Positive omen for the ozone layer over the Arctic

September 26 () –

Ozone concentrations over the Arctic reached a record average at the end of last winter, which should be considered a positive omen for the ozone layer in the region.

Due to large-scale weather systems that disrupted the upper atmosphere during the winter of 2023–2024, more ozone migrated into and persisted in the stratosphere over the Arctic than at any other time in the satellite record.

A team of scientists from NASA and the University of Leeds reported their findings in a September 2024 paper in Geophysical Research Letters. “Given the absence of high Arctic ozone since the 1970s,” the authors wrote, “the March 2024 record “should be seen as a positive omen for future Arctic ozone layer depletion.”

Between December 2023 and March 2024, a series of planetary-scale waves propagated upward through the atmosphere and slowed the stratospheric jet stream circulating around the Arctic. When that happens, mid-latitude air converges at the pole, sending ozone into the Arctic stratosphere. Other than the influx of ozone, there was very little of the typical ozone depletion from substances like chlorine, said Paul Newman, chief scientist for Earth sciences at NASA’s Goddard Space Flight Center and lead author of the study. “It was a very dynamic and active winter in the Northern Hemisphere,” he said. in a statement.

LOWER ULTRAVIOLET RADIATION IN THE NORTHERN HEMISPHERE

More stratospheric ozone is good for life on Earth. The stratospheric ozone layer is a natural sunscreen that absorbs harmful ultraviolet (UV) radiation. The authors calculated that, from April to July 2024the UV index was between 6 and 7 percent lower in the Arctic and 2 to 6 percent lower in the mid-latitudes of the Northern HemisphereLess UV radiation means less damage to plant DNA and a lower risk of cataracts, skin cancer and suppressed immune systems in humans and animals.

Activity in March 2024 contrasts sharply with March 2020, when stratospheric ozone concentrations reached extremely low levels. Uninterrupted by upper atmospheric wave events, sustained circumpolar winds prevented ozone from other latitudes from replenishing the Arctic stratosphere. The stable polar vortex also created cooler-than-average conditions favorable for ozone-depleting reactions to occur.

Unlike Antarctica, where ozone holes form every year, the concentration of ozone over the Arctic is highly variable and is subject to the “annual whims” of the tropospheric and stratospheric climate, said Newman.

Strong wave events from late December 2023 to early March 2024 resulted in the increases in ozone concentrations seen in the graph above. Ozone levels peaked in March, as is typically the case, and then remained well above average. May, June, July, and August also set new records for monthly average ozone concentrations. “It really is an extraordinary northern summer period,” said Newman.

As for what might have caused the unusual stratospheric weather, the authors looked at a variety of factors. without finding a clear answer. The effect of climate change, for example, is difficult to quantify. “There may be a climate factor here, but it’s not obvious,” Newman said. Regarding broader atmospheric patterns, such as El Niño and the Quasi-Biennial Oscillation: “Possibly, but the contribution is relatively small.”

In addition to stratospheric weather, which is the main driver of Arctic ozone levels, the authors believe that long-term trends likely drove ozone concentrations to record highs. Since the Montreal Protocol phased out production of ozone-depleting chlorofluorocarbons (CFCs) and halons in 1987, ozone levels have been slowly recovering.

The high levels in March 2024 were therefore within the authors’ expectations: Goddard’s chemical-climate model, GEOSCCM, showed a 1 in 8 chance of a record high by 2025, with more records predicted in the future. However, because CFCs persist in the atmosphere for decades, Average Arctic ozone is not expected to return to 1980 levels until about 2045they point out.

Higher concentrations of greenhouse gases in the stratosphere also accelerate ozone recovery. “This record was likely a result of the decrease in ozone-depleting substances and the increase in greenhouse gases. Otherwise, it would have just been a high year and not a record,” Newman said. “I call this year a harbinger of things to come.”