From NASA’s Earth Observatory:
Ozone concentrations in the Arctic reached a record monthly average in March 2024. Due to large-scale weather systems disrupting the upper atmosphere during the winter of 2023-2024, more ozone moved into and remained in the stratosphere in the Arctic than anything else. other times in satellite recordings.
A team of scientists from NASA and the University of Leeds reported their findings in a September 2024 paper on Geophysical Research Letters. “Since there has been no Arctic ozone high since the 1970s,” the authors wrote, “the record high in March 2024 should be considered a positive sign of the Arctic ozone layer in the future.”
Between December 2023 and March 2024, a series of planetary-scale waves propagated upward in the atmosphere and accelerated the stratospheric jet stream surrounding the Arctic. When this happens, air from the mid-latitudes gathers at the poles, sending ozone into the Arctic stratosphere. In addition to ozone depletion, there is very little ozone depletion typical of substances such as chlorine, said Paul Newman, chief earth science scientist at NASA’s Goddard Space Flight Center and lead author of the study. “This is a dynamic and active winter in the northern hemisphere,” he said.
Stratospheric ozone is more positive for life on Earth. The stratospheric ozone layer is a natural sunscreen, absorbing harmful ultraviolet (UV) radiation. The authors calculate that from April-July 2024, the UV index will be 6 to 7 percent lower in the Arctic and 2 to 6 percent lower in the northern hemisphere. Less UV radiation means less plant DNA damage and a lower risk of cataracts, skin cancer, and suppressed immune systems in humans and animals.
Activity in March 2024 is in stark contrast to March 2020, when stratospheric ozone concentrations reached very low levels. Without interference from upper atmospheric wave events, the steady circumpolar winds prevent ozone from other latitudes from replenishing the Arctic stratosphere. The stable polar vortex also creates colder-than-average conditions, which are ideal for ozone-depleting reactions.
The map above shows ozone concentrations in the Arctic for March 2020 (left) and March 2024 (right), illustrating the many variations that can occur there. The monthly average is calculated by the NASA Ozone Watch team and is based on data obtained by OMPS (Ozone Mapping Profiler Suite) on the NASA-NOAA Suomi-NPP satellite.
Unlike in Antarctica, where ozone holes form every year, ozone concentrations in the Arctic are highly variable and subject to “year-to-year variations” in tropospheric and stratospheric weather, Newman said.
1979 – 2024
A strong wave event from late December 2023 to early March 2024 caused ozone concentrations to increase in the graph above. Ozone levels peaked in March, as usual, and then remained above average. May, June, July, and August also set new records for monthly average ozone concentrations. “It really is an incredible northern summer period,” Newman said.
As for what could cause the unusual stratospheric weather, the authors looked at various factors without finding a clear answer. The effects of climate change, for example, are difficult to measure. “There may be a climatic factor here, but it’s not clear,” Newman said. Regarding larger atmospheric patterns such as El Niño and the Quasi-Biennial Oscillation: “Maybe, but the contribution is relatively small.”
In addition to stratospheric weather, which is the main determinant of Arctic ozone levels, the authors think that long-term trends may cause ozone concentrations to reach record highs. Since the Montreal Protocol ended the production of ozone-depleting chlorofluorocarbons (CFCs) and halons in 1987, ozone levels have slowly recovered. So, the high level in March 2024 is in the authors’ expectations: Goddard’s climate-chemical model, GEOSCCM, shows a 1-in-8 probability of the highest record in 2025, and more records are anticipated in the future. However, because CFCs remain in the atmosphere for decades, average Arctic ozone will not return to 1980 levels until approximately 2045.
Higher concentrations of greenhouse gases in the stratosphere also accelerate ozone recovery. “This record may be the result of reducing ozone-depleting substances and increasing greenhouse gases. Otherwise, of course only a high year and not a record,” Newman said. “I call this year a harbinger of the future.”
NASA Earth Observatory image by Michala Garrison, using data from NASA Ozone Watch. Story by Lindsey Doermann.
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