CLIMATE WIRE | The 1987 Montreal Protocol is best known for saving the ozone layer. Now scientists say it 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 rays, and the “ozone hole” in the atmosphere is on track to fully recover within decades.
It also had unintended climatic benefits. Chlorofluorocarbons are potent greenhouse gases and global warming would have been much worse had they remained in use.
This means that the Montreal Protocol has helped slow the rapid melting of the Arctic, a new study find. It has probably already avoided 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, as it saved the ozone layer. The Earth is warming steadily and the Arctic is warming at about three times the global average rate. Sea ice has been shrinking for decades, and scientists estimate the Arctic Ocean could experience its first ice-free summer within decades or less. Some research suggests this could happen as early as 2035.
The new study, published in Proceedings of the National Academy of Sciencesfinds that the treaty may have delayed the onset of ice-free summers by up to 15 years.
Researchers Mark England and Lorenzo Polvani used climate models to study the long-term climate impact of the Montreal Protocol. They compared two scenarios in their simulations – a real-world scenario and an “avoided world” scenario, which simulates what would have happened if the Montreal Protocol had never existed.
It is still unclear exactly how fast other greenhouse gases – carbon dioxide, in particular – will increase or decrease in the atmosphere in the coming decades. It depends on what actions world leaders take to curb climate change.
The new study accounts for these uncertainties by applying two hypothetical greenhouse gas trajectories to their climate simulations.
The first is a “business-as-usual” scenario that assumes little or no climate action occurs by the end of the century. It is a serious path, although relatively unlikely. The second assumes moderate climate action in the coming decades, albeit insufficient to meet the global climate goal of preventing a temperature rise above 2 degrees Celsius.
According to 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 finds that every metric ton of ozone-depleting substances the world avoided through the treaty likely avoided the melting of about 2,700 square miles of sea ice.
Models indicate that the Arctic’s first ice-free summer would occur 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 amendment to the Montreal Protocol, a 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 entry into force of the Montreal Protocol. HFCs do not destroy ozone, but they warm the climate.
The Kigali Amendment is expected to prevent up to 1 degree Fahrenheit of additional warming by the end of the century. But that’s happening too late to have a big effect on Arctic ice-free summers, which are rapidly approaching, the new study notes.
This is not the first study to highlight the climate benefits of the Montreal Protocol. Other research has also concluded that the treaty has prevented a substantial amount of warming over the years – perhaps even more than the new study suggests. An article from 2021 In Environmental Research Letters estimated that global temperatures could be up to 1.8 degrees Fahrenheit higher by 2050 if the Montreal Protocol did not exist.
Other scientists have looked specifically at the effect of the treaty on the Arctic. A 2020 study In Natural climate change suggested that ozone-depleting substances may have driven up to half of all warming experienced in the Arctic between 1955 and 2005.
The new study makes a similar case.
“Our results clearly demonstrate that the Montreal Protocol has been a very powerful climate protection treaty and has done much more than cure the ozone hole over the South Pole,” said Polvani, one of the two authors of the study, in a press release. “Its effects are being felt all over the world, especially in the Arctic.”
Reprinted from E&E news courtesy of POLITICO, LLC. Copyright 2023. E&E News provides essential information for energy and environmental professionals.