Does that mean the ozone layer – a protective barrier against harmful UV radiation – over the Arctic is increasingly at risk?
To find the answer, a team led by the AWI experts Peter von der Gathen and Markus Rex, and by Ross Salawitch from the University of Maryland, compared the data from 53 computer models created in the context of the international “Coupled Model Intercomparison Project Phases 5 and 6” (CMIP5, CMIP6). Working from this basis, the researchers then projected the ozone depletion in the Arctic polar vortex up to the year 2100. The vortex, a relatively self-contained low-pressure system in the stratosphere at an altitude of 15 to 50 kilometres, forms over the Arctic every autumn and stays for varying durations throughout winter and spring. “For ozone to be depleted in the Arctic, the stratosphere must cool down considerably at the altitude where the ozone layer is,” says Peter von der Gathen, first author of the study. “Chlorine, which is normally bound in harmless substances, is released at low temperatures. Subsequently, chlorine together with bromine destroy ozone when exposed to sunlight. However, this only takes place when temperatures sink low enough during winter. Accordingly, in our study we estimated the ozone loss in the next few decades on the basis of the long-term temperature trend in the polar vortex and the expected decline in chlorine and bromine compounds.”
Despite the production ban issued in the 1987 Montreal Protocol, substances like chlorofluorocarbons (CFCs) and halons, which contain ozone-destroying chlorine and bromine atoms, are still abundant in the atmosphere, because they break down only very slowly. “The concentrations of these substances in the polar vortex continued to rise until the year 2000,” says Peter von der Gathen. “Since then, they’ve been on decline and are currently at roughly 90 percent of the maximum. Only by the end of the century they will have fallen below 50 percent, according to an assessment of the World Meteorological Organization. Since the pattern of warm and cold stratospheric winters in the polar vortex is very irregular, the degree of ozone depletion varies accordingly. Superimposed on this, however, our analysis of meteorological data from the past 56 years shows a significant trend toward lower temperatures in the cold stratospheric winters and associated increases in ozone losses. In addition, the analysis of the climate models clearly shows that this trend is part of climate change and therefore the product of global greenhouse-gas emissions.”