Editing Nuclear winter (section)

== Mechanism ==
{{Main|Pyrocumulonimbus cloud}}
[[File:Picture of a pyro-cumulonimbus taken from a commercial airliner.jpg|thumb|Picture of a [[pyrocumulonimbus cloud]] taken from a commercial airliner cruising at about 10 km. In 2002, various sensing instruments detected 17 distinct pyrocumulonimbus cloud events in [[North America]] alone.<ref name="Fire-Breathing Storm Systems" />]]
The nuclear winter scenario assumes that 100 or more city firestorms<ref name=pnas.0710058105>{{cite journal |title=Massive global ozone loss predicted following regional nuclear conflict |last1=Mills |first1=Michael J. |last2=Toon|first2=Owen B. |last3=Turco|first3=Richard P. |last4=Kinnison |first4=Douglas E. |last5=Garcia|first5=Rolando R. |date=April 8, 2008 |journal=PNAS |volume=105 |issue=14 |pages=5307–5312 |doi=10.1073/pnas.0710058105|pmid=18391218 |pmc=2291128 |bibcode=2008PNAS..105.5307M |doi-access=free }} "50 Hiroshima-size (15 kt) bombs could generate 1–5 Tg of black carbon aerosol particles in the upper troposphere, after an initial 20% removal in "black rains" induced by firestorms..." & "the 1 to 5 Tg soot source term derives from a thorough study of the smoke produced by firestorms..."</ref><ref name="climate.envsci.rutgers.edu">{{harvnb|Toon|Turco|Robock|Bardeen|2007|p=1994}}. "the injection height of the smoke is controlled by the energy release from the burning fuel not from the nuclear explosion".</ref> are ignited by [[nuclear explosion]]s,<ref name="Robock Toon 2012"/> and that the firestorms lift large amounts of sooty smoke into the upper [[troposphere]] and lower stratosphere by the movement offered by the pyrocumulonimbus clouds that form during a firestorm. At {{convert|10|-|15|km|mi|abbr=off|0}} above the Earth's surface, the absorption of sunlight could further heat the soot in the smoke, lifting some or all of it into the [[stratosphere]], where the smoke could persist for years if there is no rain to wash it out. This aerosol of particles could heat the stratosphere and prevent a portion of the sun's light from reaching the surface, causing surface temperatures to drop drastically. In this scenario it is predicted{{By whom|date=July 2017}} that surface air temperatures would be the same as, or colder than, a given region's winter for months to years on end.

The modeled stable [[inversion (meteorology)|inversion layer]] of hot soot between the troposphere and high stratosphere that produces the anti-greenhouse effect was dubbed the "Smokeosphere" by [[Stephen Schneider (scientist)|Stephen Schneider]] et al. in their 1988 paper.<ref name=autogenerated4/>{{Sfn | Badash |2009 | p = 184}}<ref name="assets.cambridge.org">{{Cite book |last1=Cotton |first1=William R. |url=http://assets.cambridge.org/97805218/40866/frontmatter/9780521840866_frontmatter.pdf |title=Human Impacts on Weather and Climate |last2=Pielke |first2=Roger A. |date=February 2007 |publisher=Cambridge University Press |isbn=978-0-521-84086-6 |edition=2nd |language=en |access-date=2014-09-22 |archive-url=https://web.archive.org/web/20140924042009/http://assets.cambridge.org/97805218/40866/frontmatter/9780521840866_frontmatter.pdf |archive-date=2014-09-24 |url-status=live}}</ref>

Although it is common in the climate models to consider city firestorms, these need not be ignited by nuclear devices;{{Sfn | Badash |2009 | pp = 242–244}} more conventional ignition sources can instead be the spark of the firestorms. Prior to the previously mentioned solar heating effect, the soot's injection height is controlled by the [[power (physics)|rate of energy release]] from the firestorm's fuel, not the size of an initial nuclear explosion.<ref name="climate.envsci.rutgers.edu" /> For example, the [[mushroom cloud]] from the [[Little Boy|bomb dropped on Hiroshima]] reached a height of six kilometers (middle troposphere) within a few minutes and then dissipated due to winds, while the individual fires within the city took almost three hours to form into a firestorm and produce a [[pyrocumulus]] cloud, a cloud that is assumed to have reached upper tropospheric heights, as over its multiple hours of burning, the firestorm released an estimated 1000 times the energy of the bomb.{{sfn|Toon|Turco|Robock|Bardeen|2007|p=1994 |loc="Altitudes of smoke columns"}}

