The ozone treaty signed in the 80s successfully delayed the complete ice meltdown in the Artic by about 15 years, according to a study published in PNAS.
The Montreal Protocol was the first ever treaty to be accepted by all 198 United Nations countries and controls almost 100 chemicals classed as ozone-depleting substances (ODSs). The list includes chlorofluorocarbons (better known as CFCs), which were developed to be used as refrigerants and propellants. The original aim was to protect the ozone layer, and atmospheric concentrations of ODSs have been declining since the mid-1990s.
As many of these ODSs are also greenhouse gases, the treaty had the unexpected bonus of also helping slow down global warming. A team of international researchers, including from the University of Exeter, UK, have calculated that the treaty effectively delayed the first ice-free Artic summer — which is predicted to happen at some point in this Century — by about 15 years. The team estimates that each 1,000 tonnes of ODS emissions prevented protects about seven square kilometres of ice.
“While ODSs aren’t as abundant as other greenhouse gases such as carbon dioxide, they can have a real impact on global warming,” said Dr Mark England from the University of Exeter. “ODSs have particularly powerful effects in the Arctic, and they played a major role in driving 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.”
At the time of the treaty, many opponents predicted a wide range of negative consequences, most of which never actually happened. Instead, there are multiple cases of unintended climate benefits.
“The first ice-free Arctic summer – meaning the Arctic Ocean practically free of sea ice – will be a major milestone in the process of climate change,” said Professor Lorenzo Polvani from Columbia University. “Our findings clearly demonstrate that the Montreal Protocol has been a very powerful climate protection treaty and has done much more than healing the ozone hole over the South Pole. Its effects are being felt all over the world, especially in the Arctic.”
The team used climate model simulations to show that protecting the ozone layer itself was not responsible for slowing down the loss of Arctic sea ice. Instead, all the benefits are a consequence of controlling ODSs as greenhouse gases.
Recent research has suggested a slight increase in ODS in the last few years, and the team highlights that constant vigilance is required.
England M, Polvani L (2023) The Montreal Protocol is delaying the occurrence of the first ice-free Arctic summer. PNAS, 120 (22) e2211432120, https://doi.org/10.1073/pnas.2211432120