September 21, 2017

Lifecycle Greenhouse Gas Emissions: From Shale Gas Compared to Coal

David H. Hughes

An Analysis of Two Conflicting Studies

Two studies with conflicting conclusions have recently been produced on full-cycle greenhouse gas (GHG) emissions from shale gas production, one from scientists at Cornell University and another from a scientist at the National Energy Technology Laboratory (NETL). The Cornell study, published in a peer-reviewed journal, suggests that lifecycle GHG emissions from shale gas are 20%-100% higher than coal on a 20-year timeframe basis, especially considering that 70% of natural gas consumption is not used for electricity generation. The NETL study, presented in a talk at Cornell University and later posted on the NETL website, suggests, on an electricity-generation comparison basis, that natural gas base load has 48% lower GHG emissions than coal on a 20-year timeframe basis. The NETL comparison, however, does not single out shale gas, which is projected by the U.S. Energy Information Administration (EIA) to be the major source of natural gas supply growth going forward, nor does it consider the overall emissions from natural gas-fired electricity generation, focusing instead on the more efficient base load combined cycle component.

When the assumptions of the NETL study are examined in detail and compared to the U.S. Environmental Protection Agency (EPA) 2009 emissions inventory for natural gas, as well as to the likely ultimate production from shale gas wells, the resulting conclusions are not significantly different than the Cornell study. Shale gas full-cycle GHG emissions are higher than those of coal when comparing both the existing electricity generating fleets and best-in-class electricity generation technologies for both fuels over a 20-year timeframe basis, but are lower than those of coal on a 100-year timeframe basis. This has significant policy implications for utilizing natural gas as a “transition” fuel to a low carbon future in mitigating near-term GHG emissions.

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