(724b) Streamlining Lifecycle Greenhouse Gas Emissions of Coal, Conventional and Unconventional Natural Gas for Electricity Generation

An analysis of the lifecycle greenhouse gas (GHG) emissions associated with natural gas use recently published by Howarth et al. (2011) stated that use of natural gas produced from shale formations via hydraulic fracturing would generate greater lifecycle GHG emissions than petroleum per unit of energy input.  The analysis also suggested that the lifecycle GHG emissions from natural gas (at the point of input into a power plant) could exceed (or be “quite similar to”) those from coal. We re-evaluated the estimated lifecycle GHG emissions from Howarth’s study, reviewed other published literature on lifecycle analysis of natural gas and coal, and calculated normalized full lifecycle emission factors per MWh of base load electricity generated.  The CO₂equivalents were presented on both 20- and 100-yr time horizons to evaluate both near- and long-term impacts. Howarth et al. (2011) raise valid points regarding the need for considering emissions over the full lifecycle, including fugitive CH₄ emissions from hydraulically-fractured natural gas wells and distribution systems, as well as the need to recognize the time basis (e.g., 20-yr, 100-yr, 500-yr) for comparing the climate impacts of different energy sources.  However, because their analysis did not account for the efficient use of natural gas in advanced combustion technologies, their estimates appear to be much more representative of worst-case conditions than average industry emissions.