Towering wildfire clouds are affecting the stratosphere and climate
On August 8, 2019, the Williams Flats Fire in northeastern Washington state produced a fire cloud, or pyroCb, that ejected smoke into the stratosphere. A NASA plane flew in to investigate. (David Peterson, NRL)
In recent years, amid record-breaking wildfires in the western United States and elsewhere, the sight of vast swathes of wildfire smoke rising into the sky has become commonplace. Now, a team of atmospheric scientists has demonstrated that these plumes have a major impact on the stratosphere and climate.The result is just published in a magazine science.
Large wildfires can lift smoke to enormous heights. Known as pyrocumulonimbus, or pyroCbs, these towering clouds are created when the heat of wildfires triggers massive thunderstorms that carry smoke into the stratosphere five to seven miles above the surface.
In 2017, a american airborne mission Study of the atmosphere over a remote ocean intersected by smoke from a giant pyroCb event in the Pacific Northwest. The smog was so widespread that remote-sensing instruments around the world monitored it for more than eight months. Measurements show that it and several other pyroCb events in the northern hemisphere that year dominated the contribution of black carbon and organic carbon to the lower stratosphere, surpassing human emissions from vehicles, industry, heating, cooking and agricultural land reclamation. The net effect is to cool the planet.
“Fire-fueled thunderstorms are getting bigger and more frequent—witnessing record-breaking events in 2017, 2019, and 2020,” said study co-author Josh Yau, of the National Oceanic and Atmospheric Administration, who led the study Yaschwartz said. “Their recent impact on the stratosphere has been impressive.”
“We knew that fires release large amounts of aerosols. But we didn’t realize that these aerosols could be ejected so high into the atmosphere,” said the atmospheric chemist and study co-author Conman Resin Columbia Climate School’s Lamont-Doherty Earth Observatory. Commane flies long-distance missions over oceans to capture data on aerosols.
Scientists are interested in learning more about pyroCbs because their smoke lingers in the atmosphere longer than typical fires produce. The research should also provide insights into the behavior of aerosols produced by volcanoes, aviation or potential future solar geoengineering efforts.
So far, critical measurements of these giant clouds have been limited because of their highly sporadic nature and the logistical challenges of getting scientific instruments airborne and into the smoke in a short amount of time. Consequently, little is known about the distribution and duration of smoke from these events and the overall impact on climate and stratospheric aerosol chemistry, including the ozone layer.
A surprising finding of the study was the discovery of an extremely thick coating of other chemicals on solid black carbon particles produced by wildfires.Scientists aren’t quite sure how the sticky coating forms, but it appears to be composed of organic aerosols and gases that condense on the particles as the smoke rapidly rises and cools in the atmosphere, say Study co-author Kara Lamb Columbia Institute for Data Science.
A recent airborne mission Provides direct samples of pyroCb smoke that lasted for several hours from the 2019 Williams Flats Fire in Northeast Washington State. An analysis of black carbon from that fire gave the researchers more confidence in the conclusions drawn from the 2017 smoke.
The thick coating on the black carbon particles, along with their size and mass, is such a stable feature of pyroCb smoke that the researchers realized they could be used to “fingerprint” these particles in the lower stratosphere. Using these fingerprints, they re-examined data from a total of 12 previous airborne mission datasets since 2006 to estimate the long-term impact of pyroCb on recent climate in the lower stratosphere.
They found that even in years with relatively little fire charcoal ahead of the more active fire season that began in 2020, the effect of smoke was large, accounting for all stratospheric black and organic carbon in the lower stratosphere over the past decade. about 20% of that.
“This gives us a reasonable estimate representing the period before things really started to light up,” Schwartz said. “We now recognize the long-term impact of pyroCbs on the stratosphere. It’s not just an important blip, but a steady-state impact that needs to be considered.”
Adapted from a NOAA press release.
