"A group of chemicals called  hydrofluorocarbons, long hailed as a substitute for gases that can destroy the ozone layer, are now seen as a growing greenhouse threat given their outsize ability to warm the atmosphere.

The chemicals, mainly referred to by the acronym  HFC's, have long been known to be potent heat-trapping substances. But because they are released in tiny traces, they currently contribute less than 1 percent of the climate-warming effect from human-generated carbon dioxide.

But fast-paced growth in the use of these chemicals as refrigerants and in air conditioning in developing countries is poised to make HFC's a far bigger contributor to warming, scientists are saying. A sobering new analysis of HFC emission trends, published Monday in the Proceedings of the National Academy of Sciences, forecasts that by midcentury, emissions of these chemicals could be heating the atmosphere with the same punch as 7 or 8 billion tons a year of carbon dioxide. (For comparison, the total annual global emissions of carbon dioxide top 30 billion tons a year now."

Andrew C. Revkin reports in Dot Earth June 22, 2009. [2]