As the incendiary effects of a [[nuclear explosion]] do not present any especially characteristic features,<ref name="The Effects of Nuclear Weapons">{{Citation |editor-last=Glasstone |editor-first=Samuel |editor2-last=Dolan |editor2-first=Philip J. |year=1977 |chapter="Chapter VII – Thermal Radiation and Its Effects |title=The Effects of Nuclear Weapons |edition=Third |publisher=United States Department of Defense and the Energy Research and Development Administration |url=http://www.fourmilab.ch/etexts/www/effects/ |chapter-url=http://www.fourmilab.ch/etexts/www/effects/eonw_7.pdf#zoom=100 |access-date=2014-09-22 |archive-url=https://web.archive.org/web/20141031024929/http://www.fourmilab.ch/etexts/www/effects/ |archive-date=2014-10-31  |pages=300, § "Mass Fires" ¶ 7.61}}</ref> it is estimated by those with [[strategic bombing]] experience that as the city was a firestorm hazard, the same fire ferocity and building damage produced at Hiroshima by one [[Little Boy|16-kiloton nuclear bomb]] from a single [[Boeing B-29 Superfortress|B-29 bomber]] could have been produced instead by the conventional use of about 1.2 [[kilotons]] of [[incendiary bomb]]s from 220 B-29s distributed over the city.<ref name="The Effects of Nuclear Weapons"/><ref name="here">{{cite book |editor-last=D'Olier |editor-first=Franklin |editor-link=Franklin D'Olier |year=1946 |title=United States Strategic Bombing Survey, Summary Report (Pacific War) |location=Washington |publisher=United States Government Printing Office |url=http://www.anesi.com/ussbs01.htm |access-date=November 6, 2013 |url-status=live |archive-url=https://web.archive.org/web/20080516014539/http://www.anesi.com/ussbs01.htm |archive-date=May 16, 2008}}</ref><ref>{{cite web| url=http://marshall.csu.edu.au/Marshalls/html/WWII/USSBS_Summary.html |title=United States Strategic Bombing Survey, Summary Report|quotation=+would have required 220 B-29s carrying 1,200 tons of incendiary bombs, 400 tons of high-explosive bombs, and 500 tons of anti-personnel fragmentation bombs, if conventional weapons, rather than an atomic bomb, had been used. One hundred and twenty-five B-29s carrying 1,200 tons of bombs (Page 25 ) would have been required to approximate the damage and casualties at Nagasaki. This estimate pre-supposed bombing under conditions similar to those existing when the atomic bombs were dropped and bombing accuracy equal to the average attained by the Twentieth Air Force during the last 3 months of the war|website=Marshall.csu.edu.au|date=October 9, 2005 |access-date=2016-05-11|archive-url= https://web.archive.org/web/20160314161528/http://marshall.csu.edu.au/Marshalls/html/WWII/USSBS_Summary.html |archive-date=2016-03-14|url-status=live}}</ref>

While the [[bombing of Dresden|firestorms of Dresden]] and Hiroshima and the [[Operation Meetinghouse|mass fires of Tokyo]] and [[bombing of Nagasaki|Nagasaki]] occurred within mere months in 1945, the more intense and [[bombing of Hamburg|conventionally lit Hamburg firestorm]] occurred in 1943. Despite the separation in time, ferocity and area burned, leading modelers of the hypothesis state that these five fires potentially placed five percent as much smoke into the stratosphere as the hypothetical 100 nuclear-ignited fires discussed in modern models.<ref name="ReferenceC"/> While it is believed that the modeled climate-cooling-effects from the mass of soot injected into the stratosphere by 100 firestorms (one to five million [[Tonne|metric tons]]) would have been detectable with technical instruments in WWII, five percent of that would not have been possible to observe at that time.<ref name="ReferenceC"/>

