Will Switch From Diesel Trucks to Natural Gas Reduce Greenhouse Impact?

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 today 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 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.

Jonathan Camuzeaux

“The opportunity is there to achieve a climate benefit, provided we address the powerful emissions both from the fuel supply system and the vehicle”Jonathan Camuzeaux, Senior Economic Analyst, EDF

“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.

Pathway to Positive Climate Benefits
The study examines several types of engine technologies, and both liquefied and compressed natural gas fuels. Examining a range of options, the researchers found there are indeed pathways for heavy duty natural gas vehicles to achieve climate benefits, provided methane emissions across the value chain are reduced both upstream and at the vehicle level. Otherwise, it concludes that a conversion from diesel could lead to greater warming for the next 50 to 90 years before providing climate benefit.

Environmental Science & Technology Study

Reference case assumptions for all three natural gas fuel switching scenarios. Assumptions are expressed as absolute values (yellow and red points, right axis) and as the ratio of natural gas over diesel HDT values (bars, left axis).

Improvements in fuel efficiency could help ensure these vehicles are climate friendly. Today’s natural gas truck engines are typically five to fifteen percent less efficient than diesel engines. Consuming more fuel for each mile traveled reduces the relative CO2 savings. If that efficiency gap can be closed, natural gas trucks will fare that much better compared to diesel.

“The opportunity is there to achieve a climate benefit, provided we address the powerful emissions both from the fuel supply system and the vehicle,” Camuzeaux said.

A recent study by the technology consulting firm ICF International found that the oil and gas industry could cut methane emissions 40 percent or more for about one penny per thousand cubic feet of natural gas produced – about one-third of one percent at today’s prices – by replacing emissions-prone valves and properly maintaining pumps and other devices.

Upcoming Policy Opportunities
More information is needed to estimate with confidence the current climate footprint of trucks, and to get a better understanding of methane loss along the natural gas value chain. Significant research is underway to update estimates of methane emissions across the U.S. natural gas system, including the ambitious scientific research effort to publish 16 field studies launched by EDF and its partners.

The paper released today is separate from this ongoing effort and does not use any data from those studies, but it serves complementary purposes by emphasizing the need for more and better data on methane loss and providing a range of sensitivity analyses designed to understand various changing assumptions about emissions and efficiency.

“Policymakers who want to address climate change should use caution before promoting a switch to natural gas in the trucking sector until we are more certain about the magnitude of methane loss and have acted sufficiently to reduce emissions and improve natural gas engine efficiency,” Mathers said.

Image: Go By Truck