Cow burps are a huge source of methane emissions.
Cow burps are a huge source of methane emissions.
James Temple

Climate Change / Carbon Sequestration

Turning one greenhouse gas into another could combat climate change

Sucking methane from the air might deliver a bigger bang for the buck than just removing carbon dioxide.

May 20, 2019
Cow burps are a huge source of methane emissions.

While carbon dioxide is the notorious villain of climate change, methane is actually a much more potent greenhouse gas.

The world doesn’t pump out nearly as much of it and its warming effect doesn’t last nearly as long, but molecule-for-molecule it traps 84 times more heat during the first two decades.

That fact provides the foundation for an unusual idea proposed in a paper released in Nature Sustainability today: By developing systems to capture a few billion tons of methane from the atmosphere, we could reduce short-term warming much more than we would by removing far more carbon dioxide.

“Methane removal would buy us considerable time to address the [larger] problem of carbon dioxide emissions,” says Rob Jackson, a professor of earth system science at Stanford and lead author of the paper.

It’s not the first time the idea has been floated. But Jackson and his coauthors took a closer look at what the climate benefits would be and how it could be done. Specifically, they proposed using zeolites, a class of minerals with very tiny pores, which are commonly used as industrial catalysts.

Most scientific models now show that the world will need to remove vast amounts of carbon dioxide to prevent sailing past dangerous warming thresholds, given how much has already been emitted and how little has been done to shift away from fossil fuels. A handful of startups are actively building prototypes and plants that can do this, including Climeworks, Global Thermostat, and Carbon Engineering (see “Startups looking to suck CO2 from the air are suddenly luring big bucks”).

But while it would likely be necessary to remove hundreds of billions of metric tons of carbon dioxide to return to preindustrial levels, you’d only need to eliminate 3.2 billion tons of methane to get back to earlier levels of that gas.

Doing so would reverse one-sixth of the total warming effect of all greenhouses gases in the atmosphere, the study found.

Crucially, this all assumes that the methane would be converted into carbon dioxide and released again, by heating the trapped molecules. In other words, merely turning one greenhouse gas into another one would still provide very significant reductions in warming. The captured methane could be stored and converted into other products as well, but that would add a lot of cost and complexity to the process.

To be sure, removing methane is a trickier task than capturing carbon dioxide, mainly because it’s far more dilute in the atmosphere. While removing CO2 means plucking one molecule from among some 2,400 others in the air, capturing methane means snatching one nested amid more than 500,000.

But the authors suggest it could be done, in one scenario, by using giant electric fans to suck air into tumbling chambers, where powdered zeolites would cling to methane molecules.

While it’s likely to cost more than carbon capture on a per-ton basis, “it could yield greater climate and economic value because of methane’s greater potency as a greenhouse gas,” the authors note. Scaling up industrial operations of this sort would almost certainly require government mandates or a much higher price on carbon emissions and offsets than exist in most markets today.

While there are some significant uncertainties here, the authors say the potential payoff warrants a substantial research effort to explore the possibilities further.

As with carbon dioxide, it would be far easier and cheaper to prevent emissions of the methane in the first place than to remove it after the fact.

“It’s like a drop of ink,” Jackson says. “If you can catch it before it goes into the water, it’s a lot easier to remove than once it’s spread throughout.”

Agriculture and livestock are the largest sources of anthropogenic methane emissions, accounting for around 200 million tons annually. There have been efforts to cut these emissions from areas like rice cultivation, burping livestock, and animal manure by changing when fields are drained, adjusting what animals eat, and incorporating the use of biodigesters, respectively (see “Seaweed could make cows burp less methane and cut their carbon hoofprint”). But none of these have proved to be complete solutions to date.

Meanwhile, oil and gas companies release some 100 million tons of methane per year through pipeline leaks and flaring at oil and gas sites, and have resisted efforts to tighten regulations.  

Jackson says that while methane removal makes the most sense as an early tool, it could also play a role in the long term as well, by cleaning up the methane emissions we ultimately can’t, or opt not to, eliminate.