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EXPERT REACTION: Cutting ozone killers has changed our southern hemisphere jet streams

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The recovery of the ozone layer and the shrinking of the ozone hole have paused a shift in southern hemisphere jet streams, which were affecting rainfall and ocean salinity, according to US, Canadian and Aussie authors. Prior to 2000, the ozone depletion was driving changes in the Southern Hemisphere circulation which were then changing rainfall patterns. The team say that this altered circulation paused around the year 2000, likely due to the Protocol. However, the team warns that as carbon dioxide emissions continue to rise, it is unclear whether the pause in atmospheric circulation trends will continue.

Journal/conference: Nature

DOI: 10.1038/s41586-020-2120-4

Organisation/s: The University of New South Wales, National Oceanic and Atmospheric Administration/Earth System Research Laboratory, Boulder, CO, USA

Funder: This work was funded by grants from the US National Science Foundation (NSF) to Columbia University and a fellowship from the Cooperative Institute for Research in Environmental Sciences (CIRES).

Media Release

From: Springer Nature

Changes in Southern Hemisphere circulation 

Changes in atmospheric circulation linked to the recovery of the ozone layer in the Southern Hemisphere are reported in a paper in Nature. The research into these changes suggests that this effect is a direct result of the implementation of the Montreal Protocol. 
Human-generated emissions of ozone-depleting substances have contributed to a decline in ozone, which has caused changes in atmospheric circulation in the Southern Hemisphere. The main effects include a poleward shift of the mid-latitude jet stream and the expansion of both tropical circulation and the subtropical dry zone. These changes have been shown to have impacted precipitation and have potentially affected ocean circulation and salinity in the Southern Hemisphere. 
Antara Banerjee and colleagues use 1980–2017 atmospheric reanalyses ― a combination of data and modelling ― to show that these trends have paused or reversed since around the year 2000. For example, they found that the Southern Hemisphere jet stream moved poleward until 2000, when it seemed to pause. This timing coincides with Antarctic ozone recovery around the year 2000 and suggests that the decline in ozone-depleting substances, as mandated by the Montreal Protocol, may be responsible for the pause in circulation trends. 
These findings indicate that the Montreal Protocol may have also affected other aspects of the Earth system, although the authors note that as carbon dioxide emissions continue to rise, it is unclear whether the pause in atmospheric circulation trends will continue

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Expert Reaction

These comments have been collated by the Science Media Centre to provide a variety of expert perspectives on this issue. Feel free to use these quotes in your stories. Views expressed are the personal opinions of the experts named. They do not represent the views of the SMC or any other organisation unless specifically stated.

Professor Ian Rae is an expert on chemicals in the environment at the School of Chemistry at the University of Melbourne. He is also an advisor to the United Nations Environment Programme on chemicals in the environment and is former President of the Royal Australian Chemical Institute.

Depletion of the stratospheric ozone layer has always been presented to us under two headings: we have caused the problem by using industrial chemicals that leak into the atmosphere; and less ozone means we are exposed to more of the harmful UV radiation.

But there's more. Atmospheric scientists know that there is a connection between what's going on in the ozone layer and the way air moves from west to east around the southern hemisphere. If you have had a fast trip home from Perth, you would know about the jet stream. And we know that Melbourne's weather, especially our rain, mostly comes from the west and south-west. The 'weather bands' that bring our cold fronts have been narrowing towards the south pole, and that's why southern Australia has experienced decreasing rainfall over the last thirty years or so. If the ozone layer is recovering, and the circulation is moving north, that's good news on two fronts (pun not intended).

Last updated: 25 Mar 2020 12:38pm
Declared conflicts of interest:
None declared.

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