Montreal Protocol has slowed loss of Arctic sea ice, say scientists

According to new research, the Montreal Protocol, which attempts to reduce emissions of ozone-depleting gases, has the unexpected benefit of delaying the disappearance of Arctic sea ice.

In an effort to stem the loss of the ozone layer above the earth, nearly 200 nations pledged to reduce their emissions of “ozone-depleting substances” when they signed the historic Montreal Protocol in 1987.

The accord has received high praise for being one of the best environmental treaties ever put into practise.

The ozone layer is on course to fully recover in the ensuing decades thanks to the phase-out of approximately 99% of compounds that were once prohibited for degrading the ozone layer, such as chlorofluorocarbons (CFCs).

The deal has, nevertheless, also produced some unanticipated advantages.

The Montreal Protocol has already prevented about 0.5C of global warming by reducing the emissions of several of the chemicals that are prohibited by the accord. These compounds are potent greenhouse gases.

The analysis, which was published in the Proceedings of the National Academy of Sciences , indicates that by preventing regional warming, the Montreal Protocol prevented the loss of more than 500,000 square kilometres of Arctic summer sea ice by 2020.

Many experts anticipate the first “ice free” summer in the Arctic around the middle of the century, however the region’s destiny is still uncertain. The Montreal Protocol, according to the authors, is already putting off this day by about 15 years. They say that this historic agreement will have prevented an increase in Arctic warming of 0.88C by 2050. (The Arctic has warmed faster than the average global temperature.)

According to the study’s primary author, “I think this should give us hope.” He adds that the achievement of the Montreal Protocol “should encourage us that action on climate is possible” because the international community “took really quick action.”

The Montreal Protocol

Life on earth depends on the stratospheric ozone layer , which is a thick layer of ozone gas that lies 15 to 30 kilometres above the surface of the planet. It serves as a shield, shielding plant and animal life from the sun’s harmful UV rays.

The ozone layer was found to be thinning in the late 1970s when scientists realised that man-made substances known as halocarbons were reacting with the ozone gas. A team of scientists discovered in 1985 that an alarming “hole” was developing in the ozone layer over Antarctica each spring. Their research became a landmark paper on the subject after it was published in Nature.

To defend the ozone layer, the world community acted quickly. Two years later, the Montreal Protocol was ratified by 197 nations. Signatories to this agreement committed to phasing out their emissions of about 100 different “ozone depleting substances” quickly.

Ozone-depleting halocarbons were often employed as cleansers, spray can propellants, and coolants in refrigerators before the agreement was signed. After the agreement was reached, these were swiftly replaced by non-ozone-depleting hydrofluorocarbons (HFCs). The ozone layer is expected to fully recover in the upcoming decades thanks to the phase-out of approximately 99% of the banned ozone-depleting chemicals now in use.

According to main author of the study and senior research fellow at The University of Exeter, Dr. Mark England, the Montreal Protocol is “the most successful climate treaty to date,” he told Carbon Brief.

When the Montreal Protocol was put into effect, he claims there was “scaremongering and fear mongering” about its effects, with many claiming that countries would go bankrupt if they phased out commercially significant gases. He adds that the deal was effective in large part because the international community took “really quick action,” but claims that “none of that came to pass.”

‘World avoided’

The study uses models from the fifth coupled model intercomparison project, a framework that scientists use to compare several models, to examine the impact of the Montreal Protocol on human-caused emissions of CFC and HFC gases throughout the period of 1960–2050.

The authors run the models for both very high warming (RCP8.5) and moderate warming (RCP4.5). Following the implementation of the Montreal Protocol, ozone depleting chemical emissions in both scenarios rapidly decline while levels of the replacement gas, HFC, increase. In either case, it is anticipated that the ozone layer would fully recover during the following decades.

Additionally, the study offers a fictitious “world avoided” case in which the Montreal Protocol was never ratified. While HFC levels continue to be modest, ozone depleting chemical levels progressively increase by 3.5% year. In this scenario, the ozone layer in the Arctic progressively deteriorates during the ensuing decades.

The Montreal Protocol has the unforeseen effect of decreasing global warming in addition to limiting ozone depletion. Since the Montreal Protocol restricts the emissions of many chemicals that are strong greenhouse gases, it has already prevented 0.5C of warming

According to the study, HFCs, which have mostly replaced CFCs, also contribute to global warming. Their warming effect on surface temperatures, however, is “more than an order of magnitude smaller” than that of their ozone-depleting counterparts, claims the study.

