It protects the Earth from dangerous solar radiation. The ozone layer is nevertheless mistreated by chemical substances which enlarge its hole each austral spring, according to a study published Tuesday. The stratospheric ozone layer, located between 11 and 40 kilometers above the earth’s surface, filters the sun’s ultraviolet rays which can cause cancer, alter the immune system and even damage the DNA of living beings.
In the mid-1970s, chlorofluorocarbons (CFCs), once widely used in aerosols and refrigerators, were identified as the main culprit in thinning the ozone layer, creating “holes” each year, including one particularly wide above Antarctica.
A reduction of the hole which takes time
The 1987 Montreal Protocol, which banned CFCs to close these gaps, is considered a success story in global environmental cooperation. Last January, experts commissioned by the UN judged the agreement effective: according to their forecasts, the ozone layer should recover by around 2066 above Antarctica, 2045 above Arctic and 2040 in the rest of the world. But despite the decline in CFCs, the hole over Antarctica has not yet been significantly reduced, according to the authors of a study published in Nature Communications.
“Six of the last nine years have seen very low ozone levels and extremely large ozone holes,” Annika Seppala, from the physics department at New Zealand’s University of Otago, told AFP. , co-author of the study. “It could be that something else is happening in the atmosphere – perhaps because of climate change – and masking some of the recovery,” she added.
A later opening
The hole in the ozone layer over Antarctica usually opens in September and lasts until November, during the austral spring, before gradually filling up. According to the researchers, the hole opened later in September, a sign of a recovery undoubtedly attributable to the reduction of CFCs.
But in October, the period when the hole reaches its maximum size, the level of ozone in the middle stratospheric layer fell by 26% between 2004 and 2022, according to their work which is based on satellite data. The reduction in CFCs in the atmosphere decided by the Montreal Protocol nevertheless remains “on track”, underlines Hannah Kessenich, the main author. But “our conclusions reveal that these large holes, formed recently, would not be solely caused” by these substances.