- Researchers observe how pyrocumulonimbus clouds form by a rising thermal from a fire.
- They studied wildfires that occurred in the Pacific Northwest in August 2017.
- Up to 50% of the ozone layer depleted over some parts of Canada.
Wildfire is attracting a lot of attention these days. People have realized that alterations in the occurrence frequency and intensity of wildfires could have significant consequences.
However, one of the most crucial aspects of wildfire behavior is still poorly understood — cumulonimbus flammagenitus cloud, also called pyrocumulonimbus cloud. It’s a type of dense towering vertical cloud that forms above the heat source such as a volcanic eruption or wildfire.
For the first time, researchers have observed how these clouds form by a rising thermal from a fire and how they get high enough (up to 14 miles into the air) to affect the protective ozone layer.
They studied wildfires that occurred in the Pacific Northwest in August 2017. Unlike most wildfire, this event injected pyrocumulonimbus clouds 7-14 miles up into the stratosphere. The dense smoke was observed in the stratosphere for an exceptionally long time (over 8 months).
The team used ground-based remote sensing, weather balloons and satellites to track smoke over the Northern Hemisphere. They measured the levels of organics and impure carbon particles called soot.
Reference: ScienceMag | DOI:10.1126/science.aax1748
New Insights Into The Chemistry Of Wildfire
Previous computer simulations have shown what would happen if excessive quantities of smoke were pushed into the stratosphere via nuclear weapons.
In 2017, the experiment was carried out by nature itself.
In these western Canadian wildfires, researchers were able to directly observe a process called ‘self-lofting’. The findings confirmed that a burning city would eject enough smoke into the stratosphere to have severe long-lasting climatic consequences.
This includes blocking out sunlight and damaging the ozone layer, which filters the shorter wavelength and highly hazardous ultraviolet radiation from the Sun.
A wildfire burns on a mountain in the distance east of Cache Creek | Credit: The Canadian Press 2017 / Darryl Dyck
As long as the smoke remains in the stratosphere, its constituents (organics and soot) absorb sunlight or send it back into space. This causes the hemispheric dimming effect, which eventually leads to crop shortage and failure.
Although most wildfires don’t cause a hemispheric dimming effect, they do push out ozone-rich air in that region. Researchers used the CALIPSO satellite to measure the ozone losses. They found that during the 2017 wildfires, up to 50% of the ozone layer depleted over some parts of Canada.
In summary, the analysis of smoke’s latitudinal spread and photochemical reactions during the 2017 wildfires offer new insights into possible climate impacts from nuclear war.
And since climate change is increasing the occurrence of such wildfires, especially in areas like the North American West, we may see denser fire clouds reaching the stratosphere.