From the Australian bushfire crisis in 2019 to 2020 to the deadly wildfire outbreaks in California, wildfires are no longer episodic hazards but direct products of climate change.
The Australian bushfires alone—which scorched over 42 million acres of land and killed millions of animals and hundreds of people—are estimated to have ejected 1 million tons of smoke into Earth’s atmosphere, as high as 22 miles above the planet’s surface. In the aftermath, scientists discovered the fires helped increase global temperatures by 1 degree Celsius for about six months.
Even worse, however, the smoke punctured a large hole in the ozone right above Antarctica. For a while this has been inexplicable—scientists had no way of understanding how the two events could be connected. But in a new study published in the Proceedings of the National Academy of Sciences on Monday, atmospheric researchers at MIT show how smoke particles released by wildfires unleash a chemical chain reaction that decimates the ozone, creating another problem exacerbated by the effects of climate change.
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Ozone is the layer of gas in the stratosphere that deflects much of the sun’s harmful ultraviolet radiation. Without it, all life on Earth would be irradiated and the landscape would be turned into an apocalyptic wasteland. But even with the ozone, overexposure to UV light can lead to serious health conditions in humans, like skin cancer, premature aging, and even suppression of the immune system.
During the 1970s and 1980s, atmospheric scientists noticed the cushy layer of ozone was slowly thinning out as the decades passed. It was ultimately discovered chlorofluorocarbons (CFCs)—man-made molecules of carbon, chlorine, and fluorine first synthesized in 1928 for manufacturing, refrigerations, and air conditioning—were damaging the ozone layer. The international community rallied to curtail CFC use through the Montreal Protocol in 1987.
While wildfires don’t release CFCs, wildfire smoke carries chemicals into the atmosphere that react with other atmospheric compounds to produce chlorine compounds. In chemical reactions with volcanic eruptions, wet volcanic aerosols react with nitrogen-based chemicals floating around in the stratosphere. Some like dinitrogen pentoxide react with sunlight to form other nitrogenous chemicals, including one called nitrogen dioxide that binds to chlorine-containing chemicals also found in the stratosphere, Susan Solomon, an MIT atmospheric chemist and lead author of the new study, told The Daily Beast in an email.
As these chemical reactions proceed free-floating in the stratosphere, the number of nitrogen species decreases and the number of chlorine ones increase, Solomon said. As a result, they end up destroying the ozone layer.
To test whether this was likely the same in the case of the Australian wildfires, Solomon and her team checked out nitrogen dioxide levels dropped around the time of the wildfires. Multiple instruments verified they had, including one that indicated nitrogen dioxide values were at the lowest in 20 years during the fires.
Furthermore, Solomon and her team built a model of atmospheric chemistry that seemed to strongly suggest the decrease in nitrogen dioxide was only really possible as a result of wildfire smoke—no other variable could account for what the satellite data showed.
Solomon acknowledged that while the chemical behavior exhibited by wildfire smoke may not be the whole story—there could be other chemical reactions contributing in tandem—she said her team’s findings show “that the behavior of these [smoke particles] with regard to nitrogen dioxide is very similar to what occurs on volcanic particles.” Solomon and her group plan to extend their findings to examine the impact of other recent wildfires, like those in California, on the ozone.
These findings were published just a week after a new UN report warned that wildfires are expected to grow “more intense and more frequent” in the coming decades as global warming intensifies. As climate change worsens over time, we’re finding new ways that our environment is degrading and putting people at risk. Though most of the world is safe from wildfires, their contribution to ozone depletion puts the entire world in danger—raising the urgency for us to take meaningful action against climate destruction.
