The gradual recovery of the ozone layer over the Antarctic has apparently stopped the shift of the jet stream towards the South Pole. A research group led by Antara Banerjee from the University of Colorado at Boulder (Colorado, USA) reports in the journal “Nature” that this trend has stopped or even decreased slightly since 2000. The strong wind band had previously moved in the polar direction, which was also associated with climate changes in the southern hemisphere.
In the 1980s, scientists demonstrated that the ozone layer over Antarctica was thinning out. Since the ozone layer keeps part of the harmful ultraviolet radiation from the sun off the ground, the politicians of numerous countries acted quickly: In the Montreal Protocol of 1987, they banned chlorofluorocarbons (CFCs) and a number of other substances that have been shown to attack ozone in the high atmosphere. Since around 2000, researchers have observed that the ozone hole is gradually closing. If the current trend continues, the ozone hole over Antarctica will be history in 2050, the World Organization for Meteorology (WMO) reported in 2014.
Jetstream has an impact on many things
According to measurements, the summer jet streams around the Antarctic moved further south towards the end of the 20th century: from 49 degrees to 51 degrees south latitude. According to scientific evidence, this contributed to the warming of the Antarctic Peninsula, Patagonia (South America) and New Zealand. West Tasmania and West New Zealand also became drier. The jet streams also affected the circulation, temperature and salinity of the Southern Ocean. Researchers associate the shifting of jet streams with the ozone hole.
The researchers around Banerjee now wanted to know how the slow recovery of the ozone layer affects the jet stream and the climate of the southern hemisphere. “The challenge in this study was to prove our hypothesis that ozone layer recovery actually drives these atmospheric circulation changes and is not just a coincidence,” Banerjee said in a statement from her university. Because the climate around the South Pole is very variable, so that trends can only be made visible with sophisticated statistical methods.
The researchers used data from 1980 to 2017 and several, sometimes very different, climate models. Using numerous simulations, the researchers were able to show that the changes do not only have natural causes, such as volcanic eruptions or changes in solar radiation. Then they simulated individual possible causes for the change in the jet stream, such as greenhouse gases or the amount of ozone.
Slightly reversed trend recognizable
The Banerjee team found that the proportion of ozone in the upper atmosphere explains very well that the jet stream is no longer shifting further south, and that a slightly reversed trend is even discernible. The quantity of greenhouse gases causes the jet stream to shift towards the South Pole as a kind of opposite force. “It is the tug of war between the opposing effects of the ozone layer recovery and increasing greenhouse gases that will determine future trends,” Banerjee describes the current situation.
In a comment, also in “Nature”, writes Alexey Karpechko from the Finnish Meteorological Institute in Helsinki (Finland): “The results of the authors provide a clear signal that human actions can influence the earth’s climate: The Montreal Protocol has dealt with the ozone depletion associated climate change stopped. ” Limiting dangerous emissions and changing business practices is also the way to combat global warming caused by greenhouse gases, Karpechko emphasizes.