August 19, 2011
The issue of life cycle analyses of greenhouse gas (GHG) emissions is getting increasing attention as the U.S. moves toward a “cleaner” energy supply. A life cycle analysis refers to the carbon footprint of a particular generating fuel source over its entire production, combustion and disposal cycle, rather than examining only the GHG emissions produced by combusting the fuel to generate electricity. Looking strictly at the GHG emissions produced to generate electricity, for example, natural gas is commonly said to be roughly twice as clean as coal. (By comparison, nuclear, wind and solar are 100 percent “clean” with respect to GHGs produced in generating electricity. Under a life cycle analysis, however, nuclear power is far from “clean,” given the GHG emissions associated with mining and processing the uranium, the construction of the plant itself (including the manufacture of all the component parts), and the decommissioning of the plant at the end of its useful life.)
With respect to coal versus natural gas, a study in the May 2011 issue of Climate Change Letters authored by three professors at Cornell University found that natural gas procured through hydraulic fracturing, or fracking, could be dirtier than coal, given the methane that leaks into the air during the fracking process. Moreover, given the greater global warming potential of methane as compared to carbon dioxide (roughly 23 times the global warming potential, by most estimates), even small leaks make a big difference. The Cornell study, led by Professor Robert Howarth, received considerable attention when its preliminary results were announced in late 2010, as the concept of natural gas as a relatively “clean” source of fuel was seriously disputed.
Now a competing study has been released by researchers at Carnegie Mellon University in Pittsburgh which concludes that natural gas produced in the Marcellus Shale gas basin is not as big a contributor fo climate change as coal. As reported in ClimateWire, researchers in Carnegie Mellon’s environmental engineering and business departments disagreed with Cornell in their study published earlier this month in the journal Environmental Research Letters. The Carnegie Mellon study concludes that procuring natural gas through fracking does not add significantly to the GHG emissions associated with “conventional” natural gas. The study found that Marcellus shale gas adds only 3 percent more emissions to the average conventional gas, thus preserving the claim of natural gas as being substantially cleaner than coal. Former Pennsylvania DEP Commissioner John Hanger states in his Facts of the Day blog that “[t]his careful study debunks and decimates professor Howarth’s hit piece study that the NYT gas reporter and other media gave so much attention.”
So the battle has been joined. It should be noted that both studies suffer from a lack of precise information about the start-to-finish footprint for natural gas production. The U.S. Environmental Protection Agency is proposing a new regulation that would require natural gas companies to collect these data, which should enable a more rigorous analysis to be conducted in the future. With the increased attention on life cycle analyses of GHG emissions, it can be expected that similar analyses will be required to be performed with respect to virtually all fuels used to generate electricity. Electric utilities typically attempt to place a cost on the environmental impacts of competing generating resources as part of the integrated resource planning process, such as by putting a “price” on carbon for purposes of comparing the GHG emissions produced by generating electricity from coal versus natural gas. It is a logical next step in that analysis to examine the GHG emissions over the fuel’s entire life cycle, rather than just the GHG emissions produced from combusting the fuel to generate electricity. So the debate will likely continue for years to come, and the veracity of the data will soon catch up to the rhetoric.