Dhe protection of the ozone layer has delayed the melting of the Arctic sea ice by up to 15 years. Because some of the substances banned by the Montreal Protocol not only damage the ozone layer, but are also powerful greenhouse gases. How the world would have developed without the ban is calculated by Mark England from the University of Exeter in England and Lorenzo Polvanic from Columbia University in New York in the journal “Proceedings of the National Academy of Sciences“ (PNAS).
In 1985, scientists discovered the ozone hole in the atmosphere over Antarctica. Because the ozone layer absorbs some of the sun’s ultraviolet rays that affect humans Cancer away from the earth’s surface, politicians reacted quickly: the Montreal Protocol to reduce and ultimately ban chlorofluorocarbons (CFCs) and similar ozone-depleting substances was signed as early as 1987 and came into force in 1989.
“Although ozone-depleting substances are not as common as other greenhouse gases, such as carbon dioxide, they can have a pronounced impact on global warming,” England is quoted as saying in a statement from his university. Because some of these substances have a global warming potential that is tens of thousands of times greater than that of carbon dioxide (CO₂). According to a previous study, without the Montreal Protocol, the global warming potential of ozone-depleting substances in 2020 would have reached about 40 percent of that year’s global warming potential of CO₂.
England and Polvanic now studied the impact of the Montreal Protocol on Arctic ice cover. With the current development, most scientists assume that the Arctic Ocean will be largely ice-free by September of each year by mid-century. The authors of the study simulated this for two scenarios of the Intergovernmental Panel on Climate Change (IPCC) – RCP8.5 and RCP4.5 – for the years 1985 to 2050. They also simulated the development for the same period, but without the Montreal Protocol.
The result depends on the greenhouse gas concentrations in the atmosphere. In scenario RCP8.5, which assumes continued very high emissions, there are already a lot of greenhouse gases in the atmosphere. Therefore, the ozone-depleting substances would account for a smaller proportion: Accordingly, their ban would only delay an ice-free Arctic in September by 7.4 years. In the more optimistic RCP4.5 scenario, which is currently considered more likely, the Montreal Protocol pushes back the timing of an ice-free Arctic September by 15 years.
The researchers assumed an annual growth rate of 3.5 percent in the use of CFCs and similar substances in the scenario without the Montreal Protocol. If they had used a rate of 7 percent, according to the simulations, the Arctic would be ice-free as early as next September. “Stopping these effects, while not the primary goal of the Montreal Protocol, was a fantastic side effect,” says England.
Incidentally, it has now been confirmed that the Montreal Protocol is effective in the original sense: According to a report by the World Meteorological Organization from 2014, the ozone hole over the Antarctic is closing more and more. If development continues, it will no longer be measurable around 2050.
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