Black carbon lofts wildfire smoke high into the stratosphere to form a persistent plume | Science

[Andrew Lockley]

https://science.sciencemag.org/content/365/6453/587.full

Black carbon lofts wildfire smoke high into the stratosphere to form a persistent plume

Pengfei Yu1,2,3,*, Owen B. Toon4,5, Charles G. Bardeen6, Yunqian Zhu5, Karen H. Rosenlof2, Robert W. Portmann2, Troy D. Thornberry1,2, Ru-Shan Gao2, Sean M. Davis2, Eric T. Wolf5,7, Joost de Gouw1,8, David A. Peterson9, Michael D. Fromm10, Alan Robock11

 See all authors and affiliations

Science 09 Aug 2019:

Vol. 365, Issue 6453, pp. 587-590

DOI: 10.1126/science.aax1748

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Up in smoke

Extensive and intense wildfires in the Pacific Northwest of the United States in 2017 injected large quantities of smoke into the stratosphere. Yu et al. used satellite observations and modeling to characterize the history and chemistry of that smoke. The smoke rose to altitudes between 12 and 23 kilometers within 2 months owing to solar heating of black carbon. The smoke then remained in the stratosphere for more than 8 months. Photochemical loss of organic carbon resulted in a smoke lifetime 40% shorter than expected.

Science, this issue p. 587

Abstract

In 2017, western Canadian wildfires injected smoke into the stratosphere that was detectable by satellites for more than 8 months. The smoke plume rose from 12 to 23 kilometers within 2 months owing to solar heating of black carbon, extending the lifetime and latitudinal spread. Comparisons of model simulations to the rate of observed lofting indicate that 2% of the smoke mass was black carbon. The observed smoke lifetime in the stratosphere was 40% shorter than calculated with a standard model that does not consider photochemical loss of organic carbon. Photochemistry is represented by using an empirical ozone-organics reaction probability that matches the observed smoke decay. The observed rapid plume rise, latitudinal spread, and photochemical reactions provide new insights into potential global climate impacts from nuclear war.

[Russell Seitz]

The most interesting new insight this paper affords is that it confirms the "once in a blue moon" rarity of stratospheric smoke injections. The orignal 1983 TTAPS paper-  Owen Toon is the second T, presumed their ubiquity, and postulated that teragrams of black smoke from thousands of fires  lit by nuclear attacks would simultaneously rise past the tropopause, creating a hemispheric optical depth of 20 and by reducing sunlight by  roughly 3 to 6  orders of magnitude,creating a lethal global deep freezelasting for months or years. 

Climate communicator Carl Sagan, the S in TTAPS publically equated the modeled effects with those of the K-T asteroid impact and wrote that " The extinction of Homo sapiens cannot be excluded."  and pronounced  what he termed his "Apocalyptic predictions" to be the "robust" products of a "sophisticated one dimensional model."  Writing in Foreign Affairs asserted that , never mind the smoke, the dust alone from a nuclear exchange 100 time smaller that TTAPS apocalyptic  "baseline" case,  "a (100 megaton) pure tactical war in Europe" would be equally dire.

Forest fire experiments were accordingly carried out in Canada  in the 80's to test TTAPS 'nuclear winter' hypothesis but did not produce high optical depths or evidence of solar plume bouyancy or stratospheric smoke transport-  it has taken three decades for one natural wildfire  out of hundreds to do so. Black smoke from the appallingly intense Kuwait Oil Fires also failed to penetrate the tropopause.although Sagan warned ABC Nightline viewers would collapse the Asian monsoon , causing a regional famine. It didn't happen.

There was once a case for climate modeling hyperbole in the service of disarmament, but the Cold War is long gone, and while Alan Robock remains  at liberty to call radiative forcing , and single digit temperature changes , from low optical depth model intercomparisons, "nuclear winter ",but  the  two most salient feature of this study are that, as was objected in the 1980's, photochemisry militates against  othe optical depth persistance, TTAPS presumed in adducing the term 'nuclear winter" and that smoke plumes that reach the stratosphere remaiin quite rare-  we had to wait more than a generation for satellites to catch one in the act. 

It's easy  to paint a GCM l sky black- just tell the systems programmer to adjust the code, but models are not things and the material world is under no obligation to emulate that parameter changes that we make .

CF

https://www.nature.com/articles/475037b

[Russell Seitz]

Spellchecked & edited repost of the above:

The most interesting insight in Yu, Toon,  Robock,  et al.'s  paper is its confirmation of the "once in a blue moon" rarity of stratospheric smoke injections. 

The orignal 1983 TTAPS paper- Owen Toon is the second T, presumed stratospheric injection would be the norm, and postulated that teragrams of black smoke from thousands of nuclear attack  fires would simultaneously rise past the tropopause, creating a hemispheric optical depth of up to  20,  reducing sunlight by  roughly 3 to 6  orders of magnitude, dropping surface temperatures by tens of degrees to create a lethal global deep freeze lasting for months or years. 

Climate communicator Carl Sagan, the S in TTAPS,  publicly equated the modeled effects with those of the K-T asteroid impact and wrote that:

 " The extinction of Homo sapiens cannot be excluded."  

He asserted his "Apocalyptic predictions" to be the "robust" products of a "sophisticated one dimensional model." and wrote  in Foreign Affairs  that , never mind the smoke,  cooling from dust alone. even from a 50 megaton a nuclear war 100 times smaller that TTAPS 5,000 megaton "baseline" case would produce equally dire effects.

Forest fire experiments were accordingly carried out in Canada  in the 80's to test TTAPS 'nuclear winter' hypothesis but they failed to produce produce high optical depths or evidence of solar plume bouyancy or stratospheric smoke transport. It took three decades before one natural wildfire out of hundreds produced either.

Black smoke from the appallingly intense Kuwait Oil Fires also failed to penetrate the tropopause. although Sagan warned ABC Nightline viewers that their emissions would collapse the Asian monsoon and cause a regional famine. It didn't happen.

There was once a case for climate modeling hyperbole in the service of disarmament, but the Cold War is long gone. While  Alan Robock remains  at liberty to call radiative forcing , and single digit temperature changes  from   more modern and realistic  low optical depth GCM  model intercomparisons, "nuclear winter ", the  two most salient feature of this study are that, as was objected in the 1980's, photochemisry militates against  the ooptical depth persistance that  TTAPS presumed in adducing the term 'nuclear winter.

Smoke plumes that reach the stratosphere remaiin rare outliers-  we had to wait more than a generation for satellites to catch one in the act. 

While it is  easy  to paint  a model's  sky black- just tell the systems programmer to adjust the code, models are not things ,and the material world is under no obligation to emulate parameters chosen or guessed at in the name of the precautionary principle.  

TTAPS and the term 'nuclear winter were criticized as just such a case by climate modelers and statregic policy analyst alike, notably Climatic Change founder  Steve Schneider, and John Holdren's predecessor as Pugwash president, George Rathjens of MIT.

CF

https://www.nature.com/articles/475037b