Shale gas worse for climate than coal

Shale gas, hailed by many as the transition fuel on route to a low-carbon future, could be worse for the climate than coal, according to a new study.

Natural gas, produced from shale rocks, using the controversial hydraulic fracturing (“fracking”) process, has been “part of the vision” due to the large amounts available as conventional natural gas resources deplete.

But researchers from the US have found that this process could be more harmful, in terms of climate change, than other natural gas and also coal, due to the amount of methane – a more harmful greenhouse gas than CO2 – emitted in the process.

They say this “undercuts the logic of its use” as a steeping-stone fuel.

Robert Howarth, report author said: “It is the first comprehensive analysis of the greenhouse gas footprint of shale gas, and it casts doubt on the conventional wisdom that this should be viewed as a transitional fuel over coming decades.  The greenhouse gas footprint of shale gas is at least as bad as that of coal, and quite likely worse.”

While the burning of shale gas produces less carbon dioxide than coal, much more methane is released in the process of extracting the gas, than that emitted during coal mining.

Methane is a more potent greenhouse gas than carbon dioxide, but has a shorter residence time in the atmosphere. As a result its effect on global warming falls more rapidly.

The research, published in Climatic Change, said: “Compared to coal, the footprint of shale gas is at least 20 per cent greater and perhaps twice as great on the 20 year horizon and is comparable over 100 years.”

It also found that the greenhouse gas footprint of shale gas is at least 50 per cent greater than for oil, for the 20-year horizon and similar or 35 per cent greater over 100 years.

Between 3.6 per cent and 7.9 per cent of methane from the shale gas production escapes to the atmosphere in venting and leaks, as well as with flow-back return fluids during drilling, according to report authors from Cornell University in New York.

These fluids occur from the large amounts of water used in the process of hydraulic fracturing, where they are forced under pressure into the shale rock, fracturing it. A significant among of this water returns to the surface, accompanied by large quantities of methane.

Routine production and downstream methane emissions are also large, but comparable to those of conventional gas.

The research only takes account of emissions during ‘best practice’ operations. If industry does not operate under ‘best practice’ the impact of shale gas could be even worse than the research predicts.

While Robert Howarth believes legislation, is achievable and could limit the damage of shale gas, but he is not overly optimistic.

He said: “The low end estimate reflects use of best practise, although perhaps the industry can do even better than that, if forced to do so, perhaps getting down to as low as even 2 to 2.5%.  That would be expensive, though, and would still represent a significant greenhouse gas footprint.  And to date, industry has strongly resisted regulation.”

With shale gas becoming the hot choice as a transition fuel; allowing for continued reliance on fossil fuels in the short term while reducing global emissions, this report calls into questions its use as a ‘climate friendly’ alternative.

Howarth, and co-authors stress that while the full footprint should be used when considering alternative energy futures, they do not intend the study to justify continued use of either oil or coal.