The recent interest in greenhouse gas emissions from shale gas, which is extracted in a process commonly known as "fracking", stems from two sources. First, the advent of shale gas fracking in the past five years has greatly changed the energy outlook in the US as well as internationally. It promises to bring substantial new supplies of inexpensive natural gas to the market and thereby change investment opportunities in the energy sector. As such, there is much interest in understanding its implications for US and European energy security, as well as for alternative technologies such as renewables, nuclear and coal.

Second, because of the relative rapidity with which this new resource has come online, there is a sense that its potential negative impacts remain unchecked. Concerns have been raised primarily about the hydraulic fracturing process itself – particularly as to whether the fluids used may pose an environmental hazard, and even whether the process might be linked to increased seismic activity.

Earlier this year, questions were raised about whether methane emissions from the extraction process for shale gas might actually make the overall greenhouse gas impact of this fuel higher than that for, say, coal. Since coal is normally a much more carbon-intensive fuel than gas – nearly 75% more just in terms of carbon dioxide per energy unit – this was a surprising possibility. Indeed, it genuinely called into question the prospect of relying on shale gas as a so-called "bridge fuel" to a low-carbon energy system.

In this study, the authors investigate this question using publicly available data sources on shale gas extraction processes and a few basic scenarios for electricity technologies. Three conclusions are worth noting. Under central assumptions, the researchers estimate that shale gas used for electricity generation will generate around 10% more greenhouse impact than conventional gas would, and that this impact remains substantially lower than the impact of coal-fired electricity (around 55%). The authors also highlight the extreme importance of better data collection and analysis for the methane emissions from the fracturing process – this would enable much greater precision in the assessment of overall impact. And finally, they point out that improvements in extraction technology could reduce the difference in impact further, and that this might be bolstered with some regulatory oversight.