A recent study from the National Academy of Sciences predicts so-called “green” refrigerants that replace ozone-depleting ones will contribute to global warming if left unchecked.

Published last month in the Proceedings of the National Academy of Sciences, the study presents new data about modern hydrofluorocarbons (HFCs), which are considered greenhouse gases. The study claims HFCs could contribute the equivalent of up to 45% of carbon-dioxide emissions by 2050. Under that worst-case scenario, even if countries adopt a 450-ppm cap on CO2, “You still would have overshot it by about 50%,” says Mack McFarland, a scientist at refrigerant maker DuPont and the paper’s co-author.

Use of such HFCs as R-404a, R-410a and R-134a is set to grow as hydrochlorofluorocarbons (HCFCs), such as R-22, phase out under the Montreal Protocol. Ozone-depleting-potential levels in air-conditioning fluids have now dropped to near-zero levels, but their global-warming-potential, while lower than in the past, is still too high to ignore.

Economic growth in established markets, as well as developing ones, such as Asia, are expected to boost HFC use. The paper concludes that the transition away from ozone-depleting fluids “has implications for future climate.” A cap-and-reduction program would help stem growth, McFarland notes, adding that DuPont and others are working on next-generation, low-GWP refrigerants, such as HFO-1234yf.

Starting in January 2010, manufacturers must stop producing R-22 for new equipment, but they may still produce it to service existing units. By January 2020, recycling will still be allowed, but R-22 will be completely banned from production.