lett. 27, 1407-1410, 2000 https://doi.org/10.1029/GL0112000
[17] Fromm, M., and R. Servranckx, Transport of forest fire smoke above the tropopause by supercell convection, Geophys. Res. Lett. 30, 49_1-4, 2003 https://doi.org/10.1029/2002GL016820
[18] Fromm, M., et al., Pyro-cumulonimbus injection of smoke to the stratosphere: Observations and impact of a super blowup in northwestern Canada on 3–4 August 1998, J. Geophys. Res. 110, D0205_1-16, 2005 https://doi.org/10.1029/2004JD005350
[19] Robock, A., et al., Climatic consequences of regional nuclear conflicts, Atmos. Chem. Phys., 7, 2003–2012, 2007 www.atmos-chem-phys.net/7/2003/2007/
[20] Toon, O.B., et al., Atmospheric effects and societal consequences of regional scale nuclear conflicts and acts of individual nuclear terrorism, Atmos. Chem. Phys., 7, 1973–2002, 2007 www.atmos-chem-phys.net/7/1973/2007/
[21] Toon, O.B., et al., Consequences of Regional-Scale Nuclear Conflicts, Science, 315, 1224-1225, 2 March 2007 https://doi.org/10.1126/science.1137747
[22] Reisner, J., et al., Climate impact of a regional nuclear weapons exchange: An improved assessment based on detailed source calculations, JGR Atmospheres, 123, 2752-2772, 2018 https://doi.org/10.1002/2017/DJ027331
[23] https://frames.gov/catalog/57519 ; https://frames.gov/catalog/14623
[24] Robock, A., O.B. Toon and C.G. Bardeen, Comment on ”Climate impact of a regional nuclear weapons exchange: An improved assessment based on detailed source calculations” by J. Reisner, et al., JGR Atmospheres, 124, 2019 https://doi.org/10.1029/2019JD030777
[25] Reisner, J., et al., Reply to Comment by Robock et al. on “Climate Impact of a Regional Nuclear Weapon Exchange: An Improved Assessment Based on Detailed Source Calculations”, JGR Atmospheres, 124, 2019 https://doi.org/10.1029/2019JD031281
[26] Tarshish, N. and D.M. Romps, Latent Heating Is Required for Firestorm Plumes to Reach the Stratosphere, JGR Atmospheres, 127, 2021 https://doi. org/10.1029/2022JD036667
[27] Hess, G.D., The Impact of a Regional Nuclear Conflict between India and Pakistan: Two Views, J. Peace and Nuclear Disarmament 4, 163-175, 2021 https://doi.org/10.1080/25751654.2021.1882772
[28] National Academies of Science, 2025, Potential Environmental Effects of Nuclear War (2025) http://nap.nationalacademies.org/27515