Abstract

In order to minimize adverse impacts of global climate change, the need to reduce greenhouse gas (GHG) emissions from electricity generation is now widely recognized. In this context, natural gas has been proposed as a bridge fuel offering short-term reductions in GHG emissions prior to long-term deployment of renewable sources such as solar, wind, and hydroelectric. Natural gas has been proposed as a bridge fuel because, without leakage, its carbon dioxide-equivalent emission (i.e., its GHG footprint) is approximately half that of coal per kilowatt-hour of electricity generated. However, the primary component of natural gas is methane, whose global warming potential (GWP) is significantly larger than the reference gas carbon dioxide. This means leakage reduces natural gas’s GHG advantage over coal. Indeed, with enough leakage, natural gas has a larger GHG footprint than coal. This seminar answers the question: How much leakage renders the GHG emissions from natural gas equivalent to coal? This question is answered using a simple model that assumes the GHG footprint for each fuel is the sum of emissions from (1) electricity generation and (2) methane leakage. Emissions from electricity generation are taken from published life-cycle assessments. Assuming natural gas is 80% methane, emissions from leakage are converted to carbon dioxide-equivalent emissions using GWP factors provided by the Intergovernmental Panel on Climate Change. Results are presented on a single figure showing the GHG footprint of electricity from natural gas, coal, and renewables as a function of methane leakage and time horizon. This figure shows what leakage allows near-ideal GHG emissions, what leakage makes coal-equivalent GHG emissions, what leakage renders GHG emissions exceeding coal, and how these rates depend on the time horizon selected. The conclusion of this analysis is that control of leakage is essential for natural gas to offer reduced GHG emissions compared to coal.