The Howarth et al paper estimating the climatic impact of shale gas extraction by hydraulic fracturing (fracking) has provoked a number of responses across the media. Since the issue of natural gas vs. coal or oil, and the specifics of fracking itself are established and growing public issues, most commentary has served to bolster any particular commenter’s prior position on some aspect of this. So far, so unsurprising. However, one aspect of the Howarth study uses work that I’ve been involved in to better estimate the indirect effects of short-lived emissions (including methane, the dominant component of shale gas). Seeing how this specific piece of science is being brought into a policy debate is rather interesting.
The basic issue is that for any real economic or industrial activity there are a variety of emissions associated with the life cycle of that activity – from construction, transport of fuels, operating emissions, end products etc. In deciding whether one activity is ‘better’ or ‘worse’ than an alternative, people need to have an assessment of the cost, the carbon footprint, other impacts etc., over that whole life cycle. There are of course different elements to this (cost, pollution, social issues) that need to weighed up, but one piece that is amenable to scientific analysis is the impact on climate drivers.
Calculating the net climate impact of an activity requires tracking many different emissions (not just CO2), and accounting for their (time-varying) impact on radiatively active components of the atmosphere or the properties of the affected land surface. While straightforward in conception, this can be complex and, inevitably, there are uncertainties in assessing all the knock-on effects. Over the years, many of the complexities have become better acknowledged which, in some cases, increases the total uncertainty, but the alternative of assuming that the indirect effects have zero impact with zero uncertainty is not tenable.