Fugitive (or unburned) methane emissions
Although natural gas burns much cleaner than coal and oil, and produces about half the CO2 emissions at the stack compared to coal, it has two properties that give us cause for concern: first, it has a tendency to leak and escape into the atmosphere unburned as “fugitive emissions.” Although controlling fugitive emissions is possible, they tend to occur at all phases of the life cycle from extraction to distribution and storage right up to the point of combustion.
Second, molecule for molecule CH4 has a much greater global warming potential (GWP) than CO2, but that number changes over time due to the varied propensities of the two molecules to persist in the atmosphere over time. The number used to describe the GWP difference between the two often is 25x, which means that CH4 is 25 times more potent than CO2. That number, however, is for a 100-year time frame.
(CC Image of fracking in process by Joshua Doubek (Own work) [CC-BY-SA-3.0 (http://creativecommons.org/licenses/by-sa/3.0)], via Wikimedia Commons)
The difference over 20 years, however, may be more than 100x. Because climate change looms so large, some authorities argue that the shorter time period should be used. Either way, the benefits associated with natural gas over coal decrease with increasing amounts of fugitive emissions. Moreover, because the GWP of natural gas is much greater than CO2, a relatively small percentage of leakage can negate or reduce the benefits at the stack.
Additionally, hydraulic fracturing (fracking’s) other environmental impacts including freshwater contamination, freshwater depletion, anthropogenic earthquakes, and habitat destruction should be factored into the accounting as negative externalities. Although most end users, such as college campuses, are not required to include such costs, it is not unreasonable to consider them and to make plans with them in mind.
(CC Image by Enescot (Own work) [CC0], via Wikimedia Commons)