Plugging the ozone hole cut global warming too -

Global warming would be much worse if the world had not put a halt to the destruction of the ozone hole above Antarctica, say researchers.

They say the 1987 Montreal protocol, which restricts the use of CFCs and other ozone-depleting chemicals, will cut warming by five or six times more than the Kyoto protocol.

Previous research has shown the ozone layer is recovering and the protocol was hailed by Kofi Annan, former secretary general of the UN, as "perhaps the single most successful international agreement to date".

At the time, it was known that ozone-depleting halocarbons (which include CFCs) were also greenhouse gases and therefore were contributing to warming the atmosphere. What was not known was how much the cooling effect of phasing out these chemicals would add to the cooling effect of patching up the ozone hole in the stratosphere.

The new study, led by Guus Velders of the Netherlands Environmental Assessment Agency, calculated that effect: "It was quite a surprise to see it was so large."

Gigatonnes of carbon

The 2007 assessment of the Intergovernmental Panel on Climate Change estimates that stratospheric ozone has a cooling effect of 0.05 Watts per square metre and that the halocarbons currently in the atmosphere have a warming effect of 0.34 W/m².

Velders and his colleagues used computer models to simulate how the planet would have warmed had it not been for the Montreal protocol. They conclude the warming caused by halocarbons would be nearly twice that currently seen, i.e. between 0.60 and 0.65 W/m².

Another way quantifying the effect is to compare it to the amount of carbon dioxide that would have had the same effect. By 2010, the researchers calculate, the Montreal protocol will have avoided the equivalent of between 9.7 and 12.5 gigatonnes of CO₂ being pumped into the atmosphere every year. In contrast, Velders calculates that if all countries were meet their Kyoto targets by 2012, this will have avoided the equivalent of 2.0 gigatonnes of CO₂ every year.

Rapid growth

"The gases that were regulated by the Montreal protocol were growing very rapidly in the atmosphere, so there was clearly potential for very significant contribution" by limiting them, agrees John Pyle, an atmospheric scientist at the University of Cambridge, UK.

Although the Montreal protocol limited the production of ozone-depleting chemicals, it did not require the removal of equipment containing the gases - refrigerators and air conditioners built before 2000, for instance. Furthermore, some of the chemicals which have replaced CFCs as a result of the Montreal protocol are also greenhouse gases.

Velders says that removing existing equipment that emit CFCs from circulation and replacing "intermediate substitutes" with chemicals that neither deplete the ozone nor warm the planet, would remove the equivalent of a further 1.2 gigatonnes of CO₂ per year. That would be more than half the impact of Kyoto.

Climate Change - Want to know more about global warming - the science, impacts and political debate? Visit our continually updated special report.

Journal reference: Proceedings of the National Aca