Brantley and Meyendorff give a short history of hydraulic fracturing (fracking), beginning in 1940 with vertical drilling of mostly porous sandstone and limestone formations. The addition of horizontal drilling in the 1990s led to the current boom in shale gas production.
From the onset, they state the cons of fracking - from a local and global perspective.
There is no doubt that natural gas extraction does sometimes have negative consequences for the local environment in which it takes place, as does all fossil fuel extraction. And because fracking allows us to put a previously inaccessible reservoir of carbon from beneath our feet into the atmosphere, it also contributes to global climate change.
The fracking cocktail includes acids, detergents and poisons that are not regulated by federal laws but can be problematic if they seep into drinking water. Fracking since the 1990s has used greater volumes of cocktail-laden water, injected at higher pressures. Methane gas can escape into the environment out of any gas well, creating the real though remote possibility of dangerous explosions.
Pennsylvania is arguably the state with the most experience in fracking, located in the heart of the gas-rich "Marcellus shale, a geological formation that could contain nearly 500 trillion cubic feet of gas — enough to power all American homes for 50 years at recent rates of residential use." So, what has been their experience?
The Pennsylvania experience with water contamination is also instructive. In Pennsylvania, shale gas is accessed at depths of thousands of feet while drinking water is extracted from depths of only hundreds of feet. Nowhere in the state have fracking compounds injected at depth been shown to contaminate drinking water.
The authors cite specific studies of private wells, "trucking and storage accidents", contamination that needed to be addressed, and make it apparent that additional regulations, such as requiring companies to "disclose the composition of all fracking and drilling compounds" would be helpful. They also cite successes in new regulations - such as recycling of briny water to frack more shale.
In sum, the experience of fracking in Pennsylvania has led to industry practices that mitigate the effect of drilling and fracking on the local environment.
While fracking does pose threats to the environment, particularly when there are few regulations of the activity, it should be compared to environmental impacts from other energy sources, such as coal which emits twice as much carbon dioxide per energy unit, in addition to many of toxins such as mercury, as well as waste coal ash - responsible for one of the worst environmental disasters in the U.S.
Last month The Guardian reported that "(t)he explosion of natural gas production, thanks to fracking" that replaced coal power plants contributed largely to U.S. carbon emissions falling to the lowest levels since 1994. On March 13, Bloomberg News reported on a study from Exxon Mobil that "because of a 'pronounced shift away from coal in favor of less- carbon-intensive fuels such as natural gas', carbon-dioxide emissions in 2040 will fall to levels last seen in the 1970s."
The situation is reversed in Europe - with increased coal burning replacing carbon-free, nuclear power, resulting in increased carbon emissions.
The authors conclude by warning that "if fracked gas merely displaces efforts to develop cleaner, non-carbon, energy sources without decreasing reliance on coal, the doom and gloom of more rapid global climate change will be realized."
In short - they appear to endorse what Ernest Moniz, President Obama's choice to be the next Energy Secretary, wrote - that "Natural Gas Could Serve as 'Bridge' Fuel to Low-Carbon Future".