August 19, 2023: Nuclear Winter
Good evening. Today we will have a cheerful topic: the prospects for nuclear winter in the aftermath of a nuclear war. A nuclear winter is a hypothesized scenario whereby, as a result of firestorms resulting from a nuclear war, large amounts of soot enter the atmosphere, block sunlight, inhibit photosynthesis, and threaten human civilization and life itself. The specter of nuclear winter loomed large in 1980s disarmament politics, and today it has made a comeback. And so we will examine how plausible this notion is.
The term “nuclear winter” was coined in a 1983 paper by Richard Turco, Owen Toon, Thomas Ackerman, James Pollack, and Carl Sagan, also known as the TTAPS paper after the authors’ initials. The paper presents a simple model of how a nuclear winter may came about, and it was written with the explicit intention of making a case for arms control.
While the term “nuclear winter” was new in 1983, the concept was not. The first study of the phenemonon, according to this source, was conducted shortly before Ivy Mike, the first test of a thermonuclear (hydrogen) bomb in 1952. The study found no risk of nuclear winter. A study by the U. S. Weather Bureau (now the National Weather Service) in 1956 and this 1966 study from the RAND Corporation assessed that there was a risk that a nuclear exchange could trigger an ice age. This 1975 report from the National Research Council envisioned less of a risk.
A year following TTAPS, Paul Ehrlich and coauthors (yes, that Paul Ehrlich) wrote The Cold and the Dark, painting a grim picture of a post-nuclear war world. There was relatively little activity on the nuclear winter question immediately after the end of the Cold War. In 2007, this study found that 100 15-kiloton detonations (the size of the bomb dropped on Hiroshima) would be enough to trigger a nuclear winter. Another 2007 study added to the fears by assessing that nuclear winter could also disrupt the hydrological cycle, leading to less rain, a further hit to plant growth, and greater disruption to the food chain. A 2014 study, again modeling the detonation of 100 15-kt weapons, found that it would trigger nuclear winter as well as destroy 20-50% of the stratospheric ozone layer.
A 2019 study found that the detonation of all nuclear weapons permitted to the United States and Russia under New START would be enough to trigger a nuclear winter. A pair of studies in 2022 found that a nuclear winter would have catastrophic effects for food production and for biodiversity. It has been proposed that countries agree to a maximum of 100 warheads, if this is the threshold to trigger a nuclear winter.
The term “nuclear” winter is a misnomer since the proximate cause is soot in the atmosphere, and nuclear detonations need not be the mechanism by which the soot is produced. The TTAPS paper came shortly after, and was inspired by, the Alvarez Hypothesis that an asteroid impact created a large amount of atmospheric dust and caused the K-T extinction, including that of nonavian dinosaurs. The firestorms to create soot could be caused by conventional weapons. In World War II, the five largest fires occurred at Hamburg, Dresden, Tokyo, Hiroshima, and Nagasaki, with only two caused by nuclear weapons, and all occurred in 1945 except for Hamburg, which was in 1943. No global climactic effect was found from these fires, though with the technology of the day, none should have been detected under the model of Toon et al. Analogous effects should also be observed from wildfires and volcanic eruptions. The latter is known as a volcanic winter and has been observed, such as in 1816, the “Year Without a Summer” resulting from the eruption of Mt. Tambora in Indonesia.
Deriving from the model in the TTAPS paper, the uncontrolled combustion of large quantities of crude oil should also trigger a nuclear winter. This hypothesis was put to the test in 1991, when the retreating Iraqi army set fire to oil fields in Kuwait. Far less soot was lofted into the atmosphere than was predicted by the TTAPS model, and no global climactic effects were observed.
There has been much criticism of the nuclear winter hypothesis, but I am aware of only one peer-reviewed study, this one by Jon Reisner et al. The study finds that in the kind of nuclear exchange modeled by Toon et al., a similar amount (~5 million tons) of soot would be produced, but only a small portion would reach the upper atmosphere where it would have an impact on weather. And for a given amount, the impact would be less than modeled by Toon et al. Reisner et al. conclude that significant global cooling from a limited exchange of weapons would be highly unlikely.
In the 1980s, Russell Seitz argued that the TTAPS paper makes worst-case assumptions at every point in their model. While a worst case assumption might be plausible once, when many such assumptions are chained together, the result is implausible.
Even at the time of the TTAPS paper, there had been a trend toward miniaturization, or smaller-yield, better targeted nuclear weapons, which would have led them to overestimate the total yield in any exchange.
It is not just the TTAPS paper, but most models of nuclear winter explicitly make a case for disarmament. A political agenda behind a paper is not problematic in and of itself—why would science be done if there was no political motivation—but one must always be alert to how politics might cloud the conclusions. The analyst Leon Gouré documented how the Soviet Union promoted the idea of nuclear winter for propaganda purposes, with the intention of influencing peace groups. The Russian spy-turned-defector Sergei Tretyakov went further, alleging (without proof) that the Soviets fabricated the concept of nuclear winter to stop NATO deployment of Pershing II missiles in Europe, and also that they financed Ambio, a journal that published some early work on nuclear winter, as well as peace groups.
All in all, I find the case for nuclear winter to be much shakier than many disarmament advocates imagine. The Future of Life Institute, for instance, discusses nuclear winter with little hint that the concept is contested, and insofar as they acknowledge uncertainty, it is to invoke the precautionary principle. Though dated, this paper gives a good overview of some of the issues involved, and even before the Kuwait oil fires, it highlights some flaws with nuclear winter modeling.
One (of several) things I would like to know is what wildfires can tell us about nuclear winter risks. Russell Seitz in 1986 discussed wildfires in Siberia and how they failed to confirm the TTAPS model. In 2019, Toon et al. discussed wildfires in Canada and how they confirm their model of nuclear winter. I am not aware of a systematic treatment of the subject.
The relationship between the nuclear freeze movement and the environmental movement of the 1980s is fertile ground for exploration. Spencer Weart has done that, and Matthias Dörries has documented how the TTAPS paper helped pave the way for popularization of anthropogenic climate change as an issue; while the two are related only tangentially, both reflect concerns of artificial activities on the atmosphere. Carl Sagan and Paul Ehrlich are among the figures that were prominent in both movements. Both movements are characterized by opposition to both nuclear weapons and nuclear energy, with the German Green Party linking and opposing both forms of nuclear technology. Another connection is that Richard Turco, lead author of the TTAPS paper, was the doctoral advisor to Mark Jacobson, who himself has conducted questionable modeling of the world energy system.
It is not disputed that a nuclear war would be a catastrophic event, whether or not nuclear winter has any validity. Taking a consequentialist approach, many authors of the papers cited above immodestly take credit for saving the world with their idea. And maybe this argument is sound. But it really has to be asked, is the case for disarmament really that strong if advocates feel the need to invoke sketchy science?
Quick Hits
A couple months ago, Will Freeman from the Council on Foreign Relations wrote a profile on organized crime in Ecuador. The situation is so bad as to pose an existential risk to the country.
Randal O’Toole wrote a piece, reiterating themes he has covered many times, arguing that surveys find that the public has a preference for single family homes, at least in greater proportion than they are being built, and that high density areas are inherently more expensive. I don’t see how these two points can coexist, as markets are much more informative than surveys about public preferences.
Theresa Hitchens of Breaking Defense discusses progress in directed energy weapons and that the Missile Defense Agency is increasing usage of these weapons for purposes beyond just research. I have commented on directed energy weapons several times, including last year.