Dr. Thorsten Warneke discusses the following scientific papers by Howarth, R.W. (2014) and Heath et al (2014)

Two recent articles come to different conclusions regarding the impact of shale gas on climate. Natural gas is generally considered to be climate-friendlier than coal and oil. The reason is that natural gas emits less carbon dioxide than coal or oil. However, methane is a very potent greenhouse gas, and is the main constituent of natural gas; methane leakage during the life cycle of natural gas can potentially negate the climate benefits of natural gas compared to coal. It has been estimated that natural gas has a climate benefit compared to coal only if leakage rates are smaller than roughly 3% (Alvarez et al. estimated 3.2%, but this number has to be revised using the up-to-date global warming potentials of methane).

An article by Heath et al. harmonizes estimates of shale gas life cycle greenhouse gas emissions for electric power generation. Essentially they review existing literature on natural gas life-cycle greenhouse gas emissions and make the results comparable. Their main conclusions are that shale gas and conventionally produced natural gas have similar greenhouse gas emissions, which are approximately half of those from coal.
A second article by Howarth concludes that the life-cycle greenhouse gas emissions for natural gas are greater than those of coal or oil.

How is it that two studies with very different conclusions on the climate impact of natural gas have been published? The reason is that not enough data exist on natural gas life-cycle greenhouse gas emissions to make an ultimate conclusion. The study by Heath et al. mainly compiles estimates of greenhouse gas emissions from studies before 2012, which rely on the knowledge of greenhouse gas emissions during that time, whereas Howarth’s conclusion is based on recent studies that report large methane emissions from areas where natural gas is produced. These studies have not been considered by Heath et al. Neither of these recent studies provide sufficient evidence for a final conclusion for two reasons: either the emissions are given for large spatial areas where one cannot necessarily attribute the emissions uniquely to natural gas, or measurements are conducted on small spatial and temporal scales and it is uncertain to what extent these measurements can be extrapolated.

With an increasing number of measurements being taken over the next few years, a more robust estimate of lifecycle methane emissions from natural gas will be possible, but currently it is an open scientific question. One other point where the two studies differ is the time period considered for the warming potential. This is important because the shorter the time period, the higher the warming potential of methane compared to carbon dioxide. It would be better if future studies would consider several time scales, because of the importance for feedback in the climate system.