The Montreal Protocol was adopted in 1987 in order to protect the ozone layer. An unpredicted side effect of its strict regulation of ozone-depleting substances has been to slow global warming, delaying the occurrence of the first ice-free summer in the Arctic by up to 15 years
Based on current projections, the first ice-free summer in the Arctic is expected in 2050. The cause is largely increasing atmospheric carbon-dioxide concentrations and the higher temperatures they cause. However, the fact that Arctic sea ice is not retreating even faster can be credited to the 1987 Montreal Protocol. Had it not been for its strict regulation of ozone-depleting substances, the first ice-free summer in the Arctic would likely take place 15 years sooner, according to recently published research.
“The first ice-free Arctic summer — with the Arctic Ocean practically free of sea ice — will be a major milestone in the process of climate change, and our findings were a surprise to us,” said Lorenzo Polvani, a professor of geophysics and earth and environmental sciences at Columbia University and one of the authors of the paper, published in Proceedings of the National Academy of Sciences. “Our results show that the climate benefits from the Montreal Protocol are not in some faraway future: the protocol is delaying the melting of Arctic sea ice at this very moment. That’s what a successful climate treaty does: it yields measurable results within a few decades of its implementation.”
When the agreement was adopted, little was known about the impact it would have on climate change. It is now known that, in addition to carbon dioxide and methane, other powerful greenhouse gases are contributing to warming and thus to the loss of Arctic sea ice. The most notable of these are ozone-depleting substances — chemicals such as chlorofluorocarbons (CFCs and HCFCs), halons and methyl bromide — that all saw their atmospheric concentrations decline as a result of the strict regulations implemented by the Montreal Protocol beginning in the mid-1990s.
In their research, Mr Polvani and his colleague, Mark England, a senior research fellow at the University of Exeter, were particularly interested in the effects of ODS because they are much less abundant in the atmosphere than carbon dioxide but are ten thousand times more potent greenhouse gases. Comparing different climate model simulations, they found that, without the agreement, the estimated global mean surface temperature in 2050 would be about 0.5°C higher, and that in the Arctic polar ice cap it would be 1°C higher.
“This important climate mitigation stems entirely from the reduced greenhouse-gas warming from the regulated ODSs, with the avoided stratospheric ozone losses playing no role,” Mr England said. “While ODSs aren’t as abundant as other greenhouse gases such as carbon dioxide, they can have a real impact on global warming. ODSs have particularly powerful effects in the Arctic, and they were an important driver of Arctic climate change in the second half of the 20th century. While stopping these effects was not the primary goal of the Montreal Protocol, it has been a fantastic by-product.”
Thanks to the treaty, the ozone layer appears to be recovering, though recent research suggests a slight increase in ODS concentrations between 2010 and 2020. Messrs England and Polvani therefore stress the importance of keeping an eye on it.
The ozone layer shields the Earth from harmful ultraviolet radiation. After the discovery of a hole in the ozone layer over Antarctica in 1985, countries around the world drew up the Montreal Protocol in order to address the causes of its disappearance. It is the only UN treaty that has been ratified by every country. ODSs were used in a number of products, including refrigerators, air conditioners, fire extinguishers and aerosols.
Julia Hager, PolarJournal
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