'''Nuclear winter''' is a hypothetical global [[climate]] condition that is predicted to be a possible outcome of a large-scale [[Nuclear warfare|nuclear war]]. It is thought that severely cold weather can be caused by detonating large numbers of [[nuclear weapons]], especially over [[fire|flammable]] targets such as [[city|cities]], where large amounts of [[smoke]] and [[soot]] would be injected into the [[Earth]]'s [[stratosphere]]. 

This layer of particles would significantly reduce the amount of [[sunlight]] that reached the surface, and could potentially remain in the stratosphere for weeks or even years (smoke and soot arising from the burning [[petroleum]] fuels and [[plastic]]s would absorb sunlight much more effectively than would smoke from burning [[wood]]). The ash 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]]. These thick black clouds could block out much of the sun's light for a period as long as several weeks, causing surface temperatures to drop by as much as 30°C during the [[occlusion]]. 

The combination of darkness and killing [[frost]]s, combined with high doses of [[ionizing radiation|radiation]] from [[nuclear fallout]], would severely damage [[plant]] life in the region. The extreme cold, high radiation levels, and the widespread destruction of industrial, medical, and transportation infrastructures along with food supplies and crops would trigger a massive death toll from starvation, exposure, and disease. It was also thought that [[nitrogen oxide]]s generated by the blasts would degrade the [[ozone layer]], as had been observed in the first [[fusion bomb|thermonuclear]] blasts. Secondary effects from ozone depletion (and concomitant increases in ultraviolet radiation) would be significant, with impacts on the viability of most human staple agricultural crops as well as disruption of ocean food chains by killing off [[phytoplankton]].

It is also said that a large enough [[impact event]] with the Earth or a [[supervolcano]] eruption will produce exactly the same problems and effects as a Nuclear Winter would and that these scenarios will be called Nuclear Winter as a result.
  
== History ==  
  
In 1982 a special issue of the journal [[Ambio]] was devoted to the possible environmenal 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 likely large amounts of smoke that would be released. 
 
=== 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 simplified two dimensional model of the Earth's atmosphere that assumed that conditions at a given latitude were constant.

=== [[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, about 5-6,000 Mt, destroying approximately 1,000 cities, and creating large quantities of black carbonaceous smoke - 1–2&nbsp;×&nbsp;10<sup>14</sup>&nbsp;grams being mostly likely, with a range of 0.2&nbsp;–&nbsp;6.4&nbsp;×&nbsp;10<sup>14<sup> (NAS; TTAPS assumed 2.25&nbsp;×&nbsp;10<sup>14</sup>). The smoke resulting would be largely opaque to solar radiation but transparent to infra-red, thus cooling by blocking sunshine but not causing warming from enhancing the [[greenhouse effect]]. The [[optical depth]] of the smoke would be four or more. Forest fires resulting from non-urban targets could enhance these numbers. Dust from near-surface explosions against hardened targets could also contribute; each Mt 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 of explosion. The theory of large-scale fires was recognised as a weak point; with data from Hamburg and Hiroshima cited as examples. 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 of 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. 

== Kuwait wells in the Gulf War == 
[[Kuwaiti oil fires|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; underneath the smoke plume constrained model calculations suggested that daytime temperature may have dropped by ~10°C within ~200 km of the source[http://www.nature.com/nature/journal/v351/n6325/abs/351363a0.html;jsessionid=C8A0C7E25D19554C81879A7C5420B60A]. However, the paper notes that "with the smoke failing to reach the stratosphere...close analogies with nuclear winter and large volcanic eruptions are inappropriate."

== 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.
* Mark A. Harwell "Nuclear Winter: The Human and Environmental Consequences of Nuclear War" Springer, 179 pages ,  November 1984
* [[Nikita Moiseyev|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

==See also==
*[[Doomsday device]] 
*[[Nuclear summer]] 
*[[Volcanic winter]]

==External links==  
* For a more detailed discussion of nuclear winter see [http://www.the-spa.com/jon.roland/vri/nwaos.htm Nuclear Winter and Other Scenarios].
* [http://www.atomicarchive.com/Movies/Movie6.shtml Nuclear Winter Simulation Animation]

[[Category:Nuclear weapons]][[Category:Climatology]][[Category:Climate forcing agents]]
[[Category:Environmental disasters]]

[[de:Nuklearer Winter]]
[[es:Invierno nuclear]]
[[fr:Hiver nucléaire]]
[[it:Inverno nucleare]]
[[he:חורף גרעיני]]
[[nl:Nucleaire winter]]
[[ja:核の冬]]
[[pl:Zima nuklearna]]
[[pt:Inverno Nuclear]]
[[ru:Ядерная зима]]
[[sk:Nukleárna zima]]
[[sv:Kärnvapenvinter]]
[[zh:核冬天]]