Nuclear winter

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 or supervolcano eruption.

Mechanism

The nuclear winter scenario predicts that the huge fires caused by nuclear explosions (particularly from burning urban areas) would disperse large quantities of aerosol particles into the stratosphere, where they could remain for months or years, and which would significantly reduce the amount of sunlight that reached the surface. 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.

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.

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 C. 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, smooth Earth.

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 world's 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 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.

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 modern 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.

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.

Scientific Debate

The TTAPS study was widely reported and criticized in the media. Criticisms have not been supported by alternative model runs [1] [2]. Recent studies (2006) substantiate that smoke from urban firestorms in a regional war would lead to long lasting global cooling but in a less dramatic manner than the nuclear winter scenario, while a 2007 study of the effects of global nuclear war supported the conclusion that it would lead to full-scale nuclear winter.

Consequences of a regional nuclear war

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 produce as many direct fatalities as all of World War II and 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 (ca. 15 kiloton each) on major populated centres, the researchers estimated fatalities from 2.6 million to 16.7 million per country. Also, 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 could be "catastrophic" according to the researchers.

Ozone depletion

A 2008 study published in the Proceedings of the National Academy of Science 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 wreaking environmental havoc for at least a decade. 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 into the stratosphere. The soot would absorb enough solar radiation to heat surrounding gases, setting in motion a series chemical reactions that would break down the stratospheric ozone layer protecting Earth from harmful ultraviolet radiation.

Column ozone losses could exceed 20% globally, 25-45% at mid-latitudes, and 50-70% at northern high latitudes persisting for 5 years, with substantial losses continuing for 5 additional years. Column ozone amounts would remain near or below 220 Dobson units at all latitudes even after three years, constituting an extra-tropical “ozone hole”. Human health ailments like cataracts and skin cancer, as well as damage to plants, animals and ecosystems at mid-latitudes would likely rise sharply as ozone levels decreased and allowed more harmful UV light to reach Earth, according to the PNAS study. This study demonstrates that a small-scale, regional nuclear conflict is capable of triggering ozone losses even larger than losses that predicted in the 1980s following a full-scale nuclear war. The missing piece back then was that the models at the time could not account for the rise of the smoke plume and consequent heating of the stratosphere.

2007 study on global nuclear war

A study published in the Journal of Geophysical Research in July 2007, Nuclear winter revisited with a modern climate model and current nuclear arsenals: Still catastrophic consequences, 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 described as being only about a third 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 (1 Tg is equal to 10¹² grams), 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 1/3 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."

Kuwait wells in the first 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.

Cornell Professor Carl Sagan of the TTAPS study warned in January of 1991 that so much smoke from the fires "might get so high as to disrupt agriculture in much of South Asia...." Sagan later conceded in his book The Demon-Haunted World that this prediction 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."

The 2007 study discussed above 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 or the burning of cities that would be expected to follow a nuclear strike, would loft significant amounts of smoke into the stratosphere:

Stenchikov et al. [2006b] conducted detailed, high-resolution smoke plume simulations with the RAMS regional climate model [e.g., Miguez-Macho et al., 2005] 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].

References

• Budyko, M. I., G. S. Golitsyn, Y. A. Izrael Global Climatic Catastrophes Springer, 99 pages, September 1988, ISBN 0-387-18647-6
• 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, C. Sagan, Nuclear Winter: Global Consequences of Multiple Nuclear Explosions, Science, V. 222, No; 4630, December 23, 1983.
• Mark A. Harwell Nuclear Winter: The Human and Environmental Consequences of Nuclear War Springer, 179 pages , November 1984, ISBN 0-387-96093-7
• Mills, Michael J., Owen B. Toon, Richard P. Turco, Douglas E. Kinnison, Rolando R. Garcia, 2008, "Massive global ozone loss predicted following regional nuclear conflict," PNAS, doi:10.1073/pnas.0710058105.
• 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
• Guide to Nuclear Winter Study Papers, 1972-1993. Lawrence Livermore Laboratory
• Robock, Alan, Luke Oman, Georgiy L. Stenchikov, Owen B. Toon, Charles Bardeen, and Richard P. Turco, 2007a: Climatic consequences of regional nuclear conflicts. Atm. Chem. Phys., 7, 2003-2012.
• Robock, Alan, Luke Oman, and Georgiy L. Stenchikov, 2007b: Nuclear winter revisited with a modern climate model and current nuclear arsenals: Still catastrophic consequences. J. Geophys. Res., 112, D13107, doi:10.1029/2006JD008235.
• Toon, Owen B., Richard P. Turco, Alan Robock, Charles Bardeen, Luke Oman, and Georgiy L. Stenchikov, 2007a: Atmospheric effects and societal consequences of regional scale nuclear conflicts and acts of individual nuclear terrorism. Atm. Chem. Phys., 7, 1973-2002.
• Toon, Owen B., Alan Robock, Richard P. Turco, Charles Bardeen, Luke Oman, and Georgiy L. Stenchikov, 2007b: Consequences of regional-scale nuclear conflicts. Science, 315, 1224-1225.
• 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.

See also

• Nuclear weapon
• Doomsday device
• Nuclear summer
• Volcanic winter

External links

• Global Atmospheric Consequences of Nuclear War, the 1983 study conducted by TTAPS.
• Nuclear Winter Simulation Animation
• New studies of climatic consequences of regional nuclear conflict from Alan Robock, including links to new studies published in 2007.