The view from below
A dense haze overspread Chile and western Argentina on Monday morning, yielding smoky sunshine and probably enhancing sunset colors in a number of places.
“It’s possible to see the effects of aerosol[s] in the atmosphere with redder than usual sunsets,” said David Moore, a scientist at the U.K. National Center for Earth Observation, in an email. “I wouldn’t be surprised if some reports to that effect come out of South America soon. People may also start reporting smelling smoke.”
Webcams revealed haze limiting visibility in Santiago, Chile on Monday afternoon. Smog near the surface is possible from vehicle traffic/industry with some contribution from domestic wildfires, but the milky-white sky above is connected to the events in Australia.
And the particles lofted high into the atmosphere from the Australian wildfires won’t stop there. After being blasted to extreme heights by the heat of the blazes, they’ll continue their march around the globe.
Fire emissions blasted to high altitudes
Thanks to the Australian wildfires, aerosols and other chemicals are being lofted high into the atmosphere. Aerosols are very fine solid or liquid particles suspended in a gas. Pollen, dust, soot and even sea salt spray are considered aerosols.
In some cases, aerosols originating from the fires have been deposited into the stratosphere. That’s the next layer of the atmosphere atop the troposphere, in which we live.
From there, the particulates are free to surf the jet stream across the planet.
The high-altitude transport is courtesy of pyrocumulonimbus clouds menacing eastern Australia on the most severe bush fire days. These fire-triggered thunderheads are like an elevator for carrying materials to altitudes where they’d seldom otherwise venture, outside of a volcanic eruption, that is.
“These clouds can provide a direct pathway for smoke aerosols to reach the stratosphere,” Moore said. “Once these aerosols reach the stratosphere, they can hang around for weeks/months, comparable really to what happens after moderately powerful volcanic eruptions.”
Neil Lareau, an assistant professor of atmospheric sciences at the University of Nevada at Reno, says the fire-induced thunderstorms are a key contributor to fire emissions to the upper atmosphere. Pyrocumulonimbus clouds “have put stuff into the stratosphere that [has] been tracked for months,” Lareau said in an interview.
“What I’m finding most remarkable about the fires so far is the amount of aerosol reaching the stratosphere from this event,” explained Moore, who also was amazed by the scope of the chemical transport.
Moore said this event appears to be similar in magnitude to wildfires in Canada in 2017, and a tragic 2009 bush fire event in Australia known as “Black Saturday.”
“Apart from those two, I don’t think I’ve seen anything on this scale in the stratosphere caused by wildfires in the past 20 years as an atmospheric scientist,” he said.
Circumnavigating the globe in weeks
It only takes a few weeks for air to circumnavigate the globe in a single latitude band; less time is required near the poles, more as you get closer to the equator. Transport between the two hemispheres — in this case for the pollutants to make it into the Northern Hemisphere — would take closer to a year.
“This sort of long-range transport happens more regularly than you might think,” Moore said.
What’s especially remarkable in the case of the Australian bush fires is how long the smoke plume continues to remain intact before dispersing — in some cases, a thick, narrow filament of smoke is visible for some 4,000 or 5,000 miles.
That’s a testament to the sheer volume of smoke produced, and the scale of the wildfires giving rise to them.
For the smoke to remain visible to the naked eye some 7,000 miles away from its source, as was the case Monday morning in Chile, is unusual, since such particles typically disperse into the surrounding air closer to their source.
“The smoke transport from Australia to South America … really reflects the intensity of the fire activity over the last week or so, where [huge] amounts of smoke have been emitted,” said Mark Parrington, a senior scientist at the European Center for Medium-Range Weather Forecasts specializing in global air quality and wildfires, in an email.
“I did see images from Chile and Argentina of red skies related to the smoke transport.”
The climate effects
Aerosol injection into the stratosphere can have a number of climate effects. Often, exact impacts depend on the specific aerosol released as well as the altitude.
“For volcanoes it is the [sulfur dioxide] released which reacts with water in the stratosphere to create sulfate aerosol[s] which can hang around for weeks, months, sometimes years (Pinatubo 1991)," said Moore, referring to the eruption of a volcano in the Philippines, that helped damp global temperatures for up to two years afterward.
“Sulfate aerosols reflect sunlight and have a cooling effect on the climate which can persist up to a couple of years,” he said.
In this case, however, the Australian fires are rich in carbon. However, the role of stratospheric carbon is poorly understood.
According to Moore, research is ongoing into whether carbon-rich aerosols in the stratosphere would have a cooling or warming effect on the planet. Recent studies, he said, lean toward a warming influence.
In addition to the aerosols, the fires are releasing greenhouse gases in the forms of carbon dioxide and methane, that had been stored by the forests that are going up in flames, which worsens global warming.
Andrew Freedman contributed to this report.