Clouds from large forest fires cause long-term effects in the stratosphere. Research on PiroCbs

 'Flammagenitus' or as they are more commonly known ''Pyrocumilonimbus' (PyroCbs) is name given to the  thunderstorm that forms in the smoke plume of a fire (nuclear bomb blast or volcanic ash cloud). The large plumes of smoke generated during massive fires on the Earth's surface or volcanic eruptions, ..... when they reach a certain magnitude, they are capable of generating large vertical clouds that cause meteorological phenomena such as electrical storms and tornadoes. In the case of a forest fire, the intense heat source generates hot air that rises upwards, mixing gases, smoke particles, and the energy released through the condensation, water vapour and ice particles that helps creating the lighning which increases the risk of generating more and larger fires (J.M Katich et al. 2023). These substances have a direct impact on the climate system.

Initially, in the 2000s, when the existence of PyroCbs became of interest to researchers, it was considered that only extreme weather phenomena arising from natural causes (atmospheric storms, volcanic eruptions) could expel particles and material that reach so high in the stratosphere. It has now been demonstrated that large anthropogenically generated fires can also produce thick layers of black carbon particles in the upper layers of the atmosphere. Michael Fromm, together with other researchers such as René Servranckx were the first able to prove the existence of PyroCbs (Michael Fromm, Daniel T. Lindsey, René Servranckx, Glenn Yue, Thomas Trickl, et al.. 2010). 

NASA was the first organisation to carry out an in-depth study of PyroCbs, Atmospheric Tomography Mission (ATOM) took place between July 2016 and the end of May 2018. A NASA DC-8 aircraft carried out four scans in remote areas over the Pacific, Atlantic, Antarctic, and Arctic oceans to sample the troposphere and lower stratosphere. The aim was to analyze how tropospheric air is affected by anthropogenic pollution. The largest PyroCbs phenomenon ever monitored was detected, coinciding with a series of massive wildfires in British Columbia, Canada, in the summer of 2017. Measurements of PyroCbs have so far been scarce. Their extent and duration were not known until recently. It is now known that they generate more carbon dioxide in the atmosphere than other human activities, such as traffic, industrial emissions, etc. 

A second study, known as FIREX-AQ, was conducted jointly by NOAA and NASA in 2019 monitoring PyroCb during the William Flats fire (Washington State) in 2019. This second investigation corroborated the hypotheses put forward during  ATOM  that forest fires may have an increasing impact on the regional climate. Aerosols emitted by forest fires affect both airquality and climate. Aerosol particles with an aerodynamic diameter of less than 2.5 microns (PM 2.5) have been associated with increased mortality in human populations and an increase in cases of respiratoy diseases, as wildfire activity intensifies, thus posing a risk to human health. (Wilmot, Taylor Y. & Mallia Derek V. & Hallar A. Ganner & Linn, John C. 2022). The 'World Air Quality Report 2019' also shown that Australian cities affected by the wildfires exceed  the safe limit for PM 2.5 in 78%. In terms of climate, aerosol loading from wildfires has a direct radiative impact due to the black carbon and organic aerosols absorbing and scattering incoming solar radiation respectively. Additionally, aerosols emitted during wildfires generate indirect radiative effects by altering cloud microphysics, On the other side, the conditions associated with pyrocumulonimbus cloud formation may continue to become more dangerous due to the climate change. (Wilmot, Taylor Y. & Mallia Derek V. & Hallar A. Ganner & Linn, John C. (2022).

Massive wildfires in the last 7 years

The massive fires in Australia in the summer of 2020, which burned more than 26.4 million hectares of land, offered new insights into the extent and size of these PyroCbs. According to the research (Peterson, D.A., Fromm, M.D., McRae. 2021), the aerosols generated by these fires were comparable to those from the Calbuco volcano eruption in Chile in 2015.  Another of the largest Pyrocubs ever recorded was on June 30th, at the Spark Lake fire in Western Canada. It generated a 160 km2 storm and spewed plumes of smoke at an altitude of 16 km into the lower stratospheric (altitude 10-15 km). Climate change and land-use change are projected to make wildfires more frequent and intense in most regions of the world (Sullivan, A., Baker, E. & Kurvits, T., 2022). 

The restoration of ecosystems is an important avenue to mitigate the risk of wildfires before they occur and to build back better in their aftermath. Wetlands restoration and the reintroduction of species, see the example of  beavers in Western USA (Fairfax Emily, Wittle Andrew, 2021), peatlands restoration, building at a distance from vegetation and preserving open space buffers are some examples of the essential investments into prevention, preparedness and recovery.

Reference list 

Das, S., Colarco, P. R., Oman, L. D., Taha, G., and Torres, O.: The long-term transport and radiative impacts of the 2017 British Columbia pyrocumulonimbus smoke aerosols in the stratosphere, Atmos. Chem. Phys., 21, 12069–12090,https://doi.org/10.5194/acp-21-12069-2021, 2021.

Fairfax, Emily & Whittle Andrew (2021), 'Smokey the Beaver: Beaver‐Dammed Riparian Corridors Stay Green During Wildfire Throughout the Western USA', The Bulletin of the Ecological Society of America, 102 (1),   https://doi.org/10.1002/eap.2225. 

J. M Katich, E. C. Apel, I. Bourgeois, C.A. Brock, T.P Bui, P. Campuzano-Jost, R. Commane, B. Daube, M. Dollner, M. Fromm, K.D. Froyd, A. J. Hills, R.S. Hornbrook, J.L. Jimenez, A. Kupc, K.D. Lamb, K. Mckain, F. Moore, D.M Murphy, B. A. Nault, J. Peischl, A. E. Perring, D. A. Peterson, E. A. Ray, K. H. Rosenlof, T. Ryerson, G. P. Schill, J. C. Schroder, B. Weinzierl, C. Thompson, C.J Williamson, S.C. Wofsy, P. Yu and J. P. Schawrz. 2023 . 'Pyrocumulonimbus affect average stratospheric aerosol composition'. Science Magazine. Vol 379, Issue 6634.  pp. 815-820.  DOI: 10.1126/science.add3101 

Michael Fromm, Daniel T. Lindsey, René Servranckx, Glenn Yue, Thomas Trickl, et al.. The untold story of pyrocumulonimbus. Bulletin of the American Meteorological Society, 2010, 91 (9), pp.1193- 1209. DOI: 10.1175/2010BAMS3004.1 

Peterson, D.A., Fromm, M.D., McRae, R.H.D. et al. Australia’s Black Summer pyrocumulonimbus super outbreak reveals potential for increasingly extreme stratospheric smoke events. npj Clim Atmos Sci 4, 38 (2021). https://doi.org/10.1038/s41612-021-00192-9

Sullivan, A., Baker, E. & Kurvits, T., 2022. Spreading Like Wildfire: The Rising Threat of Extraordinary Landscape Fires, UNEP and GRID Arendal. Kenya. Retrieved from https://policycommons.net/artifacts/2259313/wildfire_rra/3017991/ on 21 Mar 2023. CID: 20.500.12592/8qbg5j.

 Wilmot, Taylor Y. & Mallia Derek V. & Hallar A. Ganner & Linn, John C. (2022), 'Wildfire plumes in the Western US are reaching greater heights and injecting more aerosols aloft as wildfire activity intensifies', Scientific Reports, 12 (1),  2045-2322, https://doi.org/10.1038/s41598-022-16607-3.  

Last Updated: 23 March 2023