New Research Suggests Renewable Natural Gas Can’t Deliver The Carbon Neutral Future We Need

In the fight to supplant fossil fuels and build a climate friendly global economy, Renewable Natural Gas (RNG) has been proposed as a prudent and cost-effective method of decarbonizing fossil-based natural gas. As a carbon negative fuel source that works interchangeably in the hydrocarbon infrastructure we already have, RNG promises a rapid offsetting of the anthropogenic carbon dioxide (CO₂) emissions from fossil gas without the need to reconfigure large portions of our energy delivery system. Mix some carbon-negative RNG in with fossil natural gas and voilà: the overall mix is carbon neutral. New research out of Georgia Tech, however, paints a different picture: at any meaningful scale RNG is likely to be carbon-intensive.

The promise of RNG is rooted in the comparatively high global warming impact of methane, the primary ingredient in natural gas. Although CO₂ gets all the attention, methane is a significantly more potent greenhouse gas, having a global warming potential approximately 30 times greater than CO₂. Methane is generated as a natural byproduct of many modern processes, from landfills to waste-water treatment to diary farming. In these systems, organic materials are broken down by bacteria, generating methane, which generally has escaped to the atmosphere, contributing to global warming. If that waste methane is instead captured and utilized in an engine, water heater, cooking stove, or other device normally fueled by natural gas, the global warming impact of the methane emissions is avoided. As a result, RNG under this scenario is carbon negative.

As the new research shows, however, this math only works if the captured methane is truly a waste methane that was otherwise going to be released to the atmosphere. Since the amount of waste methane that fits this bill is a small fraction of the need, any structure that rewards the production of RNG is likely to create an incentive for producers to make more “waste” methane for capture. As a result, any action to scale RNG production will make it increasingly difficult to determine what portion of produced RNG is resultant from methane that was truly a waste product that would not have been otherwise captured and utilized. Methane purposefully created to be captured and used as RNG isn’t really a waste: if it weren’t for the desire to make RNG, it never would have been created and therefore was never at risk for release to the atmosphere. That means a lot of RNG would simply be, at best, carbon neutral.

Carbon neutral still sounds pretty good compared against fossil natural gas, but as the authors point out, the very gas infrastructure RNG hopes to utilize undermines even that promise. The problem is that our gas infrastructure is leaky, and if most of the RNG produced is mere carbon-neutral, the release of even a small fraction through these leaks quickly undermines its climate-friendly bonafides. The result is RNG turned upside down: a system designed to prevent the release of waste methane instead becomes a system that leaks manufactured methane. The utilization of RNG at scale to supplant meaningful quantities of natural gas would still be less carbon-intensive than fossil natural gas, but it is not a system that is carbon neutral, let alone carbon negative. As the authors argue, if decarbonization is the sole consideration, waste methane is best utilized in an on-site flare (or other on-site usage); the fossil gas grid is better replaced with electrification, green hydrogen, or other solutions.

This doesn’t necessarily mean that RNG is of no value in the fight to decarbonize: RNG is demonstrably better than fossil gas, and it has the ability for rapid deployment through existing infrastructure. But its no panacea: RNG production and use at scale is still carbon-intensive, and incentivizing its use now will lock in its production for decades. Policymakers aiming for a carbon-neutral future should take note: RNG, if part of the solution, is at best an incremental step to bridge the gap while a more permanent change away from gas usage takes hold.