Their new evidence reveals the planet’s critical ability to absorb carbon from the atmosphere could have been massively degraded sending global temperatures soaring if we still used ozone-destroying chemicals such as CFCs.

New modelling by the international team of scientists, including Dr Anna Harper from the University of Exeter, paints a dramatic vision of a scorched planet Earth without the Montreal Protocol, what they call the “World Avoided”.

The study, published in Nature, draws a new stark link between two major environmental concerns – the hole in the ozone layer and global warming.

The research revealed that if ozone-destroying chemicals had been left unchecked, then their continued and increased use would have contributed to global air temperatures rising by an additional 2.5°C by the end of this century.

Their findings show that banning CFCs has protected the climate in two ways – curbing their greenhouse effect and, by protecting the ozone layer, shielding plants from damaging increases in ultraviolet radiation (UV). Critically, this has protected plant’s ability to soak up and lock in carbon dioxide from the atmosphere and so prevented a further acceleration of climate change.

The research team developed a new modelling framework, bringing together data on ozone depletion, plant damage by increased UV, the carbon cycle and climate change.

Their novel framework investigating an alternative future of the planet where the use of CFCs continued to grow by around three per cent a year showed:

• Continued growth in CFCs would have led to a worldwide collapse in the ozone layer by the 2040s.
• By 2100 there would have been 60 per cent less ozone above the tropics. This depletion above the tropics would have been worse than was ever observed in the hole that formed above the Antarctic.
• By 2050 the strength of the UV from the sun in the mid-latitudes, which includes most of Europe including the UK, the United States and central Asia, would be stronger than the present day tropics.

The researchers’ models show that in a world without the Montreal Protocol the amount of carbon absorbed by plants, trees and soils dramatically plummets over this century. With less carbon in plants and soils, more of it remains in the atmosphere as CO₂.

Overall, by the end of this century without the Montreal Protocol CFC ban there would have been 580 billion tonnes less carbon stored in forests, other vegetation and soils; and an additional 165-215 parts per million of CO₂ in the atmosphere – an additional 40-50%; and the huge amount of additional CO₂ would have contributed to an additional 0.8°C of warming through its greenhouse effect.

Ozone depleting substances, such as CFCs, are also potent greenhouse gases and previous research has shown that their ban prevented their contribution to global warming through their greenhouse effect.

By the end of this century, their greenhouse effect alone would have contributed an additional 1.7°C global warming. This is in addition to the newly quantified 0.8°C warming, coming from the extra CO₂ that would have resulted from damaged vegetation, meaning that temperatures would have risen 2.5°C overall.

Dr Paul Young, lead author from Lancaster University, said: “Our new modelling tools have allowed us to investigate the scorched Earth that could have resulted without the Montreal Protocol’s ban on ozone depleting substances.

“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. 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.”

 ‘The Montreal Protocol protects the terrestrial carbon sink’ is published in Nature on Wednesday, August 18^th 2021.