(CN) — The Montreal Protocol — the only United Nations treaty ratified by every country in the world — plays a key role in delaying the first ice-free Arctic summer until 2050, though a research team reports that further delay of such an occurrence also depends on future carbon dioxide emissions.
“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 Professor Lorenzo Polvani, a professor of geophysics and earth and environmental sciences at Columbia University.
Per the study published Monday in Proceedings of the National Academy of Science, the Montreal Protocol came about when scientists discovered a hole in the ozone over Antarctica in 1985, creating worldwide alarm as the ozone layer shields Earth and its inhabitants from harmful levels of ultraviolet radiation.
In 1987, the United Nations signed the Montreal Protocol to reduce atmospheric concentrations of ozone-depleting substances (ODS), potent greenhouse gases commonly used in refrigerators and aerosols that study co-author Dr. Mark England explained via email are dangerous in their longevity.
“Ozone depleting substances are stable and do not break down in the lower atmosphere, allowing them to last for many years, even decades, and can be transported high into the stratosphere,” wrote England, Royal Commission for the Exhibition of 1851 senior research fellow at the University of Exeter. “When they reach the stratosphere, they are broken down by solar radiation, and go on to deplete ozone over Antarctica where the temperatures are cold enough for this to occur. However, for this study, the importance of ozone depleting substances is as greenhouse gases which warm the climate in a similar fashion to CO2 but are in fact much more powerful on a molecule-by-molecule basis.”
Researchers estimate that since the Montreal Protocol went into effect in 1989, every 1,000 tons of ODS emission it prevented saved seven square kilometers of Arctic Sea ice.
Furthermore, the researchers tested two scenarios, one involving a world with the Montreal Protocol and one without it between 1985 and 2050, and they estimated that a world without the Montreal Protocol had a global mean surface temperature 0.5 degrees Celsius warmer in 2050 than one with it, with the Arctic polar cap almost one degree Celsius warmer.
“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,” said England.
And though Polvani and England urge everyone to remain vigilant as recent research suggests a slight rise in ODS concentrations from 2010 to 2020, they remain optimistic.
“Our study adds another layer to the climate benefits of the Montreal Protocol and is a rare good news story in the field of climate science," wrote England. “Taking early action was key in the case of the Montreal Protocol and we are continuing to live with the Arctic climate benefits today. One surprising finding was that if we hadn’t enacted the Montreal Protocol and had continued to emit Ozone Depleting Substances at high rates, it is possible that we could be experiencing the first ice free Arctic summer around the present day.”
“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,” said Polvani.
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