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“rebound effect” threatens to accelerate the rate of global warming

 
The Montreal Protocol led to a global phase-out of most substances that deplete the ozone layer, such as chlorofluorocarbons (CFCs). A happy side-effect of the gradual ban of these products is that Earth’s climate has also benefited because CFCs are also potent greenhouse gases. However, now a “rebound effect” threatens to accelerate the rate of global warming.

Hydrofluorocarbons (HFCs), which have been used in recent years in increasing quantities as substitutes for CFCs, are also climatically very active and many are also extremely long-lived. In the journal Science an international team of researchers recommends that the most potent of these gases also be regulated. This could save the positive “side effect” of the Montreal Protocol for the global climate.

It is regarded as the most successful international environmental agreement and has, to date, been ratified by 196 countries — the Montreal Protocol on Substances That Deplete the Ozone Layer. As a result, CFCs and ozone “killers” will gradually disappear from the atmosphere over the coming decades. And because many of these substances are also very active greenhouse gases, Earth’s climate will profit from the sinking concentrations too.

So far, so good. In many processes where previously CFCs were used, these are now being increasingly substituted by fluorinated compounds such as HFCs (which, simply put, are similar substances to CFCs but do not contain chlorine and do not deplete stratospheric ozone). They are used as cooling agents in air conditioning plants and refrigerators, as propellants in aerosol cans, as solvents and as foaming agents in the manufacture of foam products. However, there is a downside to the use of HFCs — they are also very potent greenhouse gases. HFC-134a, also known as R-134a, for example, which is used in automobile air conditioning units, is 1430 more active than the “classic” greenhouse gas carbon dioxide (CO2).

International environmental agreements can also have unwanted side effects

The reduction of greenhouse gas emissions is covered by the Kyoto Protocol. This agreement is, however, not binding for the world’s largest emitter of greenhouse gases, the USA (which has never ratified the protocol), nor for threshold and developing countries. In addition the Kyoto Protocol is currently limited to the period from 2000 to 2012. No agreement has yet been reached on extending it. What this means is that the significant increase in global emissions of HFCs seen over the past few years will soon negate the positive effects on climate brought by the Montreal protocol’s CFC phase-out.

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