Methane leakage from US shale gas fracking means reported falls in US emissions may be exaggerated, according to an analysis by Energydesk.
Earlier this year, the world’s leading authority on energy, the International Energy Agency (IEA) announced that the US’s CO2 emissions had fallen in 2011 by 2% (92 Mt), but it’s analysis excludes fugitive emissions from fracking.
The IEA attributed the fall to the switch from coal to less polluting gas power, a success in tackling climate change widely cited by policy-makers including the UK government’s energy advisor, Professor Helm.
But as Energydesk reported earlier this year increased use of renewables, not gas, accounted for most of that change, with gas accounting for just 19Mt of CO2 reductions.
And research by Energydesk suggests that the switch from conventional to shale gas in the US power sector may actually have driven emissions up - you can see our analysis here.
Fugitive emissions
Fracking involves pumping water and chemicals at high pressure into the shale rocks to crack them open and release gas. Depending on how it is carried out this process can release gas which is not captured but the amount varies from well to well.
Some studies suggest that industry measures to prevent leakage mean that it is minimal and that there is therefore very little difference between gas from shale and from conventional sources - in which case this analysis is unnecessary.
It is doubtless very hard to know for sure how much methane is leaked from the average fracked well, especially in the absence of atmospheric data. This analysis uses a range of estimates broadly consistent with some recent field measurements which produced results at the higher end of the range.
Although methane is a stronger greenhouse gas than CO2 it breaks down in the atmosphere quickly. This means the Global Warming Potential of methane is larger over a 20 year timescale than over a 100 year timescale - so we’ve looked at both.
Increased emissions
The use of shale gas for power in the US has been increasing.
In 2011 a total of 1016 billion kW/h of energy was used by the burning of natural gas; a third of which was supplied by shale gas.
Based on our range that means that 53, 89 or 201 Mt of CO2 equivalent is released when the leaked emissions are accounted for over 20 years and 13, 33 or 67MT over 100 years.
This would nearly completely cancel out the 92 Mt reduction in US emissions over a 20 year period.
Even 100 years after the emissions we would most likely still be experiencing over a third of the emissions reportedly saved.
That doesn’t mean gas from shale is more polluting than coal, it may be - the numbers on that again vary - but it does suggest that the reported data on US emissions portrays a potentially misleading impression of it’s success in tackling climate change.
In it’s Golden Rules for the Golden age of gas the IEA outlines procedures to limit emissions from shale. The ability of gas from shale to play a role in reducing emissions will depend on them being applied successfully.
