According to a new study, extremely cold winter temperatures high in the atmosphere over the Arctic are becoming more common and extreme as a result of climate patterns associated with global warming. There is a race going on in the atmosphere above the Arctic, and the ozone layer, which protects the Earth from harmful ultraviolet (UV) radiation, will lose if greenhouse gas emissions are not reduced quickly enough.
A new study led by an international team of scientists, including University of Maryland Professor Ross Salawitch, finds that extremely cold winter temperatures high in the atmosphere over the Arctic are becoming more common and extreme as a result of climate patterns associated with global warming. The study also demonstrates that the extreme low temperatures are causing reactions among chemicals that humans pumped into the air decades ago, resulting in increased ozone losses.
The new findings call into question the widely held belief that after the 2010 global ban on the production of ozone-depleting chemicals known as chlorofluorocarbons (CFCs) and halons, ozone loss would come to a halt in a matter of decades.
The study was published in the journal Nature Communications by UMD, the Alfred Wegener Institute’s Helmholtz Centre for Polar and Marine Research, and the Finnish Meteorological Institute.
A new study shows that extremely low winter temperatures high in the atmosphere over the Arctic are becoming more frequent and more extreme because of climate patterns associated with global warming.
“We’re in a race between the slow and steady decline of CFCs, which take 50 to 100 years to disappear, and climate change, which is causing polar vortex temperature extremes to become colder at a rapid pace,” said Ross Salawitch, a professor in the University of Maryland’s Departments of Atmospheric and Oceanic Science, Chemistry and Biochemistry, and Earth System Science Interdisciplinary. “CFCs deplete the ozone layer because of the increasingly cold temperatures. As a result, even though these compounds are gradually disappearing, Arctic ozone depletion is increasing as the climate changes.”
According to the study’s new data, the Arctic polar vortex temperatures and ozone losses were the lowest on record in 2020, breaking the previous record set nine years ago in 2011.
The polar vortex is a relatively self-contained low-pressure system that forms in the stratosphere over the Arctic every autumn at an altitude of about 12 to 50 kilometers (7.5 to 31 miles) and stays for varying lengths throughout the winter and spring. Because the polar vortex’s pattern of warm and cold winter temperatures is very irregular, not every winter is extremely cold.
However, the researchers are concerned about the trend toward more frequent and extremely low temperatures in the polar vortex, because those conditions promote cloud formation, which promotes ozone loss in the polar stratosphere.
The breakdown of CFCs, halons, and other ozone-depleting substances produce the majority of chlorine and a significant amount of bromine in the stratosphere. Normally, chlorine is non-reactive within the Arctic polar vortex, but clouds provide the right conditions for chlorine to change form and react with bromine and sunlight to destroy ozone.
Despite significant reductions in industrial production of CFCs and halons since the Montreal Protocol in 1987 and the subsequent global ban in 2010, these long-lasting compounds are still abundant in the atmosphere. According to the World Meteorological Organization, human-produced atmospheric chlorine and bromine are not expected to fall below 50% of their highest levels until the end of the century.
The researchers projected ozone loss out to the year 2100 based on the long-term temperature trend in the polar vortex and the expected decline in chlorine and bromine compounds to determine what this situation means for the future. They based their predictions on the output of the Intergovernmental Panel on Climate Change’s 53 top climate models.
“With the exception of one climate model,” Salawitch said, “all of the climate models we looked at show that exceptionally cold winters in the polar vortex will get colder over time.” “And the higher the level of greenhouse gas emissions, the steeper the trend, implying greater ozone depletion.”
The researchers confirmed that the Arctic is already experiencing a significant trend toward lower stratospheric temperatures and associated increases in ozone losses by combining these projections with analyses of meteorological data from the previous 56 years. Furthermore, their findings show that these trends are occurring at a rate consistent with the most recent climate models.
“We’ve been saying for a number of years that a train is coming,” Salawitch said, referring to research papers he published in 2004 and 2006 that showed extreme winters in the Arctic were becoming colder. “The train has now passed us by, with record ozone loss in 2011 and now in 2020. So, this paper is really a wake-up call that something important for ozone is happening in the atmosphere, and it appears that greenhouse gases are driving it.”
Salawitch and his colleagues do not yet fully understand how rising greenhouse gas emissions and the resulting changes in global climate are causing the polar vortex’s extremely cold winters in the stratospheric layer. However, some of the underlying mechanisms are known. Global warming occurs in part because greenhouse gases trap heat closer to the Earth’s surface, allowing cooling of the upper stratosphere, which contains the ozone layer. Warming at the surface alters prevailing wind patterns, and the researchers hypothesize that these changes result in lower temperatures in the polar vortex.
The researchers also point out that methane, a more powerful greenhouse gas than carbon dioxide, has been rapidly increasing in the lower atmosphere in recent years. As this gas rises into the stratosphere, it raises humidity, creating conditions that promote ozone-depleting chemical reactions in the Arctic.
Because ozone filters a large portion of the sun’s potentially harmful UV radiation, a depleted ozone layer over the Arctic can result in more UV radiation reaching the Earth’s surface over Europe, North America, and Asia when the polar vortex dips south.
According to the researchers, there is still hope for avoiding future ozone depletion. Their research shows that significant reductions in greenhouse gas emissions over the next few decades could result in a steady decline in conditions that favor large ozone losses in the Arctic stratosphere.
The study, Climate change favors large seasonal loss of Arctic ozone, was published in the journal Nature Communications by Peter von der Gathen, Rigel Kivi, Ingo Wohltmann, Ross J. Salawitch, and Markus Rex. NASA’s Atmospheric Composition and Modeling Program (Award No. 80NSSC19K0983) and the Multidisciplinary Drifting Observatory for the Study of Arctic Climate (MOSAiC) expedition provided funding for this research. The views expressed in this article do not necessarily reflect those of these organizations.
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