Shifting from diesel fuel to natural gas to power the nation’s heavy duty commercial trucking sector would achieve widely promised climate benefits only if widespread emissions of heat-trapping methane across the natural gas value chain are reduced, according to a new study coauthored by researchers from Environmental Defense Fund (EDF) and published in the journal Environmental Science & Technology.
The findings have implications for truck and engine manufacturers, shippers, fleet operators and policy makers, many of whom look to the operational advantage in carbon dioxide emissions to justify the higher cost and reduced fuel efficiency of a natural gas truck, the researchers say. The challenge is that methane—the main ingredient in natural gas—has 84 times the warming power of CO2 over a 20-year timeframe. Methane is released to the atmosphere at every step from production wells to the vehicle fuel tanks.
“Natural gas trucks have the potential to reduce overall climate impacts compared to diesel, but only if we clean up the highly potent greenhouse gas emissions from the systems that produce and deliver the fuel,” said Jonathan Camuzeaux, a study author and Senior Economic Analyst at EDF. “Otherwise the net warming effect is actually a negative one for 50 to 90 years after the fuel is burned.”
Approximately 6.3 million metric tons of methane escaped from the natural gas value chain in 2013, according to the Environmental Protection Agency’s latest Greenhouse Gas Inventory Report, producing the same 20-year climate impact as about 111 million cars or 140 coal-fired plants. This wasted gas is worth more than $1.42 billion, and is enough to meet the annual needs of about 5 million homes.
“Technology moves fast. The time to get ahead of this question is now, before this industry hits a major growth spurt,” said Jason Mathers, a commercial transportation expert working closely with shippers and truck makers in EDF’s Corporate Partnerships Program. “Reducing methane leaks upstream of the vehicles themselves will determine whether a shift in fuels will have a cost or a benefit for the climate.”
Several policies are in play that could improve the climate prospects of natural gas trucks, including upcoming federal fuel efficiency and greenhouse gas standards for heavy trucks and recently announced federal upstream methane regulations. Natural gas vehicles currently use just 0.1 percent of the natural gas consumed in the U.S., but that number could rise significantly as demand for heavy duty natural gas vehicles grows, the report notes.
However, NGVAmerica, the national organization driving the use of natural gas as a transportation fuel, questioned the study.
“This study clearly demonstrates that there is a role for natural gas in addressing climate change. We welcome all credible insight into paths for improving emissions, yet it’s confusing that the Environmental Defense Fund has chosen to conduct and release another study, outside of the cooperative work already underway,” said NGVAmerica President Matthew Godlewski. “Many NGVAmerica members have worked in close collaboration with the EDF and its academic partners on a soon-to-be published ‘Pump to Wheels Methane Leakage’ study. This report is based on extensive research and provides a critical baseline to end speculation about actual in-use methane leaks from natural gas stations and vehicles.”
A diesel industry trade association, on the other hand, credited the researchers with using the new, clean diesel engines and comparing “’apples to apples’ to more accurately evaluate the two technologies.”
“This new report puts into perspective the complexity involved in evaluating alternative fuels in the transportation sector, and the importance in understanding the full picture before rushing to judgment about the merits of one technology over another,” said Allen Schaeffer, the executive director of the Diesel Technology Forum. ““With over 98 percent of all Class 8 trucks being diesel-powered, it is natural that alternative fuels such as natural gas are seeking and finding some niche markets in certain transportation sectors like waste management and urban-based delivery vehicles. As the authors suggest, this report does raise serious questions about whether large-scale moves to natural gas as a transportation fuel is truly a climate-positive consideration, or a move that could make things worse.”