The Trouble with Natural Gas as a Fuel Source for Trucks

We can and should make natural gas into a fuel that, on balance, is environmentally less harmful than diesel

Jason Mathers
Jason Mathers

At the Environmental Defense Fund, we’re constantly seeking ways to make a more environmentally responsible way of doing business work for the businesses themselves. If it doesn’t look good on the bottom line, it’s going to be a lot harder to implement changes. Period. Often, the real challenge comes when something looks great, both environmentally and economically, but if you shift the range of view, you see it’s not that simple after all. The adoption of a natural gas as a fuel alternative to petroleum-based products in heavy-duty freight trucks is a pithy example and it’s worth digging into.

For that purpose, we commissioned a study coauthored by researchers from EDF and published in May in the journal Environmental Science & Technology. Their report, “Influence of Methane Emissions and Vehicle Efficiency on the Climate Implications of Heavy-Duty Natural Gas Trucks,” gives a very clear picture of the pros and cons of natural gas as a freight fuel.

Combusting natural gas instead of diesel reduces carbon dioxide (CO2) emissions per unit of energy by about 30 percent. But natural gas trucks are less efficient than diesel trucks, which reduces the CO2 savings per mile to about 20 percent. Taking into account methane emissions across the natural gas supply chain, the report clearly shows that, if we carry on as we are, the net effect of switching to natural gas is actually to cause negative impact on the climate over the next 50 to 90 years compared to remaining with diesel.

The good news is that we can and should make natural gas into a fuel that, on balance, is environmentally less harmful than diesel. But it’s not yet a done deal, and the devil, as always, is in the details.

Methane Is a Powerful Greenhouse Gas

The problem, in many ways, is quite simple. Harvesting natural gas from the ground and delivering it through a supply chain to a fuel pump, the way it’s currently done, involves allowing a certain proportion of methane—the main component of natural gas—to escape into the atmosphere. Some of the methane is released deliberately, when there’s too much pressure at a well-head, for example. Some is released by accident as the gas gets transferred from one container to another on its way into the belly of a tractor. And methane is an incredibly powerful greenhouse gas. Molecule for molecule, methane has 84 times more warming power than CO2 over a 20-year timeframe.

The math of methane’s effect on global warming quickly erodes the advantages it presents as a clean-burning fuel. Right now, the vast network of infrastructure—including wells, pipelines and storage facilities—that produces, transports and distributes natural gas is the largest single source of methane emissions in the U.S. That translates into approximately 6.3 million metric tons of methane that 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.

Natural gas trucks most certainly present the opportunity to reduce overall climate impacts compared to diesel, but only if we clean up these highly potent greenhouse gas emissions from the systems that produce and deliver the fuel. Meanwhile, diesel engine efficiency is likely to improve in the future (particularly as a result of current and upcoming heat deflection temperature standards), and if this occurs without similar improvements in natural gas engine efficiency, a growing spread between these engines could worsen the impacts of diesel to natural gas fuel switching.

The Oil and Gas Sector Can Reduce Emissions by More than 40 Percent at Minimal Cost

Combining reductions in methane emissions with engine efficiency improvements could lead to substantial climate benefits.

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 1 percent at today’s prices—by replacing emissions-prone valves, and properly maintaining pumps and other devices.

Several policy mechanisms are in play to help, including:

  • The recently announced federal upstream methane regulations.
  • Upcoming EPA/NHTSA MD-HD Standards Phase II, which can minimize on-vehicle methane emissions from engines and liquefied natural gas (LNG) tanks.

In the meantime, policymakers wishing to address climate change should use caution. Natural gas is by no means a no-brainer, environmentally or otherwise.

Technology is a great ally and it develops quickly. The time to get ahead of this issue is now, before both the natural gas and the freight industries hit a major growth spurt. 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.

EDF is advocating for critical policy advancements because we want to see natural gas trucks deliver climate reductions. Stakeholders in the supply chain have a role to play in advancing these solutions, too. As shippers and logistics providers adopt natural gas trucks, they should also be supporting the policies necessary to ensure these vehicles deliver on their environmental potential.