Exporting U.S. Natural Gas is as Clean as You Think

on June 13, 2014 at 10:00 AM

A liquified natural gas (LNG) tanker sit

Having read the U.S. National Energy Technology Laboratory (NETL) report, “Life Cycle Greenhouse Gas Perspective on Exporting Liquefied Natural Gas from the United States,” published on May 29, 2014, we are puzzled by the skewed conclusions reached by the Washington Post:

That U.S. exports of LNG to China could end up being worse from a greenhouse gas perspective than if China simply built a new power plant and burned its own coal supplies.”; and that “the benefits of cleaner, more efficient combustion of natural gas are largely offset by methane leakage in U.S. production and pipelines and by methane leaks and energy used in the process of liquefying and transporting the LNG.”

A correct reading of the report reaches a completely different conclusion.  After accounting for all the methane leakage factors mentioned by the Post, the NETL study clearly demonstrates that life cycle GHG emissions from LNG exports from the U.S. are significantly less than emissions from coal generated electricity in China and in Europe.  Figures 6-1 and 6-2 in the NETL report show that even using the 20-yr time horizon and the higher AR5 global warming potential (GWP) factor, average life cycle greenhouse gas (GHG) emissions from U.S. LNG exports to Europe are estimated at 787 (kgCO2e/MWh) versus 1,095 (kgCO2e/MWh) for coal, while U.S. LNG exports to China are estimated to generate 824 (kgCO2e/MWh) versus 1,095 (kgCO2e/MWh) for coal.  If we use the conventional IPCC 100-yr time horizon, which is mandated under the United Nations Frame Convention on Climate Change for official national GHG emission inventories, U.S.LNG exports look even better in terms of life cycle GHG emissions. For example, NETL estimates that on average U.S. LNG exports to China would have a GHG intensity of  660 (kgCO2e/MWh) versus 1,089 (kgCO2e/MWh) for coal.  In addition, the NETL report states that their results do not account for the anticipated 30 percent reduction in upstream life cycle GHG emissions for new unconventional gas wells in compliance with EPA’s 2012 New Source Performance Standards for the Oil and Gas sector.



The Washington Post also quotes critics of LNG exports that state that if more realistic “foreign and domestic (methane) leakage assumptions were used, the immediate climate impacts of LNG would be much worse.”  This statement is made despite the fact that Bill Gibbons, the DOE spokesman states that the NETL study uses a conservative estimate of 1.6 percent when the median EPA estimate is 1.4 percent. The Post then proceeds to quote leakage estimates made by Robert Howarth whose estimates have been soundly discredited by the professional literature and other studies that base their leakage rates on ambient air emissions measurement studies that have not been validated yet.  In fact, based on updated EPA estimation methods  for the national GHG inventory, methane emissions from natural gas systems represent 1.5 percent and 1.07 percent, respectively, of natural gas withdrawals (production) for 2011 and 2012.  More importantly, the general conclusion reached by this NETL study that electricity sourced from unconventional natural gas supplies would on average have lower GHG emissions from a life cycle perspective than electricity sourced from coal is supported by a significant number of the studies in the literature.

The NETL study does point out many of the limitations in performing an analysis of this magnitude and scope.  There are many uncertainties associated with assumptions made and the parameters chosen for the analysis.  For this reason, the NETL study describes some potential uncertainty ranges in the results based on the ranges for specific parameters.   These ranges are depicted as the black whisker plots on Figures 6-1 and 6-2.  Although most of the comparisons between coal and U.S. LNG show clear significant differences, there is one case (20-year time horizon analysis) where there is a slight overlap in the uncertainty ranges between U.S. LNG exports to China and coal.  It is disingenuous of the Post to focus on this worst case outcome as the primary result of the NETL study and as a basis for stating that LNG exports to China are worse than domestic coal consumption for electricity generation.

By Kyle Isakower 

Originally Posted June 11, 2014

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