Australia's epic wildfires expanded ozone hole and cranked up global heat

[Uncle Joe]

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Extreme drought in 2019 gave rise to bush fires of unprecedented intensity, which burnt more than 5.8 million hectares. In addition to causing catastrophic damage, the fires generated plumes of smoke that rose into the atmosphere and bumped up temperatures in the lower stratosphere over Australia by 3 °C. Globally, temperatures in the lower stratosphere rose by 0.7 °C — the biggest increase since the eruption of Mount Pinatubo in the Philippines in 1991 sent a plume of ash into the atmosphere, says the study, which was published in Scientific Reports on 25 August. The temperature boost lasted for around four months.

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Smoke in the stratosphere

The stratosphere sits between roughly 10 and 50 kilometres above Earth’s surface. Smoke particles don’t typically get to the stratosphere, but smoke from the Australian fires reached heights of more than 35 kilometres owing to unusual, fire-induced pyrocumulonimbus clouds. These smoke-infused thunder clouds hold lots of black carbon, which absorbs heat and rises into the lower stratosphere like a hot-air balloon, says study co-author Jim Haywood, an atmospheric scientist at the University of Exeter, UK. Once there, the black carbon continues to absorb sunlight and warm the air.

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Damaged ozone layer

The models also indicated that chemical reactions between the smoke and ozone in the atmosphere exacerbated the Antarctic ozone hole, making it bigger. “The year before the fires, we had a puny little ozone hole,” says Haywood. “In 2020, we were taken rather aback because there was a very, very deep ozone hole.” He says the hole lasted for around five months.

Depletion of the ozone layer strengthens the southern polar vortex, a pocket of low pressure and cool air over the South Pole. That creates a feedback loop: the stronger the polar vortex is, the more it depletes the surrounding ozone and the longer it keeps the hole open for. When the ozone layer is damaged, more radiation from the Sun gets through to Earth, causing harm to the environment and human health. Warming in the stratosphere can also lead to ozone-layer damage, by altering the atmosphere’s dynamics.


https://www.nature.com/articles/d41586-022-02782-w