The ozone-wrecking chemicals once commonly used in refrigerators would have driven 2.5C of extra global heating by the end of the century if they had not been banned, research has found.
Modelling by climate scientists found that the 1987 Montreal protocol curbing chlorofluorocarbons (CFCs) gave humans a fighting chance of limiting global heating to 1.5C as set out by the Paris agreement.
The atmosphere has already warmed 1.1C to 1.2C above pre-industrial levels, meaning the Earth could have been facing 3.5C of warming if CFCs were still in use.
As well as refrigerators, CFCs were used in insulation foams and aerosols.
The modelling by teams in the UK, US and New Zealand was based on a theoretical rise in CFC use of 3% a year from 1987.
It found ongoing depletion of ozone – the gas that protects the planet from harmful levels of ultra violet radiation (UV) – would have massively undermined the Earth’s ability to absorb carbon dioxide (CO2) from the atmosphere.
The world would already be experiencing the worst-case scenario levels of global warming that are predicted if international leaders fail to meet their net zero CO2 commitments.
Protecting the ozone layer shielded global vegetation from damaging increases in UV that undermines plant life’s ability to absorb CO2.
Hikes in UV can damage plant tissues, restrict their growth and undermine their ability to photosynthesise – the process that sucks carbon from the atmosphere.
Without the CFC ban, there would have been 580bn fewer tonnes of carbon stored in forests, vegetation and soil by 2100, the researchers found.
There would be an additional 165-215 parts per million of CO2 in the atmosphere – based on projected fossil fuel emissions – compared with present-day levels of 420 parts per million, or a jump of 40% to 50%.
This additional CO2 would have contributed an additional 0.8C of warming, the researchers said, leaving the goals of the Paris Agreement in tatters.
As well as depleting the ozone layer, CFCs are also powerful greenhouse gases.
If their use had continued unchecked, by the end of the century they would have boosted global warming by another 1.7C – meaning temperatures would have risen 2.5C overall just from their use.
Dr Paul Young, lead author from Lancaster University, said: “A world where these chemicals increased and continued to strip away at our protective ozone layer would have been catastrophic for human health, but also for vegetation.”
He added: “With our research, we can see that the Montreal protocol’s successes extend beyond protecting humanity from increased UV to protecting the ability of plants and trees to absorb CO2.
“Although we can hope that we never would have reached the catastrophic world as we simulated, it does remind us of the importance of continuing to protect the ozone layer.
“Entirely conceivable threats to it still exist, such as from unregulated use of CFCs.”
In 2018, atmospheric scientists spotted a resurgence of levels of CFC-11, traced to rogue insulation production in eastern China.
The Chinese authorities confirmed some banned substances were identified during factory inspections but only in very small quantities.
Officials said arrests, material seizures and the demolition of production facilities then followed and emissions of CFC-11 have since fallen rapidly.
Even without CFCs, carbon dioxide levels are still thought to be at their highest levels in human history.
The research also found by 2100 there would have been 60% less ozone above the tropics.
This would have been an even worse situation than was seen when an ozone hole formed above the Antarctic at the height of CFC use in the 1980s.
By 2050, levels of cancer-causing UV light in the mid-latitudes – covering most of Europe, the UK, the US and central Asia – would have been stronger than the present-day tropics.
The paper The Montreal Protocol Protects The Terrestrial Carbon Sink is published in the journal Nature.