It’s been more than 30 years since the world banned the chemicals that break down the Earth’s protective ozone layer, while at the same time triggering some disturbing changes in atmospheric circulation in the southern hemisphere.
Now, new research is published in this week nature notes that these changes have been suspended and may even reverse due to the Montreal Protocol – an international treaty that successfully ended the use of chemicals to deplete the ozone layer.
“This study contributes to the growing evidence that demonstrates the profound effectiveness of the Montreal Protocol. The contract has not only advanced healing of the ozone layer, but also promoted the recent changes in air circulation patterns in the southern hemisphere, ”said lead author Antara Banerjee, a CIRES visiting scientist at the University of Colorado Boulder, who works in the Department of Chemical Sciences at the National Oceanic and Atmospheric Administration (NOAA).
The ozone hole discovered in 1
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Previous studies have linked these circulation trends to weather changes in the southern hemisphere, particularly rainfall over South America, East Africa and Australia, as well as changes in ocean currents and salinity.
With the Montreal Protocol of 1987, the production of ozone-depleting substances such as chlorofluorocarbons (CFCs) was discontinued. From about 2000 the concentrations of these chemicals in the stratosphere began to decrease and the ozone hole began to recover. In this study, Banerjee and her co-authors showed that around 2000 the circulation of the southern hemisphere also stopped the expansion of the Polewards – a pause or a slight reversal of previous trends.
“The challenge in this study was to prove our hypothesis that ozone recovery is actually driving these atmospheric circulation changes, and it’s not just a coincidence,” said Banerjee.
To this end, the researchers used a two-step statistical technique called detection and attribution: they recognized whether certain patterns of observed wind changes were unlikely to be due to natural variability alone, and if so, whether the changes were man-made Changes are attributable to factors such as emissions of ozone-depleting chemicals and CO2.
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Using computer simulations, the researchers initially found that the observed pause in circulation trends cannot be explained by natural wind shifts alone. Next, they isolated the effects of ozone and greenhouse gases separately.
They showed that while rising CO2 emissions continued to increase near-surface circulation (including the jet stream), only the changes in ozone could explain the pause in circulation trends. Before 2000, both ozone depletion and rising CO2 values drove the near-surface cycle towards the pole. CO2 has been driving this cycle forward since 2000 and offsets the opposite effect of ozone recovery.
“Detecting the ozone-related pause in circulation trends in real observations confirms for the first time what the scientific ozone community has long predicted from theory,” said John Fyfe, a scientist at Environment and Climate Change Canada and one of the scientists’ co-authors of the paper.
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As ozone recovery and CO2 levels continue to rise, the future is less certain, also for the regions of the southern hemisphere, whose weather is affected by the jet stream, and the regions on the edge of the arid regions.
“We call this a” pause “because the Poleward circulation trends may resume, stay flat, or reverse,” Banerjee said. “It is the tug of war between the opposing effects of ozone recovery and rising greenhouse gases that will determine future trends.”
However, a 2018 United Nations report states that the notorious hole in the ozone layer could be completely healed by 2060 – and in some regions of the world, it could be as early as 2030.
Reprinted from the Cooperative Institute for Environmental Research
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