Arctic ice

One of the most obvious and recognisable effects of climate change is melting sea ice. The authors found that the Montreal Protocol has already stopped a rise in surface temperature of 0.88C in the Arctic, where warming is occurring More faster than the global average

The authors map the area of the Arctic sea ice under several scenarios in order to more thoroughly examine changes in the sea ice cover.

The study concludes that by 2020, the Montreal Protocol had already reduced the loss of Arctic sea ice by more than 500,000 square kilometres. The Montreal Protocol will have saved one million square kilometres by 2030 and two million by 2040 under a moderate emissions scenario, it continues.

According to the scientists, every tonne of ozone depleting compounds avoided prevents the loss of about 7,000 square kilometres of Arctic sea ice. In contrast, they assert that a tonne of avoided CO2 emissions only preserves three square kilometres of Arctic sea ice.

Ice-free summer

Every summer, the Arctic sea ice shrinks and melts due to rising temperatures. September is typically when the yearly minimum sea ice extent is reached.

Around 13% less Arctic sea ice is present annually on average per decade, and by the middle of the century, experts predict that the region will see its first “ice-free” summer. Instead of zero sea ice cover, a “ice-free” summer refers to a sea ice extent of less than one million square kilometres

The first Arctic summer without ice will “captivate people’s attention” and represent “a step change in how we view our climate system,” England tells Carbon Brief.

The authors run their models tens of thousands of times with slightly varied initial circumstances in order to determine when the first summer in the Arctic would be ice-free. They then use the results to illustrate the likelihood that the first summer in the Arctic will occur in various years. They do this again for the RCP8.5 and RCP4.5 scenarios, using the “standard” scenario of the current climate and the world averted scenario, in which the Montreal Protocol was never signed, respectively.

Dr. Zack Labe, a postdoctoral researcher at Princeton University’s Atmospheric and Oceanic Sciences Programme and the NOAA Geophysical Fluid Dynamics Laboratory, was not engaged in the study.

Due to the great natural fluctuation in the Arctic, he tells Carbon Brief that it is “challenging” to estimate when the first ice will melt. He adds that running the climate models numerous times helps to account for this natural variability.

According to the scientists’ projections, the first Arctic summer without ice will occur in 2049 under RCP4.5. However, if the Montreal Protocol had not been put into effect, this milestone would have been anticipated around 15 years sooner.

The first Arctic ice-free year would have been recorded in 2040 and 2033 with and without the Montreal Protocol, according to the paper’s very high warming RCP8.5 scenario.

The authors state that this estimate is cautious. The analysis makes the assumption that ozone depleting petrol emissions would have increased by 3.5% annually in the absence of the Montreal Protocol. The authors do point out that a range of 3-7% is feasible.

According to England, the first Arctic summer without ice “could be happening today” if the Montreal Protocol had not been put into effect and ozone-depleting chemical emissions had increased by 7% annually.

According to Labe, the study is “really fascinating” and “accessible, clear, and concise.”

The Kigali Amendment

Nearly 200 nations agreed to reduce HFC emissions when they ratified the Kigali amendment to the Montreal Protocol in October 2016. According to the accord, rich nations began limiting their usage of HFCs in 2019 and developing nations promised to follow suit starting in the middle to late 2020s.

The Kigali amendment is not simulated by the authors in their model. According to them, the modification will prevent heat from rising by more than 0.05C by 2035 and won’t significantly affect data from the first Arctic summer without ice.

Dr. Amna Jrrar, an ozone and sea ice modelling expert at the Royal Scientific Society in Jordan who was not involved in the study, is a research scientist there. She concurs that incorporating the Kigali amendment would not “significantly affect the study’s findings.”

The Kigali Amendment, according to the report, will nevertheless be significant in the long run since it will prevent global temperatures from rising by 0.3 to 0.5C by the end of the century.

Dr. Yu-Chiao Liang, an assistant professor at National Taiwan University, also issues a warning that the study’s findings may be impacted by a recent increase in emissions of five CFC chemicals that are prohibited. The study’s author Liang, who was not participating, issues a dire warning: “If these emissions continue, it is likely that the Arctic warming will be further amplified and the ice-free summer will come earlier.”

England yet claims that this is a “positive story” for Carbon Brief. He continues:

“We have made good decisions and experienced genuine climatic benefits that are explicable by models. I believe that this should cheer us and give us hope that we may still make a difference in the environment in the coming decades.

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