Beware climate change risk from aircon, fridge gases-UN

* Gases that keep us cool risk heating up planet -report

* Developing nations fuelling demand for aircons, fridges

* Alternative climate-friendly gases exist, need development

By David Fogarty

SINGAPORE, Nov 21 (Reuters) - Soaring use of man-made gases used in refrigerators, airconditioners and fire extinguishers risks speeding up global warming and industry should adopt alternatives, a U.N. report said on Monday.

In the most dire forecast, unless governments and industry act to limit the growth, the annual emissions of hydrofluorocarbons, or HFCs, by 2050 could equate to pumping nearly 9 billion tonnes of carbon dioxide into the atmosphere -- about a third of mankind's CO2 emissions now.

HFCs have been phased in since the 1990s to replace chlorofluorocarbons (CFCs), which have damaged the Earth's protective ozone layer and are also very powerful greenhouse gases.

On average, HFCs survive in the atmosphere for 15 years and are about 1,600 times more potent in trapping heat in the air than CO2, underscoring growing alarm about these compounds.

Combined with rapidly growing CO2 emissions from fossil fuels, this will make it even harder for mankind to try to limit global warming to 2 degrees Celsius -- a threshold that risks dangerous climate change, scientists say.