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Australia is setting fire to damaged ozone layer and warmed stratosphere, study finds

By on August 25, 2022 0

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Australia’s fire season in late 2019 and early 2020 was extreme. It blew smoke about 20 miles into the sky, much like what a nuclear explosion might cause. Smoke from the fires circled the globe and hovered in plumes over the Pacific.

Now, a new study published Thursday in the journal Scientific Reports suggests that smoky aerosols caused the highest temperatures in the stratosphere in about three decades and likely damaged the ozone layer – which has been slowly recovering since substances that deplete it were largely eliminated by the 1987 Montreal Protocol.

The stratosphere, just above where planes fly, normally does not vary much in temperature due to events on the Earth’s surface – with the exception of volcanic eruptions.

But a sudden and unexpected warming of the global stratosphere has been detected in the first months of 2020, reaching up to 3 degrees Celsius around Australia and around 0.7 degrees Celsius globally. Researchers say this is the highest temperature recorded in the stratosphere since Mount Pinatubo in the Philippines erupted in 1991, sending aerosols of sulphate and smoke into the air.

Lilly Damany-Pearce, a researcher at the University of Exeter in England who led the study, said stratospheric warming and a large hole in the ozone layer stretching over most of the Antarctic continent in 2020 were likely to have been caused by the severe fire-induced storm clouds, or “pyrocumulonimbus” events, which injected huge plumes of smoke into the lower stratosphere.

She said smoke particles are about 50 times more effective at absorbing sunlight than volcanic sulfate particles – due to the black soot in smoke aerosols. Sunlight heats the air containing the smoke particles, causing this smoke-laden air to rise in a process similar to that which raises hot air balloons.

Once in the stratosphere, the researchers said, continued heating can cause changes in ozone through changes in atmospheric circulation, and chemical reactions on the surface of smoke particles can deplete the ozone layer.

“It is plausible that the good work being done under the Montreal Protocol … could be undone by the impact of global warming on intense fires,” said study co-author Jim Haywood, a scientist from the atmosphere at the University of Exeter, in an email.

The ozone layer helps absorb incoming ultraviolet radiation from the sun, protecting life on Earth from its harmful effects, such as skin cancer and the formation of cataracts. The hole in the ozone layer that formed over Antarctica following the 2020 fires was the longest lasting and among the largest and deepest in decades, according to the World Meteorological Organization.

The Tonga volcano threw an unprecedented amount of water into the atmosphere

Olaf Morgenstern, a scientist at New Zealand’s National Institute for Water and Atmospheric Research, said the impact of Australia’s fires on the stratosphere – including a plume of smoke that drifted over the Pacific Southeast “unprecedented in sighting records”.

Morgenstern, who was not involved in the study, explained that smoke aerosols don’t stay in the upper atmosphere as long as harmful man-made chemicals, which can linger in the atmosphere for up to 80 years old.

“The big issue here is that, as part of global warming, the frequency and intensity of wildfires are expected to increase, leading to more” fire-induced stratospheric warming and depletion ozone in the future, Haywood said.

“I don’t believe it’s a coincidence that we had these massive fires in Australia. They are part of the trend”, Morgenstern said showing this last summer of devastating fires in Europe – also fueled by similar waves of extreme heat and widespread drought conditions that led to the Black Summer Fires in Australia.

Previous research has shown that the 2020 Australian fire season was so extreme that it modified large-scale wind patterns more than 10 miles above our heads. Another study last year observed temperature and ozone changes from satellite data.

The great contribution of the last article, according to Martin Juckera climate expert at Australia’s University of New South Wales who was not involved in the study, is that the researchers put satellite observations from the period into a state-of-the-art climate model “to prove that the bushfires were in fact the reason for what we observed.”

“Heating the stratosphere doesn’t really have a direct impact for us on the surface. [of the Earth], but preventing ozone from recovering or destroying ozone for a year has a real impact on the surface,” he said. “Before the 2019 bushfires, I don’t think we even thought [fires] could have such an impact. That a bushfire can have as much impact as a volcano.