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 UN 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.

“In the future, HFC emissions have the potential to become very large. This is primarily due to growing demand in emerging economies and increasing populations,” said the report by the UN Environment Programme released in Bali, Indonesia.

New middle-class consumers in major developing countries such as China, India, Brazil and Indonesia are driving demand for new refrigerators and airconditioners. HFCs are also used to make insulating foams and aerosols.

A global pact called the Montreal Protocol, widely regarded as one of the world’s most successful environmental treaties, led nations to phase out CFCs from the late 1980s.

Production quickly plunged, cutting the equivalent of billions of tonnes of CO2 annually.

HFCs do not damage the ozone layer, which shields the planet from cancer-causing ultra-violet radiation.

Global consumption has doubled in a decade to just over 400,000 tonnes in 2010 and consumption of some HFCs is growing 10 percent a year, threatening to undo the climate benefits of the Montreal Protocol.

“If HFC emissions continue to increase, they are likely to have a noticeable influence on the climate system,” said the report, released during a meeting of Montreal Protocol signatories.

There are options, though. These include developing and ramping up production of HFCs that survive only a matter of days in the atmosphere or using different gases altogether to chill food and drinks or keep the car cool on a hot day.

For example, some manufacturers are already using hydrocarbons, CO2 and ammonia for industrial refrigeration and airconditioning plants while fire-fighting systems can use foams, dry chemicals and inert gases. Increasingly, household refrigerators are using hydrocarbons in compressors, the report says.

But more work needs to be done on developing and phasing in new alternatives and working out the long-term benefits to ensure they don’t damage the climate or have other side-effects.