World Ozone Day: Emerging climate, space risks show fight to preserve ozone layer isn’t over

Even as the world gets set to eliminate ozone-depleting substances under the Montreal Protocol, climate change impacts and space advancement threaten the progress made so far
The Antarctic ozone hole, as recorded on September 14, 2024.
The Antarctic ozone hole, as recorded on September 14, 2024.
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In June this year, the world’s 35-year-long effort to restore and preserve its ozone layer got a major boost, when researchers confirmed dropping levels of chemicals which deplete this shield that protects us from the sun’s ultraviolet radiation. These chemicals, hydrochlorofluorocarbons (HCFC), are part of a set of 100-odd substances which have elements like chlorine and bromine that destroy ozone molecules.

Their release thus depletes the ozone layer 15 to 35 kilometres above the Earth’s surface. The ozone layer is the thinnest over the poles, especially in the Antarctic stratosphere, where the depletion is known as the “ozone hole”. But the June study, led by a scientist from Bristol University, UK and published in journal Nature Climate Change, indicated signs of ozone healing by noting that for the first time since the 1970s, the impact of HCFCs on the Earth’s energy balance and the amount of chlorine from these gases in the atmosphere have decreased after reaching a peak in 2021. This is five years ahead of the projected peak year of 2026.

More encouraging news came the same month, with a study led by researchers from the Indian Institute of Technology (IIT), Kharagpur, refuting claims made in 2022 of a “severe” ozone hole in the tropical stratosphere. Analysing ground-based and satellite data, the study said, “Current understanding and observational evidence do not provide any support for the possibility of an ozone hole occurring outside Antarctica today.”

The ozone layer is on track to recover because of successful implementation of the Montreal Protocol, a global agreement to phase out ozone-depleting substances like HCFCs, primarily used in air conditioning and refrigeration. Some 99 per cent of all ozone-depleting substances are already phased out, said the UN Environment Programme (UNEP), due to which the Antarctic ozone hole may also disappear by the 2060s. But sustaining this success may not be easy.

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The Antarctic ozone hole, as recorded on September 14, 2024.

Climate conundrum

The fight to preserve the ozone layer becomes more complex in a warming world. For instance, most sectors have replaced ozone-depleting HCFCs and chlorofluorocarbons with hydrofluorocarbons (HFC). HFCs do not threaten the ozone since they do not contain chlorine, but they have a high global warming potential.

Thus, with the 2016 Kigali Amendment, the Montreal Protocol sought to specifically phase out HFCs. UNEP is urging for greater action under the Kigali Amendment as part of its theme for World Ozone Day 2024 on September 16, Montreal Protocol: Advancing Climate Action. “If the Amendment is fully ratified and implemented, up to 0.5°C of warming could be avoided by 2100,” it said.

At the same time, climate change impacts may be threatening the stability of the ozone layer. In 2023, the Antarctic ozone hole emerged in August, rather than its usual time of September-October and persisted till late December, according to the Copernicus Atmosphere Monitoring Service (CAMS).

“It is the fourth year in a row that the Southern Hemisphere’s ozone hole showed peculiar behaviour,” said a December 21, 2023 article on CAMS’ website. Citing research studies, it suggested several reasons for this trend, including a volcanic eruption in Tonga in 2022, which injected into the stratosphere huge amounts of water vapour that can break down ozone through chemical reactions with chlorine molecules.

According to the United States space agency National Aeronautics and Space Administration or NASA, greenhouse gas emissions also have a cooling effect in the upper stratosphere, creating conditions that increase chlorine efficiency in ozone depletion.

A thin ozone layer also exposes the polar ecosystem and species to several types of ultraviolet rays, but much of these are absorbed by the ice sheets. But an April 2024 study led by a researcher from the University of Wollongong, Australia and published in journal Global Change Biology said climate change impacts in Antarctica such as shift in wind patterns and declining sea ice may increase organisms’ exposure to ultraviolet radiation.

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The Antarctic ozone hole, as recorded on September 14, 2024.

Another emerging risk is space activity. In June 2024, researchers from the University of Southern California, Los Angeles, US, published a study warning that satellites may harm the ozone layer. “Satellites burn up at the end of service life during reentry, generating aluminum oxides as the main byproduct. These are known catalysts for chlorine activation that depletes ozone in the stratosphere,” said their study, published in Geophysical Research Letters.

The study noted that a “mega-constellation” of satellites could release 360 tonnes of aluminium oxides per year, leading to significant ozone depletion.

In a June 24 New York Times article on the study, David Fahey, a co-chair of the Scientific Assessment Panel of the Montreal Protocol, was cited saying, “This is something the world should really take seriously, and the Montreal Protocol is aware and will be studying this.” In the article Fahey, who is also director of the Chemical Sciences Laboratory at the US National Oceanic and Atmospheric Administration (NOAA), said the subject would be explored in the next assessment of the Montreal Protocol in 2026.

In July, a UNEP report, Navigating New Horizons—A Global Foresight Report on Planetary Health and Human Wellbeing, also noted that increase in space activity can release gases and compounds that deplete the ozone layer. With the global space industry projected to grow to $3.7 trillion by 2040, monitoring  is needed to ensure that the progress made to protect the ozone layer through the Montreal Protocol is not undone, said the report.

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