Negative feedback loops: Bushfires and the ozone layer

On the role between increased rates of Australian bushfires, released aerosols and rapid ozone depletion.

The story of the ozone layer’s destruction is drilled into the memory of every Australian school kid. It was one of the first examples of historical environmental destruction we were exposed to. 

Unfortunately, ozone depletion has been spotlighted once more following the Black Summer bushfires. Research conducted at the University of Waterloo found that aerosols from the fires are contributing to a decline in atmospheric ozone.

How are historical and contemporary ozone depletion related?

Ozone is a gas comprising three oxygen atoms and residing in the Earth’s upper atmosphere. The gas is highly reactive and prone to turning into regular oxygen gas when exposed to the right chemicals in the right environment. Historically-emitted CFCs — which will remain in the atmosphere for decades to come — release highly-reactive ‘chlorine free radicals’ when exposed to UV light from the Sun. Just one of these chlorine species can destroy over 100,000 molecules of ozone before it eventually leaves the ozone layer. 

The ozone hole looms over Antarctica because its atmospheric conditions are ripe for the production of ozone-destroying particles. Less reactive gases accumulate near the South Pole in the winter. When summer arrives, ice crystals and water droplets suspended in the clouds convert them to more reactive species, like chlorine radicals. 

Additionally, the increased global temperature and melting polar caps have led to a longer period for ozone to react with these radicals.

While the hole does not extend past Antarctica, the surrounding parts of the ozone layer have been thinned, leaving Australia and Oceania less protected from the Sun.

The aerosols pumped in the atmosphere during the 2019-2020 Black Summer bushfires are enabling a similar process to take place outside the confines of the Antarctic region. Much like the atmospheric ice crystals, ash particulates provide a surface for reactive species to form, including chlorine nitrate, hypochlorous acid, and chlorine monoxide. Concerningly, this may slow the recovery of the ozone layer.

A delayed recovery creates a negative feedback loop. Scientists have predicted a “likely understated” estimate of 30 per cent increase in bushfire frequency if ozone depletion continues at its current rate. More severe fires lead to more aerosols, which further slows ozone recovery, which will increase bushfire frequency. As we saw with the Black Summer bushfires, the consequences were disastrous for wildlife and our agricultural industries..

A depleted ozone layer also means greater UV exposure which has consequences for human and nonhuman species alike. Skin cancer is strongly correlated with UV exposure. UV rays also harm marine habitats like the Great Barrier Reef, and force sealife to migrate deeper into the ocean to avoid the rays. 

Any process that will exacerbate the depletion of our ozone layer should warrant an immediate response.

When CFCs were discovered to be responsible for ozone depletion in 1974, there was a rapid multilateral agreement to halt CFC production. The Montreal Protocol of 1987 brought over 200 countries together to replace CFCs with the assumed-safer HFCs. While better than CFCs they are greenhouse gases and the 2016 Kigali Amendment is a step towards mitigating their use too.

Now that climate change-exacerbated bushfires have been identified as a new source of ozone depletion, a similar rapid multilateral approach is required. Addressing ozone depletion is no longer a simple matter of banning the production of a single molecule: it requires immediate substantive action on climate change, including better adaptation strategies to longer and more severe bushfire seasons. In solving this problem, we might just save the planet too.