A global agreement in the 1980s to cut CFCs and save the ozone layer has had an unexpected spinoff benefit.
New research has found the Montreal Protocol, signed in 1987, has done more to slow global warming than 1997's Kyoto Protocol, which was directly aimed at stemming greenhouse gas emissions.
And it's not even close - Montreal's been about eight times more effective than Kyoto at slowing warming, despite it not being the goal.
"By mass CFCs are thousands of times more potent a greenhouse gas compared to carbon dioxide, so the Montreal Protocol not only saved the ozone layer but it also mitigated a substantial fraction of global warming," said lead author of the paper Rishav Goyal.
"Remarkably, the protocol has had a far greater impact on global warming than the Kyoto Agreement, which was specifically designed to reduce greenhouse gases. Action taken as part of the Kyoto Agreement will only reduce temperatures by 0.12C by the middle of the century - compared to a full 1C of mitigation from the Montreal Protocol."
Scientists used a conservative guess of 3 percent growth in CFC use since 1987 - much less than what was happening in reality - and say the 1C of warming prevented by 2050 is probably and underestimate.
They also found ice cover in the Arctic would be 25 percent lower today if CFCs weren't phased out.
"Without any fanfare the Montreal Protocol has been mitigating global warming impacts for more than three decades, surpassing some treaties that were specifically aimed to ameliorate climate change impacts," said co-author Martin Jucker.
A previous study found the Montreal Protocol reduced skin cancer rates by about 15 to 18 percent by helping close the hole in the ozone layer. Former Secretary-General Kofi Annan called it the "perhaps the single most successful international agreement to date".
And in 2016, scientists estimated the hole had shrunk by 4 million square kilometres - about half the size of Australia.
"Montreal sorted out CFCs, the next big target has to be zeroing out our emissions of carbon dioxide," said co-author Matthew England.
CFCs were used as refrigerants, propellants and solvents.
They haven't been entirely wiped out though - emissions have been increasing since 2013 thanks to rogue operators in China.
The latest study was published in journal Environmental Research Letters.
