Correspondence/Rebuttal pubs.acs.org/est
Comment on “Environmental Implications of United States Coal Exports: A Comparative Life Cycle Assessment of Future Power System Scenarios”
R
used for electricity.4 The same is not true when looking at international markets. Potential importers of U.S. coal, including South Korea, use significant levels of coal for industrial and other uses. Normalizing to tons instead of MWh allows cross-sectoral emissions quantification and is more comprehensive. The study justifies the use of MWh by arguing that normalizing to tons does not account for the higher efficiency of Korean plants. While this is true, normalizing to tons addresses the key question that bears on the export debate: what are the lifecycle greenhouse gases associated with using a ton of coal internationally versus how it would (or would not) be used in the United States? A ton of coal produces the same amount of carbon dioxide no matter where or how efficiently it is burned. Even if using a MWh normalization was the best method, which it is not, the study unreasonably combines emissions from American and Korean electricity generation together. That is, the authors average emissions per MWh in the United States with emissions per MWh in Korea. This allows the large emissions intensity decrease from replacement of coal with gas in the United States to hide the increase in emissions intensity from using PRB coal to replace any other source of electricity in South Korea. Not only is this an unprecedented accounting method, it misleads readers, misses emissions from nonelectric uses of coal, and obscures the central question of how US coal exports impact absolute emissions globally. Finally, the study excludes emissions impacts from the potential use of fossil sources in South Korea that would be displaced by American coal. While the study acknowledges this, it justifies it by arguing that “boundaries” need to be made somewhere. This creates a methodological inconsistency that includes assumed domestic market impacts but excludes impacts on international market. One recent study found that the building of the Keystone pipeline could lead to greater global oil consumption by lowering prices and increasing demand.5 A similar effect is likely in the coal market. By increasing availability of coal on the world market, prices would fall and overall consumption would tend to increase. This would lead to greater emissions globally. By failing to address international markets, the study offers an incomplete lifecycle picture of coal exports. In sum, key methodological shortcomings undermine Bohnengel, Patiño-Echeverri, and Bergerson’s conclusions regarding climate impacts. The study’s conclusion that, in a certain scenario with specific boundaries and assumptions, greenhouse gas emissions per global MWh would decrease is literally true. However, that scenario depends on a counterfactual baseline, a misleading normalization method, and unjustified assumptions about the behavior of domestic and international coal markets. When correcting for these factors, it
ecently, Bohnengel, Patiño-Echeverri, and Bergerson attempted to quantify the potential greenhouse gas emissions associated with exporting coal from the United States.1 However, the study’s conclusions are undermined by several methodological issues and limitations: the study identifies an inaccurate baseline scenario, uses an improper normalization method, and does not consider the broader market impacts of coal exports. The study’s baseline scenario is not based on an appropriate baseline. In the study’s baseline scenario two coal plants in the Northwest are retrofitted with pollution control equipment and continue to be operated. In the export scenario, these plants are instead closed down and replaced with natural gas, with the coal exported overseas. However, the two plants in question, Centralia in Washington and Boardman in Oregon, are already scheduled to be shut down within the next decade and will most likely be replaced with natural gas.2,3 The authors do not explicitly acknowledge that these plants are already scheduled to be shut down and have an extremely low likelihood of being retrofitted. Rather, they identify their baseline scenario as “hypothetical,” which is misleading as it implies a business as usual case to readers. Therefore, the study’s baseline scenario is actually a counterfactual scenario. The domestic emissions of their export scenario are representative of the true baseline. This is critical, as the reduction in carbon emissions intensity the study finds is solely due to inclusion of replacing coal generation at Boardman and Centralia with natural gas generation, and would not occur if the study’s baseline scenario was representative of reality. This point is underscored by the study itself, which indicates that burning Powder River Basin (PRB) coal is more greenhouse gas intense than all other potential sources of Korean electricity generation, including current coal use. Only by expanding the study’s boundary to include changes that will happen regardless of whether coal is exported can the authors conclude that there are potential greenhouse gas intensity benefits. The study omits a third scenario where coal is not exported or used domestically. The authors explicitly acknowledge their assumption the coal would be burnt anyways but do not provide a sufficient justification. One of the major potential uses of the study is determining whether coal exports are good from a greenhouse gas perspective. By failing to consider the threshold question of whether exports enable continued consumption of coal that would otherwise be left in the ground, the study fails to comprehensively assess potential domestic impacts of exports. The study uses a misleading and inappropriate normalization method that is not well suited to assessing emissions from exports. The major metric used by the authors, emissions per megawatt hour (MWh), is useful for comparison against other electricity sources in the U.S., where coal is almost exclusively © 2014 American Chemical Society
Published: November 18, 2014 14053
dx.doi.org/10.1021/es504394q | Environ. Sci. Technol. 2014, 48, 14053−14054
Environmental Science & Technology
Correspondence/Rebuttal
is apparent that exporting PRB coal to South Korea will lead to an increase in global greenhouse gas emissions on both an absolute and intensity basis.
Alexander Q. Gilbert*
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Energy Analyst, Haynes and Boone, LLP, 1212 Irving St. NW, Washington, DC 20010, United States
AUTHOR INFORMATION
Corresponding Author
*Phone: 303-625-3705; e-mail:
[email protected]. Notes
The authors declare no competing financial interest.
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REFERENCES
(1) Bohnengel, B.; Patiño-Echeverri, D.; Bergerson, J. Environmental implications of United States coal exports: A comparative life cycle assessment of future power system scenarios. Environ. Sci. Technol. 2014, 48 (16), 9908−9916 DOI: 10.1021/es5015828. (2) Craig Welch, “Prior agreement to phase out Centralia coal plant will cover most emissions reductions.” Seattle Times. June 2, 2014. http://seattletimes.com/html/localnews/2023753691_ carbonwalocalxml.html. (3) Scott Learn. “PGE’s coal-fired Boardman plant gets approval to close in 2020, with fewer pollution controls.” The Oregonian. December 9, 2010. http://www.oregonlive.com/business/index.ssf/ 2010/12/pges_coal-fired_boardman_plant.html. (4) Cathles, L. M., III; Brown, L.; Taam, M.; Hunter, A. A commentary on “The greenhouse-gas footprint of natural gas in shale formations” by R.W. Howarth, R. Santoro, and Anthony Ingraffea. Clim. Change. 2012, 113 (2), 525−535. (5) Erickson, P.; Lazarus, M. Impact of the Keystone XL pipeline on global oil markets and greenhouse gas emissions. Nat. Clim. Change 2014, 4, 778−781.
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