A handful of startups are using machines to suck CO2 from the air in an attempt to slow down climate change. But some researchers think there could be even more of an impact from removing methane, a greenhouse gas that traps much more heat than carbon dioxide does.
In the first couple of decades after it’s released, a molecule of methane has more than 80 times the warming power of a molecule of CO2. That means that removing methane can also have a major impact. If new methods for methane removal can be proven and scaled up, “it would be extremely powerful,” says Lena Höglund-Isaksson, a senior research scholar at the International Institute for Applied Systems Analysis. If the concentration of methane in the atmosphere could be cut in half, restoring pre-industrial levels, it could help cool the planet by around half a degree Celsius—a huge amount that might make it possible to keep global warming below 1.5 degrees by the middle of the century, if CO2 emissions also drop.
“There are not many technologies that could actually address the problem that we are facing in the next couple of decades, where we know that it will be very, very hard to stay below 1.5 degrees [Celsius], given that so much CO2 has already been emitted and that will continue to be emitted for some time,” she says.
Methane emissions have grown quickly, especially in the oil and gas sector, where the gas is emitted during production and from leaks in pipelines. Emissions also come from agriculture (via cow belches and manure) and landfills. Several countries recently pledged to reduce methane emissions by 30% by 2030; scientists say that it’s feasible to go farther and cut emissions in half this decade. Reducing emissions can only partly help, since so much methane is already in the atmosphere. Taking the extra step to remove methane from the air could potentially start to reverse warming.
There are several potential ways to deal with methane, from photocatalytic paints, which can break the gas down, to polymers embedded with microbes that naturally eat methane. But one of the most promising might be a method that adds extra iron to the air, speeding up the process by which methane naturally breaks down. (Unlike carbon dioxide, which stays in the air for centuries, methane breaks down in roughly a decade.)
“The advantage of our solution, compared to other methane removal technologies, is that our solution is the only one that we know of that may be able to remove atmospheric methane cost-effectively,” says Maarten van Herpen, a scientific advisor to Methane Action,a nonprofit working to assess, test, and eventually deploy viable methane removal technologies, including the new iron process, which it is working on with scientists at the University of Copenhagen. Iron chloride, which occurs naturally in the air, releases chlorine atoms when exposed to the sun, and those atoms break down methane.
The exhaust from container ships already release iron emissions over the ocean, where the iron reacts with sea salt in the air to form iron chloride. The researchers want to test the impact of adding extra iron particles to the fuel that ships burn, or spraying iron particles into the ship’s exhaust. “Deploying [iron-salt aerosols] through global shipping has the added value that we can make use of existing infrastructure, enabling potential rapid global diffusion and scale up of the technology at relatively low cost,” van Herpen says. That’s also an advantage compared to CO2 removal, which is very expensive now and requires a lot of energy, making it difficult to scale up.
The method still has to be tested outside the lab, but the researchers are in talks with ship owners to potentially begin the process. They need proof that it works in the real world—and that it doesn’t unintentionally cause different problems. It’s also something that has to happen in addition to all the work to decarbonize the economy; without also eliminating CO2 emissions, the 1.5-degree Celsius goal is out of reach. But it could be a very useful tool.
“Many policymakers are not aware that this possibility exists,” says Höglund-Isaksson. “I think many have ruled out the possibility of atmospheric-methane removal, and I think we need to bring awareness back that maybe there is actually a possibility of it. And it’s really worth seriously looking into if this is something that can prove useful.”