What is “bad” or “ugly” about natural gas? The worst problem with natural gas is that it still produces CO2 when it burns, even though only about half as much as burning coal. However, the EPA recently evaluated the greenhouse gas emissions from natural gas and concluded that, because of leaks from pipes and venting from gas wells, natural gas may actually be only about 25% cleaner than coal, not 50%

(32) . Another “bad” is that methane is a greenhouse gas in its own right. In fact, it is 26 times more effective than CO2 as a greenhouse gas, but it rapidly breaks down in the atmosphere into CO2 and water, with a lifetime of 12 years. Greenhouse gases are compared by their global warming potential (GWP)—a relative number that compares their effectiveness to CO2 over a specified number of years. The GWP of methane is 72 over 20 years and 25 over 100 years (see Appendix A). Methane emis­sions accounted for 11.6% of the greenhouse gas GWP in the United States in 2010

(33) . About 41% of methane emissions come from energy production, 30% from agriculture (mostly cattle), and 28% from landfills and waste management (34).

According to EPA estimates, 570 billion cubic feet of methane leaked from pipes or were vented from natural gas wells and the natural gas distribution net­work in 2009. That represents 2.4% of the total US natural gas production for 2009 (35). The National Oceanic and Atmospheric Administration (NOAA) and the University of Colorado recently measured daily methane emissions over three years from the Denver-Julesburg Basin due to fracking and concluded that about 4% (range of 2.3-7.7%) of the natural gas is lost to the air (36). This is an even larger loss than that estimated by the EPA and does not include additional losses in pipelines and the distribution network. Robert Howarth and colleagues from Cornell University analyzed the losses of methane from natural gas well develop­ment (“fugitive emissions”) and estimated that 3.6-7.9% of the lifetime produc­tion of the well is lost through fugitive emissions (37). Since methane is such an efficient greenhouse gas, this loss nullifies much of the advantage of natural gas over coal (38). The authors conclude that “[c]ompared to coal, the footprint of shale gas is at least 20% greater and perhaps more than twice as great on the 20-year horizon and is comparable when compared over 100 years.” How true that statement is depends greatly on the actual percentage of natural gas that is leaked and on the total amount of natural gas produced.

Ramon Alvarez and colleagues analyzed how long it would take to get a net climate benefit from using natural gas instead of coal in a power plant, and the answer depends greatly on the percent of natural gas leakage. At a leakage rate of 3.2%, they calculate that there would be an immediate global warming benefit in converting from coal to natural gas power plants. However, if the leakage rate were 5%, it would take over 40 years for a benefit (35). Clearly, it is important to get more precise information on the actual leakage from the natural gas produc­tion system but even more important to take steps to reduce the fugitive emissions wherever possible.