A 1980s environmental pact once dubbed the "single most successful international agreement to date" might have unintentionally given us an extra decade or two to fight climate change, a new study has found.
Last week, the UN's Intergovernmental Panel on Climate Change issued a report saying we're on track to hit 1.5C of warming by 2030, increasing the risk of the climate reaching irreversible tipping points if we don't slash emissions immediately.
But we might already have reached "scorched earth" if it weren't for a global deal to phase out the use of chlorofluorocarbons - used in aerosol cans and refrigerators - signed way back in 1987.
The intent of the Montreal Protocol on Substances that Deplete the Ozone Layer - to use its full name - was to save the ozone layer, which protects life on Earth from damaging UV rays. The success of the agreement - dropping use of ozone-depleting substances by 99.7 percent - has led scientists to predict the layer will have recovered by the mid-21st century. Former head of the UN Kofi Annan called it "perhaps the single most successful international agreement to date".
The protocol's text doesn't actually mention climate change or global warming - but it was later found that CFCs were a potent greenhouse (GHG), thousands of times more so than even carbon dioxide. Researchers in 2019 estimated the Montreal Protocol had done eight times more to slow down global warming than 1997's warming-focused Kyoto Protocol, saving us 1C by 2050.
But the cooling effect might be even bigger than that. A new study involving scientists from the US, UK and New Zealand has found the UV rays that would have reached the Earth's surface if the Montreal Protocol never happened would have badly damaged plants' ability to store carbon dioxide.
Without Montreal, their modelling shows the ozone layer would have largely collapsed by 2040, particularly over the tropics where much of the world's vegetation is.
"Increased UV would have stopped plants being able to soak up so much carbon from the atmosphere which would have led to greater global warming," said Olaf Morgenstern, atmospheric scientist at New Zealand's National Institute of Water and Atmospheric Research (NIWA).
Thanks to this, by the end of the century there would be 580 billion tonnes more carbon dioxide in the atmosphere, the scientists calculated - about 13 years' worth of current global carbon dioxide emissions. Concentrations in the atmosphere would be up an extra 215 parts per million, about 50 percent more than what there already is, resulting in another 0.8C of warming on top of the increased risk of skin cancers.
"Without the protocol human health would have been severely impacted and UV would be catastrophic for vegetation."
The study found the warming effect of the continued use of CFCs would have added another 1.7C to global temperatures too, all up resulting in 2.5C of warming on top of the influence of other GHGs like carbon dioxide and methane.
CFCs were replaced with hydrofluorocarbons (HFCs), which are also being phased out - while they're much better for the ozone layer, they also contribute to warming much more strongly than carbon dioxide. Some scientists have even suggested replacing both with carbon dioxide itself, saying it's a much weaker GHG and leaves the ozone layer alone.
An amendment to the Montreal Protocol phasing out HFCs is expected to save another 0.5C of potential warming by 2100.
The latest study was published Thursday in Nature.
