Ozone recovery helps reduce global warming

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The recovery of the ozone layer is helping the planet avoid 2.5C of potential warming, in a sign of the impact of curbing ozone-destroying chemicals.

The climate benefits of the global ban on chlorofluorocarbons, which were restricted by the 1987 Montreal Protocol, are greater than previously believed, according to research published in Nature on Wednesday.

The ozone layer in the stratosphere has started to recover as a result of the ban on CFCs, reversing years of thinning.

The study modelled what the earth would look like if CFCs had continued to be used, and found that by the year 2100 the resulting ozone depletion would have caused extensive damage to vegetation due to ultraviolet radiation.

This damaged vegetation would not absorb as much carbon dioxide from the atmosphere, meaning that natural “sinks” from carbon dioxide would be diminished, and more carbon dioxide would be in the atmosphere.

“We found that in this world, without the Montreal Protocol, CO2 levels are 30 per cent higher than in a world where CFCs are controlled,” said Paul Young, lead author of the study and an atmospheric scientist at Lancaster University.

The world has warmed about 1.2C since pre-industrial times, largely due to the increase of carbon dioxide concentrations in the atmosphere, along with other greenhouse gases such as methane.

At the same time, serious depletion of the stratospheric ozone layer has been observed since the 1980s, which allows harmful UV rays to reach the earth’s surface.

The Montreal Protocol is often seen as one of the most successful environmental treaties because it virtually eliminated CFC emissions. Under the treaty, ozone-depleting chemicals were banned in developed countries in 2000 and in developing countries in 2010.

Before the ban, CFCs were commonly found in aerosol sprays, refrigerants and styrofoam packaging.

CFCs are a potent greenhouse gas in their own right, with a warming impact that is thousands of times more powerful than carbon dioxide on a per-molecule basis.

Because of this direct warming impact, eliminating CFCs means avoiding 1.7C of warming by the 2100.

On top of that, the indirect impacts of CFCs in terms of plant damage correspond to about 0.8C of warming by the year 2100, according to the new study, bringing the total avoided warming to 2.5C.

In a world without CFC controls, about 580bn fewer tonnes of carbon dioxide would be stored in vegetation by 2100 — the equivalent of more than 10 years’ of emissions at today’s rates.

However, controlling CFCs was simpler than controlling carbon dioxide emissions, Young said, because CFCs could be easily substituted by other chemicals.

“The world acted and responded to that warning, and avoided a world that would have been pretty devastatingly awful,” said Young. “The hope is we can do something similar with climate. It just won’t be that easy.”