Financial Times, 14 March 2016:
Dr Euan Nisbet (Letters, March 7) takes issue with Dr Robin Russell-Jones (Letters, March 4) over the sources of increasing atmospheric methane. Dr Russell-Jones pointed to a review paper which he and I recently presented to the Committee on Climate Change, which shows that fracking in the US has produced such high emissions of methane that natural gas is a worse source of climate-changing gases than coal. Dr Nisbet briefly points to recent research by the US Environmental Defense Fund showing lower emissions in one oil and gasfield in the US, the Barnett Shale, as evidence that our estimate is too high, and goes on to stress the importance of “natural” emissions from tropical sources such as wetlands in Africa.
In fact, both fossil and natural methane emissions have an important bearing on Earth’s future. Concerning fossil methane, the Barnett Shale region does indeed emit less methane than most other unconventional oil and gas producing regions, probably because it is a mature field with a much lower rate of well completions (fracking) than in many other regions. Still, we believe the Environmental Defense Fund paper underestimates Barnett Shale emissions by about 40 per cent owing to its neglect of infrequent emission events of magnitude greater than about 1 tonne per hour, which, because they are rare, could only be picked up by long-term measurements beyond the timeframe of the Fund’s study. The importance of such events is underscored by the recent Aliso Canyon accident in California which emitted methane at the rate of 60 tonnes per hour, equivalent to emissions from an entire gasfield, for a period of several months. Taking into account the best oil and gas methane data currently available, and data from coal production, we concluded that methane emissions from the fracking industry are high enough to reverse the supposed benefit of natural gas over coal, and we stand by that conclusion. This is an absolutely key point for decision makers contemplating the future of energy generation in the UK.
Concerning natural methane sources, it is clear from satellite data that there has been a rise in atmospheric methane emissions at latitudes that intersect the Sahel region of Africa. Industrial activities such as hydroelectric projects, as well as human induced climate change, are damaging the wetland ecosystems of the Niger delta and this is clearly another significant climate threat. I entirely concur with Dr Nisbet on the critical importance of continuous atmospheric monitoring during a period of rapid climate change, and on the value of isotopic measurements. Data, modelling, understanding, and well-informed decision-making are all now vital to our future.
Prof Nick Cowern
Oswaldkirk, N Yorks, UK