Pulling molecules of planet-warming carbon dioxide straight from the air has been likened to finding needles in a haystack. Removing methane, a shorter lived but far more potent greenhouse gas produced by rice paddies and oil wells, is more like finding specks of dust on the head of a needle in the hay.
That’s why a report released today from the U.S. National Academies of Sciences, Engineering, and Medicine (NASEM) recommends spending between $150 million and $400 million over 3 to 5 years on the problem, much of it to answer whether it’s even feasible to capture a molecule that makes up just 2 parts per million (ppm) in the atmosphere.
“This has been a very underexplored and underresourced field,” says Erika Reinhardt, executive director of Spark Climate Solutions, a U.S.-based nonprofit trying to spur research into climate pollutants such as methane. “My hope for the report is that it helps to highlight some of those research needs,” says Reinhardt, who was not involved with the NASEM study. She estimates just $10 million worldwide has been spent on methane removal research.
Methane’s role in global warming is getting more attention. Scientists are using satellites to better track emissions, which are rising and projected to grow this century. Although methane concentrations are far lower than current carbon dioxide levels of roughly 420 ppm, the gas converts sunlight to heat more effectively, making it ton-for-ton 80 times more potent than carbon dioxide over a 20-year span. Methane is estimated to be responsible for one-third of global warming during the industrial era.
To date, scientists and policymakers have focused on keeping methane out of the atmosphere—stanching flows from hot spots such as oil and gas pipelines and landfills. But those represent as little as 21% of total methane emissions in recent years. The rest comes from more diffuse societal sources, such as coal mines and cow burps, as well as natural ones, such as swamps and thawing permafrost.
Rising emissions from such places and the hunt for more ways to rein in global temperatures could create more pressure to remove methane directly from the atmosphere, says Gabrielle Dreyfus, the NASEM committee chair and chief scientist at the Institute for Governance & Sustainable Development, a think tank promoting research into climate “superpollutants.” “There might be a gap between where we want to be in methane concentrations and methane emissions, and the tools we have to get there,” she says.
Any approach to methane removal will be more challenging than attempts to suck carbon dioxide from the air at industrial scales, says Christopher W. Jones, a committee member and chemical engineer at the Georgia Institute of Technology. Because methane is so dilute, more air would need to be processed to remove meaningful amounts of it. And the molecule is less “sticky”—making it harder to separate from the air by getting it to bind with other chemicals, Jones says.
There is an advantage, however. Methane, the primary ingredient in natural gas, is transformed relatively easily into carbon dioxide and water when it is burned or broken down in other oxidation reactions. The question is “how do you engineer a device, building, leaf, soil that makes that oxidation rate move faster,” Jones says. “That’s really the name of the game.”
The committee highlighted five potential approaches that deserve investigation. They include machines that would concentrate methane and ones that would break it down; methane oxidation catalysts that could be added to surfaces that come into contact with a lot of air, such as wind turbine blades; ways to tweak ecosystems to break down methane faster, for instance by increasing the abundance of methane-digesting microbes; and strategies to boost airborne chemicals, such as chlorine or hydroxyl ions, that would speed up the breakdown of methane and shorten its natural lifetime of roughly a decade. (Carbon dioxide, by contrast, persists for centuries.)
But today, there are no technologies capable of tackling methane at levels below 1000 ppm, which is 500 times atmospheric levels. The committee urged that much of the money it recommends go toward a better understanding of basic methane dynamics, such as how methane ebbs and flows through the atmosphere and ecosystems. It also called for more study of social aspects of the research, such as how to include the public in deliberations about what kind of technology is acceptable.
Because it’s just beginning, methane removal research might be able to avoid some of the problems that have bedeviled other climate interventions, says Sikina Jinnah, a committee member and University of California, Santa Cruz social scientist. “It’s not enough to just tack on a social scientist to a grant at the end when you’ve already decided what the project is going to be,” she says.
Although the field is in its infancy, scientists are making headway toward grabbing methane in places where it is concentrated. Desirée Plata, a geochemist and environmental engineer at the Massachusetts Institute of Technology, is preparing to go to a coal mine to test a clay-based material that can trap and speed the breakdown of methane. There, she will tap into a plume of methane-rich air pulled from the mine shafts by giant ventilation fans. If it works, the technology could help control emissions from mines that total more than 40 million tons per year, some 10% of total anthropogenic methane.
Although the technology could work to remove methane from regular air, it would be energy intensive and inefficient, Plata says. Better to focus on places like the coal mine, where the gas is found at levels 500 to 10,000 times greater. Today, “It just doesn’t make sense to treat those lower levels,” she says.
More: https://www.science.org/content/article/slow-global-warming-could-methane-be-stripped-air
