Fugitive methane emissions are often overstated
Opponents of shale gas often argue that it's worse than coal in electricity generation when you account for all the methane (that's the primary component of natural gas) that leaks. They point to a particular study in the US to back up this claim.
In reality, somewhere around 11% of the gas that's extracted would have to leak for it to be worse than coal according to the Government's advisers, the Committee on Climate Change. That's an implausibly large quantity when you consider that it's a valuable product and it's therefore not in anyone's commercial interests to let that much of it escape - according to a 2013 report by the Institute of Directors, a single shale gas well is expected to yield 32 million Therms of gas over its lifetime, which at today's wholesale gas price would be worth £12.5 million; it's hard to imagine a fracking company wastefully letting £1.37 million worth of gas just leak into the sky when they could capture it and sell it to us instead.
Not only that but legislation such as the Dangerous Substances and Explosive Atmospheres Regulations (DSEAR) require companies to plan and conduct their operations so that there are no leaks.
Don't forget also that when coal is mined, it too releases methane into the air - but capturing it, especially from surface mines, is very difficult and so nobody bothers.
Fugitive emissions of shale gas are not going to be the problem that some claim.