climate change global warming

Global warming would be 2.5°C higher without 1980s CFC ban, study finds

New evidence suggests that 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.

The Montreal Protocol was signed by 197 countries in 1987 to ban the production of numerous substances that are responsible for ozone depletion.

Without the global ban, we would already be facing the reality of a ‘scorched earth’, according to an international team of scientists from the UK, USA and New Zealand.

They said that if ozone-destroying chemicals had been left unchecked, 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.

The ban has protected the climate in two ways, by curbing their greenhouse effect and by protecting the ozone layer which shields plants from damaging increases in ultraviolet radiation (UV). This has protected plants' ability to soak up and lock in carbon dioxide from the atmosphere and so prevent 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. It shows an alternative future of a planet where the use of CFCs continued to grow by around three per cent a year.

It suggests that continued growth in CFCs would have led to a worldwide collapse in the ozone layer by the 2040s and 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 depleted ozone layer would have seen the planet, and its vegetation, exposed to far more of the sun’s UV.

Plants absorb carbon dioxide (CO2) through photosynthesis and studies have shown that large increases in UV can restrict plant growth, damaging their tissues, and impairing their ability to undertake photosynthesis and therefore absorbing less carbon.

Less carbon in vegetation also results in less carbon becoming locked into soils, which is what happens to a lot of plant matter after it dies. All of this would have happened on a global scale.

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.

Without the Montreal Protocol it is believed there would be an additional 165-215 parts per million of CO2 in the atmosphere, depending on the future scenario of fossil fuel emissions, compared to today’s 420 parts per million CO2 contributing 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.”

An MIT study last year found that old equipment such as building insulation foam, refrigerators and cooling systems that were manufactured before the Montreal Protocol are still leaking CFCs into the atmosphere.

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