International Ozone Pact Pauses Changes In Southern Hemisphere Winds

Katie Ramirez
March 28, 2020

The authors of the study noted that stopping ozone depletion may have paused or even reversed the harmful changes in the Southern Hemisphere's air currents. The Montreal Protocol identified these substances as the main culprit in the depletion of the ozone layer.

A year ago the Antarctic ozone hole hit its smallest annual peak on the document - because it was found in 1982 - nevertheless, it's a temporary fix. Now, new research in Nature finds that those changes have paused and might even be reversing because of the Montreal Protocol, an global treaty that successfully phased out use of ozone-depleting chemicals. Ultimately, ozone depletion has shifted the midlatitude jet stream and the dry regions at the edge of the tropics toward the South Pole. As this belt got wider, the number of storms and the amount of rainfall in South America, East Africa and Australia was changing.

Since 2000, trends have shown recovery and in 2019 the ozone hole was the smallest it has been since it was discovered.

The challenge in this study was proving our hypothesis that ozone recovery is in fact driving these atmospheric circulation changes and it isn't just a coincidence.

Researchers used a range of computer simulations to show the jet stream stopped moving south at the same time as the ozone hole began healing. This study was started while she was a Postdoctoral Fellow at Columbia University.

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The researchers achieved this by employing a two-step statistical method known as detection and attribution: detecting whether specific patterns of wind changes noticed are unlikely to be caused by natural variability alone and, if so, whether the variations could be due to human-induced factors, like emissions of ozone-depleting chemicals and CO2.

For example, the lowering of the jet stream increased the risk of droughts throughout Australia, but if the ozone layer fully recovers, which, it is important to add, has not yet, then the rains over Australia could return. Scientists say this can be on account of unusually gentle temperatures in that layer of the ambiance. "That might change in the future when ozone has fully recovered and Carbon dioxide carries on pushing it south".

"We term this a "pause" because the poleward circulation trends might resume, stay flat, or reverse," says atmospheric chemist Antara Banerjee from the University of Colorado Boulder.

The Montreal Protocol has proven to be a crucial step in helping to pause or even compensate for the damage caused by humanity globally, but despite this, the steady increase in greenhouse gas emissions shows that we need to do much more than that.

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