The Montreal Protocol of 1987, a global deal to protect the ozone layer, has been found to delay the first ice-free Arctic summer by up to 15 years, according to a new research.
The deal, which was the first treaty to be ratified by every United Nations country, regulated nearly 100 man-made chemicals called ozone-depleting substances (ODSs) to preserve the ozone layer, which protects humans and the environment from harmful levels of ultraviolet radiation.
ODSs are compounds developed in the last century for industrial use as refrigerants and propellants.
The researchers from University of California Santa Cruz (US), Columbia University (US) and the University of Exeter (UK) estimated that each 1,000 tonnes of ODS emissions prevented saves about seven square kilometres of Arctic sea ice.
The research, published in the journal Proceedings of the National Academy of Sciences (PNAS), showed that a reduction in the ODSs, which are also potent greenhouse gases, has slowed down global warming, despite the treaty's main aim being to preserve the ozone layer.
"While ODSs aren't as abundant as other greenhouse gases such as carbon dioxide, they can have a real impact on global warming," said Mark England, senior research fellow at the University of Exeter.
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"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," said England.
This study, using new climate model simulations, showed that the effects of this included delaying the first ice-free Arctic summer, currently projected to happen in the middle of this century, by up to 15 years, depending on future emissions.
The study also showed that protection of the ozone layer itself played no part in slowing the loss of Arctic sea ice - all the benefits related to the role of ODSs as greenhouse gases.
"While stopping these effects was not the primary goal of the Montreal Protocol, it has been a fantastic by-product," said England.
England said opponents of the protocol predicted a range of negative consequences, most of which did not happen, and instead there are numerous documented instances 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.
"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," said Lorenzo Polvani, from Columbia University.
The study said that this effort had succeeded, with atmospheric concentrations of ODSs declining since the mid-1990s and signs that the ozone layer had started to heal.
However, with the research suggesting a slight rise in ODS concentrations from 2010-20, vigilance was still required, said England.
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