From NASA Earth Observatory:
Ozone concentrations over the Arctic reached a record high monthly average in March 2024. Due to large-scale weather systems that disrupted the upper atmosphere during the winter of 2023-2024, more ozone than ever before entered the stratosphere over the Arctic and remained there for another 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 lack of high Arctic ozone levels since the 1970s,” the authors wrote, “the record high in March 2024 should be viewed as a positive harbinger of the future Arctic ozone layer.”
Between December 2023 and March 2024, a series of planetary waves propagated upward through the atmosphere, slowing the stratospheric jet stream circulating around the Arctic. When that happens, midlatitude air converges at the pole, sending ozone into the Arctic stratosphere. In addition to the ozone influx, there was very little of the typical ozone depletion from substances like chlorine, said Paul Newman, chief scientist for geosciences at NASA's Goddard Space Flight Center and lead author of the study. “It was a very dynamic, active winter in the northern hemisphere,” he said.
More stratospheric ozone has a positive impact on 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 2024, the UV index was 6 to 7 percent lower in the Arctic and 2 to 6 percent lower in the mid-latitudes of the Northern Hemisphere. Less UV radiation means less damage to plant DNA and a lower risk of cataracts, skin cancer and weakened immune systems in people and animals.
The activity in March 2024 is in sharp contrast to March 2020, when ozone concentrations in the stratosphere reached extremely low levels. Without interference from wave events in the upper atmosphere, steady circumpolar winds prevented ozone from other latitudes from refilling the Arctic stratosphere. The stable polar vortex also created colder-than-average conditions, which encouraged the occurrence of ozone-depleting reactions.
The maps above show the ozone concentrations over the Arctic for March 2020 (left) and March 2024 (right) and illustrate the large fluctuations possible there. The monthly averages were calculated by the NASA Ozone Watch team and based on data collected by the OMPS (Ozone Mapping Profiler Suite) on the NASA-NOAA Suomi-NPP satellite.
Unlike over Antarctica, where ozone holes form every year, ozone concentrations over the Arctic fluctuate widely and are subject to the “annual fluctuations” of tropospheric and stratospheric weather, Newman said.
1979 – 2024
The strong wave events from late December 2023 to early March 2024 resulted in the increases in ozone concentrations shown in the graph above. As usual, ozone levels peaked in March and then remained well above average. The months of May, June, July and August also set new records for monthly average ozone concentrations. “This is truly an exceptional summer period in the north,” Newman said.
As for what could be the cause of the unusual stratospheric weather, the authors examined various factors without finding a clear answer. The effects of climate change, for example, are difficult to quantify. “There could be a climate factor here, but it’s not obvious,” Newman said. Regarding larger atmospheric patterns such as El Niño and the quasi-biennial oscillation: “Possible, but the contribution is relatively small.”
In addition to stratospheric weather being the primary influence on ozone levels in the Arctic, the authors suggest that longer-term trends likely caused 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 been slowly recovering. Therefore, the high values in March 2024 were within the authors' expectations: the Goddard chemical climate model GEOSCCM showed a 1 in 8 chance of a record high by 2025, and further records are expected in the future. However, because CFCs remain in the atmosphere for decades, average Arctic ozone is not expected to return to 1980 levels until around 2045, they note.
Higher concentrations of greenhouse gases in the stratosphere also accelerate ozone recovery. “This record was likely due to a decrease in ozone-depleting substances and an increase in greenhouse gases. Otherwise it would have just been a peak year and not a record year,” Newman said. “I call this year a harbinger of the future.”
NASA Earth Observatory images by Michala Garrison, using data courtesy of NASA Ozone Watch. Story by Lindsey Doermann.
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