Australia’s ‘Black Summer’ wildfire widened ozone hole by 10% in 2020, study finds

Fires may have led to a 3 to 5 per cent depletion of ozone in regions overlying Australia, New Zealand, and Africa

Australia’s Black Summer wildfires in 2020 widened the ozone hole by 10 per cent, according to a new study that warns that smoke particles from such fires can erode the Earth’s protective layer shielding it from the sun’s ultraviolet radiation.

The research, published last week in the journal Nature, assessed the impact of smoke from the “Black Summer” mega wildfire in eastern Australia that burned from December 2019 into January 2020, directly killing 36 people and harming over three billion animals.

The megafire, which is Australia’s most devastating on record, scorched tens of millions of acres and pumped over a million tons of smoke into the atmosphere, say researchers, including those from Massachusetts Institute of Technology in the US.

Scientists identified a new chemical reaction by which smoke particles from the Australian wildfires made the ozone depletion worse.

They say the fires may have led to a 3 to 5 per cent depletion of total ozone in regions overlying Australia, New Zealand, and parts of Africa and South America by triggering this chemical reaction.

The study suggests the fires may have also eaten away at the edges of the ozone hole over Antarctica by late 2020, widening it by 2.5 million square kilometres, or about 10 per cent of its area compared to the previous year.

While the United Nations recently noted that ozone depletion around the world is on a recovery track due to international efforts to phase out chemicals depleting the Earth’s protective layer, scientists say the long-term effect of wildfires on its recovery remain unclear.

Previous research had found that chlorine-containing compounds such as those emitted by factories could react with the surface of fire aerosols and set off a cascade of chemical reactions producing chlorine monoxide – the ultimate ozone-depleting molecule.

The new study found that the Australian wildfires likely depleted ozone via this chemical reaction.

As long as chemicals from such mega wildfires persist in the atmosphere, researchers say they could trigger a reaction that temporarily depletes the ozone layer.

“The effect of wildfires was not previously accounted for in [projections of] ozone recovery. And I think that effect may depend on whether fires become more frequent and intense as the planet warms,” study co-author Susan Solomon from MIT said.

Researchers also found that some of the chlorine-related chemistry they discovered in the atmosphere could not explain all the changes they found in the Earth’s upper atmosphere.

When scientists analysed the composition of molecules in the stratosphere following the Australian wildfires using satellite data, they found elevated levels of chlorine monoxide and a drop in hydrochloric acid concentrations.

Studies have shown that when chlorine is bound in the form of HCl, it doesn’t destroy ozone, but when the acid molecules break apart, the chlorine can react with oxygen to form the ozone-depleting chlorine monoxide.

“The fact that HCl at mid-latitudes dropped by this unprecedented amount was to me kind of a danger signal,” Dr Solomon explained.

“There’s now sort of a race against time. Hopefully, chlorine-containing compounds will have been destroyed, before the frequency of fires increases with climate change. This is all the more reason to be vigilant about global warming and these chlorine-containing compounds,” she added.