New Cornell Study Says Coal is Not Cleaner than Natural Gas
In March 2011, Cornell professors Robert Howarth, Renee Santoro and Tony Ingraffea published a peer-reviewed study in the journal Climatic Change titled, “Methane and the greenhouse-gas footprint of natural gas from shale formations” (see this MDN story). The study makes the claim that shale gas extraction is actually worse for the environment than burning coal because of greenhouse gases. Howarth et al’s conclusions were roundly refuted by both the U.S. Dept. of Energy (see this MDN story) and by a Carnegie Mellon University study (see this MDN story).
You can now add another group of Cornell professors to the list of those refuting the poor quality of the Howarth study. Cornell professors Lawrence M. Cathles, Larry Brown, and Andrew Hunter, along with Milton Taam (Electric Software, Inc.) have just published an article in the very same journal responding to the Howarth article. This new peer-reviewed article appears in the January 2012 issue of Climatic Change (a copy of the full article is embedded below).
Drs. Cathles, et al say that Howarth’s study is “seriously flawed,” that Howarth’s calculations for fugitive emissions—methane escaping into the atmosphere from shale gas drilling—are significantly overestimated, and that the timeframe they use—20 years instead of 100 years—leads to the wrong conclusion. According to Cathles and his co-authors, the greenhouse gas (GHG) footprint of natural gas is half, perhaps even one-third that of coal, not the opposite as Howarth argues.
From the article abstract:
Natural gas is widely considered to be an environmentally cleaner fuel than coal because it does not produce detrimental by-products such as sulfur, mercury, ash and particulates and because it provides twice the energy per unit of weight with half the carbon footprint during combustion. These points are not in dispute. However, in their recent publication in Climatic Change Letters, Howarth et al. (2011) report that their life-cycle evaluation of shale gas drilling suggests that shale gas has a larger GHG footprint than coal and that this larger footprint “undercuts the logic of its use as a bridging fuel over the coming decades”. We argue here that their analysis is seriously flawed in that they significantly overestimate the fugitive emissions associated with unconventional gas extraction, undervalue the contribution of “green technologies” to reducing those emissions to a level approaching that of conventional gas, base their comparison between gas and coal on heat rather than electricity generation (almost the sole use of coal), and assume a time interval over which to compute the relative climate impact of gas compared to coal that does not capture the contrast between the long residence time of CO2 and the short residence time of methane in the atmosphere. High leakage rates, a short methane GWP, and comparison in terms of heat content are the inappropriate bases upon which Howarth et al. ground their claim that gas could be twice as bad as coal in its greenhouse impact. Using more reasonable leakage rates and bases of comparison, shale gas has a GHG footprint that is half and perhaps a third that of coal.*
*Climatic Change (Vol 110, Jan 2012) – A commentary on “The greenhouse-gas footprint of natural gas in shale formations” by R.W. Howarth, R. Santoro, and Anthony Ingraffea