Recent Megafire Smoke Columns Have Reached the Stratosphere, Threatening Earth’s Ozone Shield

Scientists researching how the recent spike in extreme wildfires affects the climate say that just a few weeks of smoke surging high into the stratosphere from one intense fire can wipe out years of progress restoring Earth’s life-protecting ozone layer. 

Close study of Australia’s intense Black Summer fires in late 2019 and early 2020 suggests the smoke they emitted was a “tremendous kick” to the atmosphere, depleting the ozone layer by 1 percent, said MIT scientist Susan Solomon.

“The ozone layer protects all life on the planet from ultraviolet radiation,” said Solomon, who was one of the pioneers in explaining how pollution depletes ozone while she was a researcher with the National Oceanic and Atmospheric Administration. “You know that, if you’ve ever been sunburned, it increases the risk of skin cancer and eye damage.”

“Of course if it does those things to you, you can only imagine what it does to plants and animals,” she added. With numerous studies showing how UV radiation can damage certain crops and other plants, there is “good reason to be worried about safeguarding the ozone layer in a healthy state.”

The impacts of declining atmospheric ozone are not isolated to the poles.

“What worries me is, it’s not just Antarctica,” she said. “If you talk about Australia, where these fires were, we see something like a 5 to 10 percent decrease in ozone over mid-latitude locations, and every 1 percent loss gives you a 2 percent increase in skin cancer.”

Scientists have recognized threats to the ozone layer from reactive chemicals used in commercial and industrial processes since at least since the 1970s, and have spent a lot of time trying to make sure society understands the chemistry, she said. “This isn’t a new thing to those of us who have been studying it,” she said. “This is not our first rodeo.”

One of the key advances came when scientists started looking at how atmospheric chemistry can be changed by external contaminants like industrial pollution and wildfire smoke, rather than just through internal atmospheric processes. 

Solomon said scientists already knew that various pollutants can change atmospheric chemistry at lower altitudes, but were surprised to find reactive particles in the stratosphere.

“We didn’t realize at first how important that could be in the very dry stratosphere,” she said. “The discovery of the Antarctic ozone hole is what woke us up to that fact.”

The Black Summer fires’ depletion of 1 percent of atmospheric ozone, as documented by Solomon and other scientists in a Feb. 28 study in the Proceedings of the National Academies of Sciences, may seem like a small number, she said, but “it’s significant to me because it’s comparable to the 1 percent per decade progress that world has achieved with the Montreal Protocol.”

She said that, while the wildfire smoke’s impacts in the stratosphere don’t last anywhere as long as those from industrial chemical pollutants, the concerns remain because extreme wildfire activity is expected to increase by 30 percent by 2050 and 50 percent by the end of this century. 

In some regions of the U.S., wildfires since 2000 have already increased up to four times in size and three times in frequency during the previous two decades, and there are more frequent simultaneous large fires in different regions, according to new research published in Science Advances. 

Australia’s Black Summer fires were followed by similarly intense wildfires in Western North America, that also triggered towering pyrocumulonimbus clouds that transported smoke miles up into the stratosphere, where it could degrade the ozone layer. A 2005 study looked at a fire in Canada’s Northwest Territories that sent a smoke plume into the stratosphere, 

More recently, ship-based Arctic researchers reported that smoke from Siberian wildfires in the summer of 2019 persisted in the high atmosphere for much of the winter, and may have contributed to record-setting Arctic ozone depletion during the 2019-2020 winter.

In the past decade, extreme fires have burned somewhere on the planet nearly every year, most recently in South America, where fires in late December and January were measured as some of the most intense on record on that continent by Copernicus, the European Union’s climate monitoring agency. 

New Satellite Data Help Pinpoint Impacts

Another new study on wildfire smoke and ozone published today in Science suggests that the 1 percent loss shown in Solomon’s research may be the far lower limit of what could be expected in ozone depletion from wildfire smoke in the stratosphere, Solomon said. 

That research, led by Peter Bernath of Waterloo University, analyzed data from super-sensitive optical instruments from a Canadian satellite that peers at the upper edge of the planet’s atmosphere against a sunlit backdrop to measure chemical reactions involving smoke particles and atmospheric gases. By studying 44 types of particles, the researchers may be able to at least partly determine the future impact of wildfire smoke on ozone.

“In a nutshell,” Bernath said, “the chlorine chemistry in particular is altered. The smoke converts various chlorine-based molecules into more active compounds that end up destroying ozone. These megafires are unique in that they punch right into the stratosphere and deliver organic compounds, putting the smoke particles right where they can catalyze these harmful changes.”

The study also focused on the Black Summer fires and showed that smoke produced “unexpected and extreme perturbations in stratospheric gases beyond any seen in the previous 15 years of measurements,” the researchers said. The observations suggest that, as severe wildfires become more frequent, their effects will become an increasingly important factor in the global ozone budget of the future.

“Nobody ever saw these changes before, nobody suspected the smoke would cause these kinds of changes,” he said, adding that the effect was widespread over the mid-latitudes of the Southern Hemisphere, as prevailing winds carried the smoke around the globe.

As global warming leads to stronger, more frequent wildfires, the smoke could have a serious, lasting impact on ozone, Solomon said.

“Wildfire smoke is a toxic brew of organic compounds that are complex beasts,” she said. “And I’m afraid ozone is getting pummeled by a whole series of reactions that we are now furiously working to unravel.”