“Renewable natural gas” (RNG) sounds good, but does it live up to the hype as a green alternative to fracked gas or is it something like the mythical “clean coal”— an invention of a high-powered advertising agency hired by a coal-industry front group? Like many things, the reality is a little more complicated than labels like “clean” or “green.”

Fracked gas is a fossil fuel. It’s made up primarily of methane (CH4) that was formed hundreds of millions of years ago from the decay of plant and animal waste and has been trapped deep underground ever since. Rather than leaving it undisturbed, we drill and frack to bring it to the surface where it either leakes into the atmosphere or is burned releasing carbon dioxide (CO2).  In either case, it’s pollution directly contributes to the climate crisis.

There is another fuel called “biogas” which isn’t a fossil fuel—it is formed from decaying waste in landfills, sewage plants, or livestock farms. Instead of releasing long buried pollutants, biogas is part of a carbon cycle where plants and animals take up carbon and then release it as waste a relatively short time later. This at least raises the possibility of having fuel use result in no net increase in carbon pollution.

While replacing fracked gas with biogas seems like an obvious solution, it doesn’t always work. Biogas has a much lower methane content and can contain much more CO2 along with many other chemicals. It isn’t the drop-in replacement we would like. That is where RNG comes in—it is biogas that has been refined to be a better substitute for fracked gas.

So, is substituting RNG for fracked gas the solution we are looking for? There is a temptation to compare RNG to fracked gas in isolation and conclude burning a biofuel is better than burning a fossil fuel. Unfortunately, that is answering the wrong question.

A lower-emitting version of fracked gas may be a useful tool in our toolbox, but that isn’t the ultimate goal. Our actual focus needs to be on the transition to a sustainable energy economy that gets us to net-zero carbon as rapidly as possible. This requires looking at the big picture and asking how RNG fits in our broader energy and environmental systems. It also requires looking at the specific sources of RNG and deciding if using it makes sense.

For example, one possible source for RNG is from manure produced at a concentrated animal feeding operations (CAFOs). These are industrial operations that raise far more livestock than a farm could naturally manage and, in the process, release huge amounts of pollution to our air and water. Having RNG as a marketable product makes CAFOs more profitable—effectively subsidizing more pollution.

Some may argue that capturing the methane from CAFOs and creating RNG is a better solution than releasing it into the atmosphere, but that is a false choice. Before we get to that point, we should recognize that CAFOs themselves are the result of policy choices that incentivise industrial agriculture operations at the expense of more sustainable farms. In a well designed system using more traditional farming practices, waste products can be fertilizer rather than being diverted for fuel.

There are similar issues on the demand side as well. Taking a narrow view one could argue that RNG is a better option for heating, cooking, and other fossil fuel uses. Looking at the big picture we can ask if the fuel use is necessary in the first place. Investments in energy efficiency can be a highly cost-effective way to reduce demand and electrification makes it possible to replace fuel use with clean and renewable energy like wind and solar.

RNG may have a role in a clean energy future, but at best it will be a supporting actor. We don’t have the capacity to make anywhere near enough RNG to displace the current demand for fracked gas, and what we can produce is significantly more expensive. That means that we have to think carefully about where it makes sense to use it.  

Also, RNG production is, at its core, a refinery operation. Even if it can be done in a way that is carbon neutral, there are still potential impacts on the environment and especially on neighboring communities. It might have a role in decarbonizing industrial applications that need methane as a feedstock, rely on combustion as part of the process, or for some other reason can’t effectively be electrified, but it’s not a panacea.  

For all its potential uses, there are some serious risks. The pipe-dream of RNG “solving the climate crisis” could easily become a convenient excuse or justification to build and maintain fossil fuel infrastructure. Doing so will lock in reliance on the fracked gas industry and other unsustainable business practices for years to come.  

Going forward we need to look at the big picture and prioritize our investments in the technologies and systems that we truly need.