If the world hadn't come together to ban ozone-destroying chemicals in the late 1980s, a new study suggests climate change would have drastically worsened global warming by the 2040s.
The models paint a picture of a world avoided – a scorched Earth scenario even more fiery than the climate crisis we currently face.
According to the results, a continued surge in chlorofluorocarbons (CFCs) would have caused the ozone layer to collapse worldwide by the 2040s, leading to a rise in harmful ultraviolet radiation showering upon plants and animals.
Without the worldwide agreement to ban these chemicals, known as the Montreal Protocol, researchers think the tropics would have lost 60 percent of their ozone coverage by 2100 – a hole even bigger than the one that formed over Antarctica in the early 1980s.
In all likelihood, such mass exposure to unfiltered radiation would damage plant tissues, dramatically slowing their growth and impairing their ability to photosynthesize in numerous parts of the world – some more than others.
By 2100, researchers estimate the ozone's collapse from CFCs would ultimately have stopped forests, soils, and other vegetation from absorbing 580 billion tonnes of carbon dioxide, making its concentration in the atmosphere 40 to 50 percent higher.
That's an extra 0.8 °C (1.4 °F) of warming come the end of the century, and that's just from a leak in the carbon sink. CFCs themselves are greenhouse gases, and if we hadn't banned them when we did, researchers predict they would have contributed an additional 1.7 °C (3 °F) global warming by 2100.
In total, that's 2.5 °C (4.5 °F) of warming that we managed to avoid through sticking to the Montreal Protocol. When you consider that today we are trying to curb our fossil fuel emissions to keep warming well below 2 °C, that's not a bullet we've dodged, it's a bazooka.
The result is that today we actually have a chance to stop the worst effects of climate change. Sure, we're on the brink of unleashing a 'hothouse Earth', but if it weren't for the Montreal Protocol, we could have been looking forward to a downright scorched one.
"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," says Paul Young from Lancaster University.
"The increased UV would have massively stunted the ability of plants to soak up carbon from the atmosphere, meaning higher CO2 levels and more global warming."
Still, that doesn't mean we're in the clear. The world has a lot of work to do to turn our fossil fuel emissions around, and at the same time, we can't get complacent about CFCs.
While the results of this recent research speak to the success of the Montreal Protocol, they also hint at its possible failures.
If the agreement is one day to fall into disregard, it could ultimately undermine our chance to mitigate the climate crisis.
A few years ago, however, scientists chanced upon a mysterious source of CFCs that seemed to be on the rise. Later, the emissions appeared to be coming from the mainland of China, in a highly industrial area that was probably producing the chemical illegally or possibly evening unknowingly.
Regardless, its presence triggered renewed warnings to not forget the Montreal Protocol and what can be achieved when the world sets its collective mind to a task.
The study was published in Nature.