=== Aerosol removal timescale ===
[[File:SmokeCeilingInLochcarron.jpg|thumb|Smoke rising in [[Lochcarron]], [[Scotland]], is stopped by an overlying natural low-level inversion layer of warmer air (2006).]]
The exact timescale for how long this smoke remains, and thus how severely this smoke affects the climate once it reaches the stratosphere, is dependent on both chemical and physical removal processes.<ref name="babel.hathitrust.org" />

The most important physical removal mechanism is "[[Rainout (radioactivity)|rainout]]", both during the "fire-driven [[convection|convective]] column" phase, which produces "[[firestorm|black rain]]" near the fire site, and rainout after the [[Plume (hydrodynamics)|convective plume]]'s dispersal, where the smoke is no longer concentrated and thus "wet removal" is believed to be very efficient.{{sfn|Toon|Turco|Robock|Bardeen|2007|p=1994}} However, these efficient removal mechanisms in the troposphere are avoided in the [[Robock]] 2007 study, where solar heating is modeled to quickly loft the soot into the stratosphere, "detraining" or separating the darker soot particles from the fire clouds' whiter [[water condensation]].{{sfn|Toon|Turco|Robock|Bardeen|2007|pp=1994–1996}}

Once in the stratosphere, the [[Physics|physical]] removal mechanisms affecting the timescale of the soot particles' residence are how quickly the aerosol of soot collides and [[aerosol#coagulate|coagulates]] with other particles via [[Brownian motion]],<ref name="babel.hathitrust.org" />{{sfn|Toon|Turco|Robock|Bardeen|2007|pp=1997–1998}}<ref name="a.mpg.de">[http://www.atmosphere.mpg.de/enid/906c8d956939bb335e9b051e10f45223,0/2__Particles/-_Transformation_and_removal_296.html Transformation and removal] {{webarchive| url=https://web.archive.org/web/20110727031911/http://www.atmosphere.mpg.de/enid/906c8d956939bb335e9b051e10f45223,0/2__Particles/-_Transformation_and_removal_296.html |date=2011-07-27 }} J. Gourdeau, LaMP Clermont-Ferrand, France, March 12, 2003</ref> and falls out of the atmosphere via gravity-driven [[dry deposition]],<ref name="a.mpg.de" /> and the time it takes for the "[[Phoresis|phoretic effect]]" to move coagulated particles to a lower level in the atmosphere.<ref name="babel.hathitrust.org"/> Whether by coagulation or the phoretic effect, once the aerosol of smoke particles are at this lower atmospheric level, [[cloud seeding]] can begin, permitting [[precipitation (meteorology)|precipitation]] to wash the smoke aerosol out of the atmosphere by the [[wet deposition]] mechanism.

The [[Chemistry|chemical]] processes that affect the removal are dependent on the ability of [[atmospheric chemistry]] to [[oxidize]] the [[carbonaceous]] component of the smoke, via reactions with oxidative species such as [[ozone]] and [[nitrogen oxides]], both of which are found at all levels of the atmosphere,<ref>[http://www.atmosphere.mpg.de/enid/906c8d956939bb335e9b051e10f45223,0/4__Gases_in_the_atmosphere/-_Distribution___concentration__2__3tg.html Distribution & concentration (2)] {{webarchive| url=https://web.archive.org/web/20110727031921/http://www.atmosphere.mpg.de/enid/906c8d956939bb335e9b051e10f45223,0/4__Gases_in_the_atmosphere/-_Distribution___concentration__2__3tg.html |date=2011-07-27 }} Dr. Elmar Uherek – Max Planck Institute for Chemistry Mainz, April 6, 2004</ref><ref>{{harvnb|Toon|Turco|Robock|Bardeen|2007|p=1999}}. "At one time it was thought that carbonaceous aerosol might be consumed by reactions with ozone (Stephens et al., 1989) and other oxidants, reducing the lifetime of soot at stratospheric altitudes. However recent data shows that the reaction probability for such loss of soot is about 10^-11 so it is not an important process on times scales of several years (Kamm et al., 2004). A full simulation of stratospheric chemistry, along with additional laboratory studies, would be needed to evaluate the importance of these processes. Rate constants for a number of potentially important reactions are lacking."</ref> and which also occur at greater concentrations when air is heated to high temperatures.

