One of the justifications for fracking is the use of natural gas as a bridging fuel between coal and a low-carbon future. However natural gas is mostly methane, which has strong global warming impacts in its own right. Natural gas therefore only provides climate benefits over coal if the leakage is no more than 2-3%.
We cannot measure leaks from every pipe joint. One alternative is to measure the sum of lots of leaks from a distance. Flights over US shale gas fields reveal large methane sources, but these areas also have cattle farms that produce methane and the two sources need to be separated.