After the discovery of the stratospheric ozone hole over Antarctica, scientists across the world raised concerns over its catastrophic impacts and called world leaders to deliberate and take measures to save the ozone layer. The Montreal Protocol of 1987 was the outcome of these continuous deliberations and provided direction to phase down the consumption and production of the different ozone depleting substances (ODSs). Scientists have revealed that this collaborative protocol has yielded positive results in the form of pausing and even reversing southward shifting of jet streams (strong air currents around the Southern Hemisphere), driven by ozone depletion in the Antarctic stratosphere.
This pause or even reversal to some extent is not only linked to internal or natural variability, but human activities. A study by a group of scientists, published in the journal Nature, concluded that stratospheric ozone recovery is the key driver of the pause. “It is 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, from the National Oceanic and Atmospheric Administration (NOAA).
Before this study, in September 2019, satellite images had revealed that the ozone hole annual peak had shrunk to 16.4m sq km, the smallest extent since 1982. The NASA and NOAA satellite measurements had noted that the annual ozone hole reached its peak extent on September 8, 2019 and then shrank to less than 10 million sq km for the remainder of September and October. And now, this has been confirmed by the new study with impactful evidence.
Ozone depletion over Antarctica was found to be the prime culprit for the southward shifting of the westerly jet stream which consequently affected the weather and the climate. A study by Sukyoung Lee and Steven Feldstein at Pennsylvania State University in University Park in 2013 had observed that ozone loss contributed about 50 per cent more than greenhouse gases towards the jet-stream changes. That particular study had also revealed that alterations in the powerful southern jet stream, particularly in summer, were linked to the variations in rain patterns and storm locations in the southern hemisphere. In Australia shifting of the jet stream had increased the risk of droughts by pushing rain away from coastal areas. But now, with the shrinking in the ozone hole, the weather pattern is bound to reverse again.
Reversal in the jet stream, however, is not going to yield the same outcome for all the affected regions. For example, Patagonia in Chile and Argentina, and regions suffering from droughts in Australia will receive more rains, while it will bring some drought concerns for central South American countries such as Uruguay, Paraguay, and Southern Brazil as ozone depletion was previously found to bring in more rains.
Second, restoring the ozone layer alone is not going to reverse the weather pattern as carbon dioxide and methane emissions from industrial and agriculture activities continue to grow.
Arctic Ozone hole at record level
While the ozone hole over Antarctica is shrinking, scientists in contrast have recorded the largest hole in the ozone layer over the Arctic. Ozone holes over the Arctic, a rarer one, is the result of persistent cold temperatures in the polar region and unusually quiet ozone dynamics, said Paul Newman, chief scientist for earth sciences at NASA’s Goddard Space Flight Center. These persistent cold temperatures caused formation of polar stratospheric clouds, which play a key role in the destruction of ozone.
Ozone is a highly reactive molecule of three oxygen atoms that origins naturally in small amounts. The ozone layer is located in the earth’s stratosphere from 10 to 50 km above the surface. The layer shields the planet from potentially harmful ultraviolet radiation that can cause skin cancer and cataracts, suppress immune systems and damage vegetation. Antarctic ozone slowly decreased in the 1970s, and researchers at the British Antarctic Survey discovered the ozone hole in 1985.
The Montreal Protocol, 1987
Adopted on 15 September 1987, the Montreal Protocol on Substances that Deplete the Ozone Layer regulates the production and consumption of nearly 100 man-made chemicals referred to as ozone depleting substances (ODS). The Protocol is to date the only United Nations (UN) treaty ever that has been ratified by every country–all 197 UN member states. The substances controlled by the treaty are listed in Annexes A (CFCs, halons), B (other fully halogenated CFCs, carbon tetrachloride, methyl chloroform), C (HCFCs), E (methyl bromide) and F (HFCs). The Protocol was amended and adjusted in 1990, 1992, 1997 and 1999. Later, Kigali Amendment of 2016 extended controls to phase down the production and consumption of hydrofluorocarbons (HFC).
Banerjee, A., Fyfe, J.C., Polvani, L.M. et al. A pause in Southern Hemisphere circulation trends due to the Montreal Protocol. Nature 579, 544–548 (2020). https://doi.org/10.1038/s41586-020-2120-4
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Jet-stream shifts linked to ozone. Nature 494, 8 (2013). Available at https://doi.org/10.1038/494008d
NASA-2019 Ozone Hole is the Smallest on Record Since Its Discovery.
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Watts, J. Global efforts on ozone help reverse southern jet stream damage. The Guardian, available at https://bit.ly/34fxbqd