The gas boom of the past couple of years is the biggest story on the planet right now, for it is central to whether or not we can halt global warming.

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With the nuclear industry on the back foot after the Fukushima reactor crisis in Japan, natural gas is now being positioned  as the "only realistic" clean energy option. In the last few years, billions have been poured into gas exploration and development - far more than has gone into developing renewables such as solar or wind. Natural gas is is claimed, generates half the greenhouse gas emissions of coal, making it a valuable transition fuel in any strategy to reduce emissions. But is this true? It's a key question, because if the world invests for gas it will inevitably delay the development of low or zero-carbon renewables such as solar and wind. So if gas doesn't lead to a lower-emissions future, we're in big trouble.

As I've blogged before, it's been suggested that if as little as 2 per cent of gas escapes into the atmosphere - called "fugitive emissions" - the global warming impact of gas could be just as bad than coal. That includes leaks during extraction, flaring to burn off excess gas, leaks while the gas is piped to the user, and even in your home - if, say, you turn your stove on then fumble for a match. Maybe it's no accident that figures for gas leakage are almost impossible to find, but some studies suggest it is not far off the 2 per cent mark. One US Enivonmental Protection Agency study put leakage at 3.3 per cent.

The hot new frontier in the fossil fuel world is shale gas, or coal seam gas - gas trapped in layers or earth and rock, including coal seams, and extracted by a process called hydraulic fracturing, or "fracking", which involves cracking open underground rocks to release the trapped gas. China is about to get into shale gas in a big way.

The Guardian has just produced a special report on shale gas.

Last week, SBS screened a documentary about fracking called Gasland, which has also just been released on DVD in Australia. Coal seam gas featured in a recent Four Corners report.

Critics of fracking say it can release methane locally (as well as carcinogenic chemicals used in the extraction process) including into underground aquifers. Gasland shows methane coming out of the kitchen taps of local residents. Maybe that would be a necessary evil if it reduced emissions. But now a new study claims the fugitive emissions from shale gas might make it worse than coal in terms of emissions.

Ironically, within a decade or two solar power is likely to be competitive with coal and gas. But by then gas extraction, along with coal, may have pumped enough greenhouse gases into the atmosphere to set off disastrous feedback mechanisms, such as the release of methane currenly locked into the frozen tundra in northern Siberia and Canada, that would make global warming unstoppable. Far from saving us, going for gas could turn out to be the greatest mistake in history. With stakes this high, we mustn't just take the word  of the gas lobby. Greenhouse emissions from gas must be given the closest scrutiny possible.

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