Global Ban on Ozone-Eating Chemicals Credited in Change to Southern Jet Stream

(CN) – International efforts to curb ozone-depleting chemicals have paused and potentially reversed shifting jet stream winds that affect storm patterns, ocean temperatures and Antarctic sea ice in the Southern Hemisphere, scientists found in a study released Wednesday.

Signed by 197 nations, the Montreal Protocol of 1987 became the first United Nations treaty to achieve universal ratification. The landmark agreement phased out the production and use of chlorofluorocarbons (CFCs), widely used chemicals that were found in 1985 to be causing a hole in the ozone layer which protects the Earth from harmful ultraviolet radiation.

The European Union’s Sentinel-3B satellite captured this picture of sunset over the Weddell Sea off the coast of Antarctica this month, less than two weeks after its launch. (European Space Agency)

According to the study in the journal Nature, the decline in ozone-depleting chemicals has not only helped repair a hole in the planet’s critical ozone layer. It has also halted changes to the Southern Hemisphere’s mid-latitude jet stream.

“Our study is showing how profound an impact the Montreal Protocol has had on the Earth’s system,” said Antara Banerjee, co-author of the study. “It was meant to be just a treaty to protect the ozone layer but it’s actually having very profound effects on the climate all the way down to the earth’s surface.”

Banerjee is a postdoctoral associate at the Cooperative Institute for Research in Environmental Sciences, a partnership of the University of Colorado, Boulder and the National Oceanic and Atmospheric Administration.

By reviewing observational data from the late-1970s onward, Banerjee and her colleagues found ozone depletion caused the Southern Hemisphere’s mid-altitude jet stream to move toward the Earth’s southern pole. The poleward shift caused major changes to the atmosphere, affecting air and ocean temperatures, precipitation, Antarctic ice cover and ocean salinity.

The changes were noticed starkly in Australia, where storms have become more frequent in some regions and less frequent in others, according to the study’s co-author Joh Fyfe, senior research scientist with Environment & Climate Change Canada.

The shifting winds and weather patterns affect each region differently, Banerjee explained.

“Continents such as east Africa, it has been suggested there’s been warming there,” Banerjee said. “Some regions are getting wetter. Some are getting drying. Some are getting warmer, and some are getting cooler.”

Observational evidence confirmed the jet stream stopped shifting toward the South Pole in the early 2000s after most ozone-depleting chemicals were banned. From there, Banerjee and her colleagues used a technique called Detection and Attribution analysis to find out what caused the poleward shift to stop.

Using sophisticated computer models, the scientists ran simulations to determine if random fluctuations, rather than human activity, caused the change. Those models confirmed the hypothesis that a reduction in ozone depleting chemicals was the catalyst.

According to Banerjee, model simulations have long predicted that ozone recovery would pause or reverse the shifting jet stream winds, but this study confirmed that theory.

“It’s really exciting to be able to see that in real world observations,” Banerjee said. “It’s a validation of our climate models and a validation of our theoretical understanding and also of the scientific method.”

However, the scientists warn that the change is not irreversible. The growing influence of carbon emissions could cause the jet stream to start moving poleward again. The effect of increasing carbon dioxide and ozone recovery “balanced each other” in a way that made the jet stream stay approximately constant, Banerjee explained. She described it as a kind of “tug of war” between the two effects.

“Unless future CO2 emissions are mitigated, the jet stream will start to move poleward again,” she said.

Banerjee’s co-author Fyfe explained that once the hole in the ozone layer is repaired, the “greenhouse gas effect will become more apparent.”

The findings have encouraged Fyfe and his team to investigate how this pause in the jet stream’s shift has affected a plethora of atmospheric conditions, including ocean and air temperatures, ocean salinity, Antarctic sea ice, in a future study.

Fyfe added that this study also signals hope that when needed, the nations of the world can work together to solve the planet’s biggest problems and change the world for the better.

“The destruction of the ozone was a problem that seemed to be not solvable, but the countries of the world got together, hammered out a deal, stopped emitting CFCs and here’s the positive outcome,” Fyfe said.

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