As we learn more about the climate system, we continue to discover additional humans and natural climate forcings occur. The August 17 2010 issue of EOS has an excellent article by Randy Showstack titled
which reports on such a climate forcing. Excerpts from the paper read
“Volcanic eruptions are not the only violent events that can inject smoke-colored and cauliflower-textured clouds into the stratosphere. Pyrocumulonimbus (pyroCB) storms can, too. These recently discovered phenomena are storms caused or aided by fire; they have many characteristics similar to thunderstorms, including lightning, hail, and extreme vertical height through the troposphere and into the lower stratosphere.”
“Common wisdom had held that “the only event that can explosively pollute the stratosphere is a volcanic eruption,” Michael Fromm, a meteorologist with the Naval Research Laboratory in Washington, D. C., said at a 9 August press briefing at the 2010 Meeting of the Americas in Foz do Iguaçu, Brazil. “Now we know that pyroCBs can do a version of this, thanks to the heat from fire.” Fromm is a coauthor of “The untold story of pyrocumulonimbus,” a paper to be published in the Bulletin of the American Meteorological Society.”
“The paper states that these events occur “surprisingly frequently”—with 17 now known to have occurred in Canada and the United States in 2002 alone…”
“Fromm said pyroCBs have a volcano-like impact on the stratosphere, injecting material ‘far enough into the stratosphere that particles and gases can remain for months.’”
“While volcanoes can affect global temperature because of the mass of stratospheric aerosols that can be created from some eruptions, Fromm explained that pyroCB events cannot compete with the biggest eruptions. He added that repeated smaller contributions of aerosols from pyroCBs “may be something that we need to pay attention to.”
The sources of these fires are from both natural events (e.g. a forest fire from lightning) and from human caused events (e.g. biomass burning for land clearing). The recognition that the aerosols associated with these thunderstorms can be ejected into the stratosphere and persist there for months clearly shows that pyrocumulonimbus have a significant climate effect both on the regional and global scales.