While previous work has shown that the ozone hole is changing atmospheric flow at high latitudes, a Science paper by researchers from Columbia University, US, demonstrates that the ozone hole is able to influence tropical circulation and increase rainfall at low latitudes in the entire Southern Hemisphere. This is the first time that ozone depletion – an upper atmospheric phenomenon confined to the polar regions – has been linked to climate change from the Pole to the equator.
"The ozone hole is not even mentioned in the summary for policymakers issued with the last IPCC report," says Lorenzo Polvani, co-author of the paper. "We show in this study that it has large and far-reaching impacts. The ozone hole is a big player in the climate system."
Lead author Sarah Kang says: "It's really amazing that the ozone hole, located so high up in the atmosphere over Antarctica, can have an impact all the way to the tropics and affect rainfall there – it's just like a domino effect."
The ozone hole is now widely believed to have been the dominant agent of atmospheric circulation changes in the Southern Hemisphere in the last half century. This means, according to Polvani and Kang, that international agreements about mitigating climate change cannot be confined to dealing with carbon alone – ozone needs to be considered, too. "This could be a real game-changer," says Polvani.
Over the past decade ozone depletion has largely halted. Scientists now expect it to fully reverse, with the ozone hole closing by mid-century.
"While the ozone hole has been considered as a solved problem, we're now finding it has caused a great deal of the climate change that's been observed," says Polvani.
Together with colleagues at the Canadian Centre for Climate Modelling and Analysis, Kang and Polvani used two different state-of-the-art climate models to show the ozone hole effect. They first calculated the atmospheric changes in the models produced by creating an ozone hole. They then compared these changes with the ones that have been observed in the last few decades: the close agreement between the models and the observations shows that ozone is likely to have been responsible for the observed changes in the Southern Hemisphere.
Kang and Polvani plan next to study extreme precipitation events, which are associated with major floods, mudslides, etc. "We really want to know," says Kang, "if and how the closing of the ozone hole will affect these."