Nuclear winter
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Nuclear winter is a hypothetical global climate condition that is predicted to be a possible outcome of a large-scale nuclear war. It is thought that severely cold weather can be caused by detonating large numbers of nuclear weapons, especially over flammable targets such as cities, where large amounts of smoke and soot would be injected into the Earth's stratosphere. The term has also been applied to one of the after-effects of an asteroid impact.
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[edit] Supposed Mechanism
Large quantities of aerosol particles dispersed into the atmosphere would significantly reduce the amount of sunlight that reached the surface, and could potentially remain in the stratosphere for months or even years. The ash and dust would be carried by the midlatitude west-to-east winds, forming a uniform belt of particles encircling the northern hemisphere from 30° to 60° latitude (as the main targets of most nuclear war scenarios are located almost exclusively in these latitudes). The dust clouds would then block out much of the sun's light, causing surface temperatures to drop drastically.
[edit] History
In 1982 a special issue of the journal Ambio was devoted to the possible environmental consequences of nuclear war; it included an article by Paul Crutzen and J. Birks on atmospheric effects. They re-assessed and re-affirmed the consequences for the ozone layer noted in the 1975 National Academies of Science report (up to 70% of the ozone layer might be destroyed); and drew attention for the first time to the likelihood that large amounts of smoke and dust would be created.
[edit] TTAPS (1983)
In 1983 the "TTAPS" study (from the initials of the last names of its authors, R.P. Turco, O.B. Toon, T.P. Ackerman, J.B. Pollack, and Carl Sagan) undertook a systematic study of the atmospheric consequences; partly inspired to write the paper both by the suggestions of one Dr. A.M. Salzberg (who, unlike the TTAPS authors, believed that the initial dust thrown into the air would be primarily responsible for the climate changes) and by cooling effects due to dust storms on Mars. To carry out a calculation of the effect they used a very simplified two dimensional model of the Earth's atmosphere that assumed that conditions at a given latitude were constant. The model also assumed a solid, flat earth.
[edit] WCRP report (1986)
In 1984 the WMO commissioned G. S. Golitsyn and N. A. Phillips to review the state of the science. They found that studies generally assumed a scenario that half of the worlds nuclear weapons would be used, ~5000 Mt, destroying approximately 1,000 cities, and creating large quantities of carbonaceous smoke - 1–2 × 1014 grams being mostly likely, with a range of 0.2 – 6.4 × 1014 grams (NAS; TTAPS assumed 2.25 × 1014). The smoke resulting would be largely opaque to solar radiation but transparent to infra-red, thus cooling by blocking sunlight but not causing warming from enhancing the greenhouse effect. The optical depth of the smoke can be much greater than unity. Forest fires resulting from non-urban targets could increase aersol production further. Dust from near-surface explosions against hardened targets also contributes; each Mt-equivalent of explosion could release up to 5 Mt of dust, but most would quickly fall out; high altitude dust is estimated at 0.1-1 Mt per Mt-equivalent of explosion. Burning of crude oil could also contribute substantially.
The 1-D radiative-convective models used in these studies produced a range of results, with coolings up to 15-42 °C between 14 and 35 days after the war, with a "baseline" of about 20 °C. Somewhat more sophisticated calculations using 3-D GCMs (Alexandrov and Stenchikov (1983); Covey, Schneider and Thompson (1984); which would be considered primitive by today standards) produced similar results: temperature drops of between 20 and 40 °C, though with regional variations.
All calculations show large heating (up to 80 °C) at the top of the smoke layer at about 10 km; this implies a substantial modification of the circulation there and the possibility of advection of the cloud into low latitudes and the southern hemisphere.
The report made no attempt to compare the likely human impacts of the post-war cooling to the direct deaths from explosions.
[edit] TTAPS (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:
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 of 3° to 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 drops of 2° to 6° C. Ozone depletion of 50% leading to 200% increase in UV radiation incident on surface.
[edit] Scientific Debate
Although the TTAPS study was widely quoted in the media, criticisms have not been supported by alternative model runs[1] [1].
[edit] Kuwait wells in the Gulf War
The burning of 526 Kuwaiti oil wells during the Persian Gulf War showed the effects of vast emissions of particulate matter into the atmosphere in a geographically limited area; directly underneath the smoke plume constrained model calculations suggested that daytime temperature may have dropped by ~10°C within ~200 km of the source. [2]
Cornell Professor Carl Sagan, of the TTAPS study, predicted on ABC's Nightline that the smoky oil fires could cause a worldwide ecological disaster of black clouds resulting in global cooling. Retired atmospheric physicist and climate change skeptic Fred Singer dismissed Sagan's prediction as nonsense, predicting that the smoke would dissipate in a matter of days. In his book The Demon-Haunted World, Sagan gave a list of errors he had made (including his predictions about the effects of the Kuwaiti oil fires) as an example of how science is a learning process.
[edit] References
- Paul J. Crutzen and John W. Birks, The Atmosphere After a Nuclear War: Twilight at Noon, Ambio, Vol 11, No 2-3, p 114, 1982.
- Golitsyn, G.S. and Phillips, N.A. WCRP, Possible climatic consequences of a major nuclear war, WCP-113, WMO/TD #99, 1986.
- R.P. Turco, O.B. Toon, T.P. Ackerman, J.B. Pollack, Carl Sagan, Nuclear Winter: Global Consequences of Multiple Nuclear Explosions, Science, V. 222, No; 4630, December 23, 1983.
- 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.
- Mark A. Harwell Nuclear Winter: The Human and Environmental Consequences of Nuclear War Springer, 179 pages , November 1984, ISBN 0-387-96093-7
- N. N. Moiseev Man, nature and the future of civilization: "nuclear winter" and the problem of a "permissible threshold" Novosti Press Agency Pub. House, Moscow, 92 pages, January 1986, ASIN: B0007B9FHG
- M. I. Budyko, G. S. Golitsyn, Y. A. Izrael Global Climatic Catastrophes Springer, 99 pages, September 1988, ISBN 0-387-18647-6
- Guide to Nuclear Winter Study Papers, 1972-1993. Lawrence Livermore Laboratory