Historical data on residence times of aerosols, albeit a [[atmospheric particulate matter|different mixture of aerosols]], in this case [[stratospheric sulfur aerosols]] and [[volcanic ash]] from [[megavolcano]] eruptions, appear to be in the one-to-two-year time scale,<ref>{{cite web |website=How Volcanoes Work |url=http://www.geology.sdsu.edu/how_volcanoes_work/climate_effects.html |access-date=2011-04-15 |archive-url=https://web.archive.org/web/20110423214804/http://www.geology.sdsu.edu/how_volcanoes_work/climate_effects.html| archive-date=2011-04-23|url-status=live|title=Climate Effect of Volcanic Eruptions}}</ref> however aerosol–atmosphere interactions are still poorly understood.<ref>{{cite web |author=Geerts |first=B. |title=Aerosols and climate |url=http://www-das.uwyo.edu/~geerts/cwx/notes/chap02/aerosol&climate.html |url-status=live |archive-url=https://web.archive.org/web/20190121203256/http://www-das.uwyo.edu/~geerts/cwx/notes/chap02/aerosol%26climate.html |archive-date=2019-01-21}}</ref><ref>{{cite web| url=http://gacp.giss.nasa.gov/|title=Global Aerosol Climatology Project| website=gacp.giss.nasa.gov |publisher=NASA |access-date=2011-04-15|url-status=live |archive-url=https://web.archive.org/web/20080523102619/http://gacp.giss.nasa.gov/|archive-date=2008-05-23}}</ref>

=== Soot properties ===
{{see also|Tihomir Novakov|Aethalometer}}
Sooty aerosols can have a wide range of properties, as well as complex shapes, making it difficult to determine their evolving atmospheric [[Optical depth#Atmospheric sciences|optical depth]] value. The conditions present during the creation of the soot are believed to be considerably important as to their final properties, with soot generated on the more efficient spectrum of [[stoichiometry|burning efficiency]] considered almost "elemental [[carbon black]]," while on the more inefficient end of the burning spectrum, greater quantities of [[Pyrolysis|partially burnt]]/oxidized fuel are present. These partially burnt "organics" as they are known, often form tar balls and [[brown carbon]] during common lower-intensity wildfires, and can also coat the purer black carbon particles.<ref>{{cite web| url=http://www.mtu.edu/news/stories/2013/august/new-insights-wildfire-smoke-could-improve-climate-change-models.html|title=New Insights on Wildfire Smoke Could Improve Climate Change Models|access-date=2014-11-03| archive-url=https://web.archive.org/web/20141104015918/http://www.mtu.edu/news/stories/2013/august/new-insights-wildfire-smoke-could-improve-climate-change-models.html|archive-date=2014-11-04|url-status=live|date=2013-08-27}}</ref><ref>{{cite web|url=http://www.abqjournal.com/440827/news/lanl-study-wildfire-smokes-effect-on-climate-underestimated.html|title=LANL study: Wildfire smoke's effect on climate underestimated|first=Olivier|last=Uyttebrouck|website=www.abqjournal.com|access-date=2014-11-03|archive-url=https://web.archive.org/web/20150627114118/http://www.abqjournal.com/440827/news/lanl-study-wildfire-smokes-effect-on-climate-underestimated.html|archive-date=2015-06-27|url-status=live}}</ref><ref>{{cite web |url=http://wildfiretoday.com/2013/07/17/research-wildland-fire-smoke-contributes-to-climate-change-more-than-previously-thought/|title=Research: wildland fire smoke, including tar balls, contribute to climate change more than previously thought - Wildfire Today|date=17 July 2013|access-date=3 November 2014|archive-url=https://web.archive.org/web/20140724224709/http://wildfiretoday.com/2013/07/17/research-wildland-fire-smoke-contributes-to-climate-change-more-than-previously-thought/|archive-date=24 July 2014|url-status=live}}</ref> However, as the soot of greatest importance is that which is injected to the highest altitudes by the pyroconvection of the firestorm – a fire being fed with storm-force winds of air – it is estimated that the majority of the soot under these conditions is the more oxidized black carbon.<ref>{{harvnb|Toon|Turco|Robock|Bardeen|2007|pp=1996–1997|loc="Optical properties of soot particles"}}. "mass fires are likely to completely oxidize the fuels that are readily available".</ref>