Wild fires that raged across south-eastern Australia in 2019–20 led to a spike in atmospheric temperatures and probably made the hole in the ozone layer bigger, finds a study.
In the study, the researchers said that extreme drought in 2019 gave rise to bush fires of unprecedented intensity that burnt more than 5.8 million hectares. They said that the fires generated smoke that rose into the atmosphere and bumped up temperatures by 3 °C in the lower stratosphere over Australia. 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.
Scientific Reports published the study.
WILD FIRE; STARTOSPHERE
Stratosphere lies between roughly 10 and 50 kilometres above Earth’s surface. Generally, smoke particles do not get to the stratosphere. However, smoke from the Australian fires reached heights of more than 35 kilometres owing to unusual, fire-induced pyrocumulonimbus clouds. These smoke-infused thunderclouds hold lots of black carbon, which absorbs heat and rises into the lower stratosphere like a hot-air balloon, said study co-author Jim Haywood. He is an atmospheric scientist at the University of Exeter, UK .
Haywood and his team used data from polar-orbiting and remote-sensing satellites to observe changes in the distribution of smoke particles in the stratosphere. They combined the information with climate models. In the study, they found that the impact of smoke particles on stratospheric temperatures that was predicted by the models matched observed temperature spikes.
WILD FIRE; OZONE
The researchers said that the models also indicated that chemical reactions between 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.
Exactly how wild fire smoke and ozone interact is still a puzzle, owing to the complex chemical cocktail in smoke. Climate change is expected to increase the frequency and severity of wild fires, so Haywood emphasizes that it is important to nail down how smoke and fires will affect the ozone layer.
