.In a recent review, DECC concluded that emissions from UK shale

gas should be comparable with conventional gas and lower than

coal (Figure 3). However, it excludes post-production emissions,

which may be considerable. For example, a recent academic

study found that groundwater methane concentrations increased

as shale gas wells aged, indicating significant leakage77. The

DECC review also assumes methane to be just 25 times more

potent a greenhouse gas than CO2, based on the 100-year

timeframe previously recommended by the IPCC78. However, the

IPCC now estimates methane to be 34 times more potent, or 84-

86 times when assessed over a 20-year timeframe (accelerating

warming in the short-term)79, meaning that the figures given by

DECC represent a significant underestimate.

To put the fugitive emissions figures into context, it has been

suggested that new gas plants reduce climate impacts compared

with new coal plants only if leakage rates remain below 3.2%81.

This is based on methane being 25 times (not the newly

recommended 34 times) more potent than CO2