Study Shows Global Concerted Efforts Help Restore Southern Jet Stream To Its Normal State

Global efforts on ozone-depleting chemicals help reverse southern jet stream damage and jet stream appears to have stopped moving south and maybe moving back towards normal state after decades of disruption caused by humans, a study shows.

The findings prove that there is the capacity to heal damaged climate systems, scientists say, only if governments act on time and deal with the causes with coordination.

The southern jet stream is a powerful wind that, particularly in the summer, shapes weather patterns and ocean currents in the southern hemisphere.

It had been shifting from its typical course until 2000 and each decade, moving southwards towards the Antarctic at a rate of one degree of latitude affecting storm tracks and rainfall over South America, East Africa, and Australia.

According to the previous research, this was primarily due to the depletion of the ozone layer by human-made chemical compounds like chlorofluorocarbons, hydrochlorofluorocarbons, found in fridges, aerosols, and other industrial processes.

These chemicals were used in vast quantities and thinned the ozone layer resulting in a widening “hole” high above the South Pole, affecting the patterns of wind. Then under the United Nations 1987 Montreal protocol, they started to be phased out.

The new paper, published in the journal Nature, shows that the Montreal protocol has stopped the jet stream moving southward since the turn of the century and as the ozone hole begins to close, it may even be starting to reverse. The annual peak of the ozone hole had shrunk to 16.4m sq km, the smallest extent since 1982, satellite images revealed last September.

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“It’s a success story. This is more evidence that the Montreal Protocol has led to the recovery of the ozone layer,” said the study’s lead author, Antara Banerjee, who works in the chemical sciences division of the National Oceanic and Atmospheric Administration and is a visiting fellow at the University of Boulder, Colorado.

The anticipated impact on people will vary from region to region. In Patagonia (southern Chile and Argentina), rain should be more and carcinogenic ultra-violet light will be less. However, for central South America, the findings will be of more concern (Uruguay, Paraguay, southern Brazil, and northern Argentina), where ozone depletion was earlier found to bring more rainfall and broader bands of agricultural production. A similar effect will likely be seen in east Africa and other desert areas in the mid-latitudes.

The reversal may bring good news for Australia, which has faced more droughts because, during winter, the movement of the jet stream pushed rain-bearing storms away from its coast, previous studies suggest. But, whether this is enough to offset the rise in carbon emissions is a different matter.

Only restoration of ozone is not enough to push southern hemisphere weather patterns back on to a regular track as other industrial emissions like carbon dioxide and methane continue to exert a disruptive force in the opposite direction.

“There is a tug of war between ozone recovery and increasing CO2. That’s why we are seeing a pause. In the near future, the ozone factor could dominate and the jet stream will move back towards equator. But once the recovery is complete, CO2 could push it southwards again,” Banerjee said.

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According to Alexey Karpechko, a reviewer of the paper who works for the Finnish Meteorological Institute, the paper showed how ozone depletion had impacted atmospheric circulation significantly.

“This is good news, definitely. It shows our actions can stop climate change,” he said. “We can see coordinated action works. It is a strong message to us as emitters of greenhouse gases. This shows we can manipulate the climate both ways: in a wrong way and by reversing the damage we have done.”

However, whether this will affect the loss of Antarctic sea ice remains unanswered. Previous studies suggested the ozone hole had a chimney-like effect that sucked some of the heat out of the atmosphere for which the South Pole warmed more slowly than the north. But as per Banerjee, such a view was controversial and required further study.

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