Stuart Parkinson looks into why the climatic disaster which would follow a potential nuclear war has been forgotten.

Article from SGR Newsletter 27, July 2003

Update

Since this article was written, many new research papers have been published on the subject of nuclear winter, including SGR's own article, Could one Trident submarine cause nuclear winter? For more details and analysis, see SGR's project page on the Nuclear Weapons Threat.

Original article

During the 1980s, one of the major concerns of the effects of a potential nuclear war was the possibility of it causing a 'nuclear winter' - a catastrophic change in climate caused by the ejection of massive amounts of dust and smoke into the atmosphere during the course of such a war. Yet, since the end of the Cold War in 1989, discussion of the potential for major climatic changes due to a nuclear conflict has virtually ceased - despite the fact the large arsenals of nuclear weapons still remain on alert status, and hence such a conflict could still happen by accident. And of course, recent tensions, in particular between India and Pakistan, could still lead to an intentional nuclear war.

The devastation of a nuclear winter

Obviously, when a nuclear bomb hits a target, it causes a massive amount of devastation, with the heat, blast and radiation killing tens or hundreds of thousands of people instantly and causing huge damage to infrastructure. But in addition to this, a nuclear explosion throws up massive amounts of dust and smoke. For example, a large nuclear bomb bursting at ground level would throw up about a million tonnes of dust.

As a consequence of a nuclear war, then, the dust and the smoke produced would block out a large fraction of the sunlight and the sun's heat from the earth's surface, so it would quickly become be dark and cold - temperatures would drop by something in the region of 10-20ºC - many places would feel like they were in an arctic winter. It would take months for the sunlight to get back to near normal. The drop in light and temperature would quickly kill crops and other plant and animal life while humans, already suffering from the direct effects of the war, would be vulnerable to malnutrition and disease on a massive scale.

In the case of an (e.g.) accidental nuclear exchange between the USA and Russia, the main effects would be felt in the northern hemisphere, as the dust and smoke would quickly circulate across this area. But even in this case, it would soon affect the tropics - where crops and other plant/ animal life are especially sensitive to cold. Hence, even in these areas there would be major problems.

While the temperature at the surface would be low, the temperature of the upper part of the troposphere (5-11 km) would rise because of sunlight absorbed by the smoke, so there would be a huge temperature inversion. That would keep many other pollutants produced by widespread fires (e.g. dioxins, PCBs, sulphurous gases) down at the levels people breathe, making a very dense and highly toxic smog.

One further environmental problem would be widespread destruction of the ozone layer caused by high levels of nitrogen oxides. The average loss of ozone could be as much as 70% - much higher than that currently cause by CFCs. So after several months when the smoke cleared and the sun began to shine again, there would be a large increase of UV radiation reaching the earth's surface. This would be bad for humans (e.g. eye and skin damage), but the major effect would be for other living things, notably sensitive plankton, which are at the bottom layer of the whole marine food chain. Animals would also suffer - blindness would be common - and blind animals would quickly starve.

Altogether, nuclear winter would be an ecological disaster of a similar magnitude to the major extinctions of the past, such as that at the end of the Cretaceous period 65 million years ago when 75% of all species died out, including the dinosaurs. An added factor after a nuclear war would be radioactive contamination giving worldwide background radiation doses many times larger than has ever happened during the 3 billion years of evolution.
 

The research on nuclear winter

The prediction of nuclear winter was first published by a group headed by Carl Sagan in 1983 (TTAPS, 1983). The research group became known as 'TTAPS', after the initials of the five scientists involved. A number of other studies were published in the next few years, including major reports by The Swedish Academy of Sciences, and SCOPE (Scientific Committee on Problems of the Environment), and the U.S. National Research Council (NRC, 1985).

Throughout this period, many attempts were made by government and military scientists to play down the possible consequences. They argued that the effects would not be nearly so severe, and began talking of a 'nuclear autumn'.

In 1990 the TTAPS group decided to publish a further paper (TTAPS, 1990), in which they reviewed in detail the later studies, and made some modifications to their 1983 results. Some of these were in the direction of more severe changes, others towards milder changes. But overall the general picture was little changed. One very notable conclusion that was reiterated from the 1983 study was that if oil refineries were the main targets, only 100 bombs would be enough to cause a nuclear winter.

Sagan and Turco (one of the 'T's) followed up their second paper by publishing a book: "The Path Where No Man Thought". This gives an account of current conclusions for the serious non-specialist reader. It gives detailed descriptions of nuclear winters of different severity according to how many weapons were used, and against what targets.

Recent history

Since 1990, as far as we can ascertain, no new research has been carried out into the possible climatic effects of a nuclear conflict. Yet since 1990, major improvements to climate system models have occurred in the international scientific effort to understand human-induced Climate Change. Meanwhile, even though the threat of a large-scale nuclear conflict between the USA and Russia has diminished, the threat of a smaller scale nuclear conflict has perhaps increased, for example due to increasing tensions between India and Pakistan over Kashmir.

So now seems an especially appropriate time to do further research on the climatic effects of a nuclear war. But worryingly no one is doing it. Steven Starr and Dr Neil Arya of the Canadian organisation, Physicians for Global Survival, have been trying to encourage former members of the TTAPS team to update their work, as well other scientists in the area. SGR has also contacted climate modellers in the UK to see if we can find anyone who might be interested. So far neither PGS nor SGR have had any luck. Is this subject just too controversial for climate scientists to risk getting involved in? Will no one stick their neck out for such an important piece of work?

With thanks to Steven Starr for assistance with this article.

References

Sagan C., Turco R.P. (1990). A Path Where No Man Thought. Random House.
Turco, R.P., Toon, A.B., Ackerman, T.P., Pollack, J.B., Sagan, C. (TTAPS) (1983). Global Atmoshperic Consequences of Nuclear War. Science, vol.222, March.
Turco, R.P., Toon, A.B., Ackerman, T.P., Pollack, J.B., Sagan, C. (TTAPS) (1990). Climate and Smoke: An Appraisal of Nuclear Winter. Science, volume 247, pp.167-168, January.
U.S. National Research Council (1985). The Effects on the Atmosphere of a Major Nuclear Exchange.