The Montreal Protocol of 1987 is best known for saving the ozone layer. Now scientists say it has also delayed the disappearance of Arctic sea ice. The international agreement to phase out ozone depleting chlorofluorocarbons is widely regarded as one of the most successful environmental treaties of all time.
It effectively saved the Earth’s delicate ozone layer, which protects the planet from harmful ultraviolet radiation, and the “ozone hole” in the atmosphere is on track to fully recover within a few decades. It also had unintended climatic benefits. CFCs are potent greenhouse gases and global warming would be significantly worse if they continued to be used.
That means the Montreal Protocol helped slow the Arctic’s runaway melting, a new study finds. It has likely already averted more than half a million square kilometers of sea ice loss, or nearly 200,000 square miles.
This does not mean that the treaty saved the Arctic any more than it saved the ozone layer. The Earth is steadily warming, and the Arctic is warming about three times faster than the global average. Sea ice has been declining for decades, and scientists estimate that the Arctic Ocean could experience its first ice-free summer in decades or sooner. Some research suggests that this could happen as early as 2035.
A new study published in the Proceedings of the National Academy of Sciences found that the treaty could have delayed the arrival of an ice-free summer by up to 15 years.
Researchers Mark England and Lorenzo Polvani used climate models to examine the long-term climate impact of the Montreal Protocol. In their simulations, they compared two scenarios one real world scenario and one “world-avoidance” scenario that simulates what would happen if the Montreal Protocol never existed.
It’s still not clear exactly how fast other greenhouse gases especially carbon dioxide will rise or fall in the atmosphere in the coming decades. That depends on the steps world leaders take to curb climate change.
The new study explains these uncertainties by applying two hypothetical greenhouse gas trajectories to their climate simulations.
The first is the “business as usual” scenario, which assumes no climate action between now and the end of the century. It’s a serious, if relatively unlikely, path. The second envisages moderate climate action in the coming decades, although not enough to meet the world’s climate goal of preventing a temperature rise of more than 2 degrees Celsius.
At this moderate emissions trajectory, global temperatures would be nearly 1 degree Fahrenheit warmer by mid-century in a world without the Montreal Protocol. The study also found that every metric ton of ozone-depleting substances the world avoided because of the treaty likely saved about 2,700 square miles of sea ice from melting.
The models suggest that the first ice-free summer in the Arctic would come about 15 years earlier in a world without the Montreal Protocol compared to the real world.
The study does not take into account the most recent change to the Montreal Protocol, the 2019 update known as the Kigali Amendment. It aims to phase out the use of hydrofluorocarbons, a type of chemical that replaced chlorofluorocarbons after the Montreal Protocol came into force. HFCs do not destroy the ozone, but they warm the climate.
The Kigali Amendment is expected to prevent further warming of up to 1 degree Fahrenheit between now and the end of the century. But it’s happening too late to have much of an effect on the rapidly approaching Arctic ice-free years, a new study notes.
It is not the first study to point to the climate benefits of the Montreal Protocol. Other research also concluded that the treaty has prevented a significant amount of warming over the years perhaps even more than the new study suggests. A 2021 paper in Environmental Research Letters estimates that if the Montreal Protocol did not exist, global temperatures could be as much as 1.8 degrees Fahrenheit higher by 2050.
Other scholars have focused specifically on the treaty’s effect on the Arctic. A 2020 study in Nature Climate Change suggested that ozone-depleting substances may have caused up to half of all the warming that occurred in the Arctic between 1955 and 2005.
A new study reports a similar case
“Our findings clearly show that the Montreal Protocol was a very strong climate protection treaty and did much more than cure the ozone hole over the South Pole,” Polvani, one of the study’s two authors, said in a statement. “Its effects are felt all over the world, especially in the Arctic.”