Financial Times, 7 March 2016:
Robin Russell-Jones (Letters, March 4) argues that fugitive emissions of methane from gas production remove the global warming advantage of natural gas over coal. Recent published studies and our own measurements suggest a more nuanced view. Methane leaks from gas production are typically over 1 per cent, as Dr Russell-Jones states, but coal mining also emits methane. Our own work measuring carbon isotopes in methane in air from China in winter suggests coal is an important contributor to East Asian methane.
Turning to shale gas, Dr Russell-Jones suggests methane losses average 8 per cent of production, with an upper limit of 13 per cent. This contrasts with the meticulous work of the US National Oceans and Atmospheric Administration (NOAA) and the US Environmental Defense Fund. In Utah’s small Uintah basin, high leakage was indeed measured, but in the major Barnett Shale basin in Texas, methane emissions attributed to fossil sources were 1.3-1.9 per cent of production. Gas-fired electricity in this region would cause less climate forcing than coal-fired. A few “high emitters”, for example in storage and collection systems, have a disproportionate impact. Our own work in the UK and Australia similarly shows the importance of high emitters, that our mobile vehicle-mounted analyser easily pinpoints. These sites presumably represent financial loss and safety risks, and should relatively easily be controlled.
The focus on fracking distracts attention from the remarkable global methane rise since 2007, exceptionally strong in 2014 and 2015, which seems mainly to be from tropical sources. The rise has been accompanied by a carbon isotopic shift that suggests the increase is not primarily from fossil fuels but from tropical wetlands responding to meteorological events. Is this the result of a large but “normal” decadal-scale weather oscillation, or is methane the canary that warns a profound tropical change is occurring? We simply do not know. Tracking tropical emissions depends on a very few remote marine sites. Satellite data are not accurate enough, nor can they use isotopes to identify sources. Our instrument on Ascension Island has recently failed, and is so old that the manufacturer is soon withdrawing service support. Ascension’s air integrates a wide tract of the Southern Hemisphere: for want of £5,000 we risk losing the 2016 record of methane and CO2 during the current great El Niño. Many of our international partners in greenhouse gas measurement are suffering similar budget challenges. This illustrates a wider point: the greenhouse debate is like an inverted pyramid, with a vast top layer of opinion interpreting underlying computer models, that in turn depend on a tiny basis of direct in situ greenhouse gas measurement.
Dr Euan G Nisbet
University of London, UK