Last year, scientists reported a large, seemingly open hole in the ozone layer above the Arctic. The hole is mysterious because it doesn't usually happen.
Now, researchers have found that the hole is likely caused by a series of events triggered by record sea surface temperatures in the North Pacific, according to a new study reported in Advances in Atmospheric Sciences.
The hole in the ozone layer, refers to the 'patch' over Antarctica in the southern hemisphere during the Australian springtime around September, October and November each year. The Arctic in the Northern Hemisphere is usually too warm for polar stratospheric clouds to form, which is the main driver of the ozone depletion process in the spring.
But in the spring of 2020, an unprecedented hole formed over the North Pole. Scientists from the Chinese Academy of Sciences used satellite data and simulations to show that the hole was the impact of record North Pacific sea surface temperatures that occurred between February and March.
These warmer sea surface temperatures, contributed to the weakening of important planetary waves (which help transfer heat from the tropics to the poles, and cold air from the poles to the tropics to maintain atmospheric balance), which contributed to the Aleutian low, a large atmospheric low point that its center of pressure often resides over the Aleutian Islands near the Gulf of Alaska each winter.
The result of this knock-on effect is a very cold and persistent stratospheric polar vortex between February and April 2020, allowing the formation of polar stratospheric clouds that break up the ozone layer.
The ozone layer is the region of the stratosphere between 15 and 30 kilometers above the Earth's surface that has a high concentration of gaseous ozone. This layer absorbs much of the Sun's harmful ultraviolet rays, acting as an invisible shield for our planet.
Unfortunately, this coating is degraded by chlorofluorocarbons (CFCs), man-made chemicals that were once widely used in aerosol sprays, solvents, and as refrigerator coolants. CFCs stay in the air long enough to float up into the stratosphere.
Although CFCs were phased out under the Montreal Protocol in the late 1980s, they continued to hide in Earth's atmosphere for some time. CFCs are especially problematic when there is formation of polar stratospheric clouds, high-altitude clouds that can help increase chemical reactions involving CFCs that cause ozone depletion.
So far, the Montreal Protocol is considered a remarkable success. It is the only United Nations (UN) environmental treaty ratified by every country in the world, and the ozone layer, as a whole, is in much better shape than it was three decades earlier. However, as this study shows, the problem of CFCs and ozone depletion continues to haunt our planet.
"The establishment of record Arctic ozone loss in the spring of 2020 indicates that current ozone-depleting substances are still sufficient to cause severe spring ozone depletion in the Arctic stratosphere," said lead author Professor Yongyun Hu of the Laboratory for Climate and Ocean-Atmosphere Studies at the University of Pekingese.
"These results suggest that severe ozone loss is likely to occur in the near future as long as the warm North Pacific sea surface temperature anomaly or other dynamic process is sufficiently strong."
