What will it take to get sustained benefits from natural gas?

Examining the climate impacts of methane leakage from natural gas

There has been much confusion about the impacts of increased natural gas use on the climate. While natural gas burns cleaner than other fossil fuels when combusted, methane leakage from the production, transportation, and use of natural gas has the potential to undermine some or all of those benefits, depending on the leakage rate. Methane is the main ingredient in natural gas and a greenhouse gas (GHG) pollutant many times more potent than carbon dioxide (CO2), the principal contributor to man-made climate change.

In other words, leaks during the production, distribution, and use of natural gas could undermine the greenhouse gas advantage combusted natural gas has over coal and spell major trouble for the climate.

Methane leakage study

The good news is that leaks can be detected, measured – and reduced. EDF is currently collaborating with industry and academic partners on a series of five scientific studies to measure methane leakage rates across the natural gas supply chain. Among our partners are the University of Texas (UT), Duke University, Harvard University, Boston University and leading natural gas companies. EDF aims to complete the entire study by December 2013.

The first study, set for completion in January 2013, seeks to estimate the methane emission rates from participating companies’ natural gas production by conducting direct measurement techniques at a sample of natural gas production sites. It brings together EDF, UT and nine of the nation’s leading natural gas producers: Anadarko Petroleum Corporation, BG Group plc, Chevron Inc., Encana Oil & Gas (USA) Inc., Pioneer Natural Resources Company, Shell, Southwestern Energy, Talisman Energy, USA, and XTO Energy, an ExxonMobil subsidiary. Findings from the study could help guide how companies, states and the federal government measure, monitor and manage methane emissions.

Methane leakage paper

An enhanced method for assessing climate impacts from natural gas development and use is offered in Greater focus needed on methane leakage from natural gas infrastructure, a scientific paper in Proceedings of the National Academy of Sciences co-authored, with others, by EDF scientists Ramon Alvarez and Steve Hamburg.

The paper illustrates the importance of accounting for methane leakage across the value chain of natural gas (i.e. production, processing and delivery) when considering fuel-switching scenarios from gasoline, diesel fuel and coal to natural gas.

Key findings of the PNAS paper, based on the best available estimates on methane emissions from the EPA, include:

Assuming the Environmental Protection Agency’s (EPA) 2009 leakage rate of 2.4% (from well to city), new natural gas combined cycle power plants reduce climate impacts compared to new coal plants; this case is true as long as leakage remains under 3.2%.
Assuming EPA’s estimates for leak rates, compressed natural gas (CNG)-fueled vehicles are not a viable mitigation strategy for climate change because of methane leakage from natural gas production, delivery infrastructure and from the vehicles themselves. For light-duty CNG cars to become a viable short-term climate strategy, methane leakage would need to be kept below 1.6% of total natural gas produced (approximately half the current amount for well to wheels – note difference from well to city).
Methane emissions would need to be cut by more than two-thirds to immediately produce climate benefits in heavy duty natural gas-powered trucks.
At current leakage rate estimates, converting a fleet of heavy duty diesel vehicles to natural gas would result in nearly 300 years of climate damage before any benefits were achieved.

Related resources

Methane leakage model

Our economics team has created a methane leakage model based on the science in the PNAS paper. The model explores the climate implications of reducing emissions from natural gas systems in the context of a switch towards natural gas-fueled technologies.

To use the model, enter a policy case of desired values for natural gas leak rates and sector fuel mixes. Power plant efficiencies can also be modified. The model outputs a graph and summary table of the impact of that policy case on the climate. Results are represented as a percentage change in net radiative forcing relative to 2010 U.S. emissions.

Model, user guide and sample scenarios