State of the Planet

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Montreal Protocol Is Delaying First Ice-Free Arctic Summer

This story was originally published by Columbia Engineering.

When scientists discovered a hole over Antarctica in 1985, countries across the globe got together and wrote a treaty designed to protect the ozone layer, which shields the Earth—and us—from harmful levels of ultraviolet radiation. The resulting Montreal Protocol, the only United Nations treaty ratified by every country in the world, was signed in 1987 and entered into effect in 1989, when little was known about its impact on the global climate. Its purpose was to reduce atmospheric concentrations of ozone-depleting substances, such as materials commonly used in products such as refrigerators, air conditioners, fire extinguishers, and aerosols. For more than 50 years, it has been an important mitigation treaty, affecting many aspects of the global climate.

An iceberg in the Arctic with underside visible
An iceberg in the Arctic Ocean. Credit: AWeith via CreativeCommons

The Benefits of the Mitigation Treaty

A new study led by climate researchers at Columbia Engineering and the University of Exeter demonstrates that the treaty’s impact reaches all the way into the Arctic: its implementation is delaying the occurrence of the first ice-free Arctic by as much as 15 years, depending on the details of future emissions. The study was published today by PNAS.

“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 the study’s co-author Lorenzo Polvani, Maurice Ewing and J. Lamar Worzel Professor of Geophysics in the department of applied physics and applied mathematics and professor of earth and environmental 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.”

The Impact of Ozone-Depleting Substances

Polvani noted that the rapid melting of Arctic sea ice is the largest and clearest signal of anthropogenic climate change. Current projections indicate that the first ice-free Arctic summer will likely occur by 2050, owing largely to increasing carbon dioxide concentrations in the atmosphere. However, other powerful greenhouse gases have also contributed to Arctic sea ice loss, notably ozone-depleting substances. When these substances became strictly regulated by the Montreal Protocol In the late 1980s, their atmospheric concentrations began to decline in the mid-1990s.

Polvani and his co-author Mark England, Royal Commission for the Exhibition of 1851 Senior Research Fellow at the University of Exeter and a former PhD student with Polvani, were particularly interested in exploring the impact of ozone-depleting substances because their molecules, while a lot less common in the atmosphere, are tens of thousands of times more powerful at warming the planet than carbon dioxide.

New Climate Model Simulations

The researchers analyzed new climate model simulations and found that the Montreal Protocol is delaying the first appearance of an ice-free Arctic summer by up to 15 years, depending on future CO2 emissions. They compared the estimated warming from ozone-depleting substances with and without the Montreal Protocol under two scenarios of future CO2 emissions from 1985–2050. Their results show that if the Montreal Protocol had not been enacted, the estimated global mean surface temperature would be around 0.5 degrees Celsius warmer and the Arctic polar cap would be almost 1 degree Celsius warmer in 2050.

“This important climate mitigation stems entirely from the reduced greenhouse gas warming from the regulated ozone-depleting substances, with the avoided stratospheric ozone losses playing no role,” said England. “While ozone-depleting substances aren’t as abundant as other greenhouse gasses such as carbon dioxide, they can have a real impact on global warming. Ozone-depleting substances 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.”

Since the mid-1990s, the Montreal Protocol has successfully reduced atmospheric concentrations of ozone-depleting substances and there are signs that the ozone layer has started to heal. But recent research has suggested a slight rise in ozone-depleting substance concentrations from 2010–2020, and England and Polvani stressed the importance of staying vigilant.

Learn more about Lorenzo Polvani and his research:

Columbia campus skyline with text Columbia Climate School Class Day 2024 - Congratulations Graduates

Congratulations to our Columbia Climate School MA in Climate & Society Class of 2024! Learn about our May 10 Class Day celebration. #ColumbiaClimate2024

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