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Grim Surprise New Scientist 7 Feb 98

A PREVIOUSLY unnoticed greenhouse gas with a global warming potency 10 000 times that of carbon dioxide may force governments to revise their plans to combat climate change. The chemical is fluoroform (HFC-23), a waste byproduct of the manufacture of HCFC-22, which is widely used in reftigerators and is also a greenhouse gas. Stuart Penkett of the University of East Anglia in Norwich and colleagues reveal in Geophysical Research Letters (vol 25, p 35) that there are 135,000 tonnes of fluoroform circulating in the atmosphere, and that the volume is increasing by 5 per cent a year. The current volume in the air, says Penkett, 'has the global warming potential of 1.6 billion tonnes of carbon dioxide", or three times the annual CO2 emissions in Britain. The researchers say that fluoroform is the most abundant of a group of gases known as hydrofluorocarbons (HFCs), which were placed under international control for the first time at the Kyoto climate conference in December. The finding wiII force countries to consider whether they wiII have to control emissions of fluoroform in order to meet international targets for HFCS. "Collectively, HFCs have quite a lot of potential to cause climate change, partly because they persist in the atmosphere for a long time," says Penkett. Fluoroform is estimated to last 260 years before breaking down. The researchers made their discovery when they reanalysed an archive of air collected over the past 20 years at Cape Grim on the northwestern coast of Tasmania.

Cape Grim is the best-placed site in the world for detecting background levels of gases in the atmosphere. Winds reach the Cape after a long ocean voyage, more than halfway round the world, from Argentina. Releases of fluoroform have soared in recent years as chemicals manufacturers have switched to using HCFC-22 as a substitute for ozone-eating CFCs in fridges and air conditioning systems. HCFC-22 is also used in the manufacture of fluoropolymers, whose uses range from lubricating computer discs to sealing fuel pipes in aircraft. Fluoroform itself is used in small amounts in the production of semiconductors. Fred Pearce