Your correspondent David England does a disservice to the anti-fracking cause (Shale gas promises could be hot air, 2 July). He says that methane is 200% worse than carbon dioxide as a global warming gas – the correct figure is 2,000%. This means that a small leak from fracking wells will more than cancel out the so-called gain by using gas rather than coal.
Each molecule of methane is approximately 60 times more effective as a greenhouse gas than a molecule of carbon dioxide. But, over time, methane is very slowly converted to carbon dioxide through oxidation processes in the atmosphere. Averaged over 100 years, this makes methane about 20 times more potent as a greenhouse gas than carbon dioxide, that is, about 2,000% worse than carbon dioxide.
A research group at Cornell University has shown that it requires only 4-5% leakage from fracking wells to cancel out the gain from using gas rather than coal.
Dr David Hookes
Liverpool
