Removing carbon dioxide from the atmosphere is essential to meeting international climate goals, scientists say. Without it, it’s all but impossible to reach net-zero greenhouse gas emissions in time to limit global warming to 1.5 or 2 degrees Celsius, the primary targets of the Paris climate agreement.
Yet carbon dioxide isn’t the only climate-warming gas that needs a sharp cutback in the atmosphere. Experts are turning their focus to methane as well.
On Tuesday and Wednesday, the National Academies of Sciences, Engineering and Medicine hosted a workshop dedicated to atmospheric methane removal, which is the process of removing methane emissions directly from the air.
The workshop included presentations by dozens of researchers and policy experts addressing questions about the science and effectiveness of methane removal, potential side effects and unintended consequences and the ways it should be governed and regulated.
These presentations will be used to inform a forthcoming NASEM report on atmospheric methane removal. The study will examine the global need for methane removal, viable options for carrying it out and potential risks and benefits, while outlining a road map for future research.
The subject is more complicated than carbon dioxide removal, which has received more attention and research.
Methane has a far shorter lifetime in the atmosphere than carbon dioxide, yet it’s a much more potent greenhouse gas while it lasts. The world already has warmed by more than 1 degree Celsius since the Industrial Revolution, and scientists estimate that methane may be responsible for as much as 0.5 degrees.
Reducing methane emissions is at their sources is a growing priority. At the same time, scientists say, removing methane directly from the atmosphere is essential to meeting the world’s climate goals.
There are many ways to suck carbon dioxide back out of the atmosphere, from planting trees to building carbon-guzzling machines. Many of these solutions require large land, water or technical resources and have yet to be implemented at a globally meaningful scale.
Yet the concepts are relatively well researched and understood.
Methane removal, by comparison, is more complex and more difficult. For one thing, methane is far less abundant in the atmosphere than carbon dioxide, meaning methane capture systems must process much larger quantities of air in order to make a meaningful difference.
Scientists are working on various techniques. Researchers at this week’s workshop presented a variety of strategies, including methane-absorbing minerals, methane-eating microorganisms and special chemical reactions involving chlorine atoms, which can help scrub methane from the atmosphere.
Still, questions remain about how well these strategies would work and whether they could be scaled up quickly enough to make a meaningful dent in global methane concentrations.
There are also uncertainties about unintended side effects of some emerging technologies. Adding chlorine to the atmosphere, for instance, can actually increase the lifetime of methane in the atmosphere if it isn’t carefully dosed. It can also attack the Earth’s protective ozone layer.
On the other hand, chlorine-based methods could decrease certain other types of climate-warming gases in the atmosphere in addition to methane.
“There’s a lot of competing pluses and minuses when you talk about these methods,” said Hannah Horowitz, an environmental engineer at the University of Illinois, Urbana-Champaign, in a presentation at the workshop.
Presenters also discussed the need for more studies on the social impacts of methane removal techniques and more discussions on the ways they should be governed and regulated.
Because methane removal is still an emerging field, with many remaining scientific uncertainties, communities likely will have questions and concerns about its costs, resource needs and possible side effects. It’s important to properly engage communities and take their concerns seriously, presenters at the workshop said.
That’s a lesson scientists have learned from their work on other emerging technologies, such as carbon dioxide removal and certain forms of geoengineering, said presenter Shuchi Talati, founder of the nonprofit Alliance for Just Deliberation on Solar Geoengineering. Concerned communities — particularly those that are already disproportionately vulnerable to the effects of climate change and other environmental risks — are not always adequately included in public engagement efforts.
“Getting to this idea of public engagement or participation as a core component of governance is incredibly important,” she said.
More broadly, it’s also important for decisionmakers to clarify the role that methane removal is intended to serve in the larger suite of climate action tools, said presenter Emily Grubert, a civil engineer and environmental sociologist at the University of Notre Dame.
Methane removal one day could be viewed as a kind of carbon offset, a carbon credit that can be sold to fossil fuel emitters to allow them to continue burning fossil fuels into the future. In extreme scenarios though, that could lead to bad-faith activities by fossil fuel emitters, one expert warned.
Oil production, for instance, produces methane as a byproduct. Oil producers burn excess methane to convert it to less potent carbon dioxide in a process known as flaring. Malfunctioning flares can allow excess methane to seep into the atmosphere.
But if methane removal becomes a lucrative part of the carbon offset industry, and it isn’t carefully regulated, fossil fuel companies could choose not to repair malfunctioning infrastructure, Grubert suggested. They could instead allow the gas to escape, conduct removal on site to capture large quantities of methane, and then sell the captured methane as a removal credit.
“That’s a bad case outcome, but that’s the kind of thing that governance may create incentives for if it’s not really, really conscious of a lot of these issues,” she said.
These are issues the forthcoming NASEM report is expected to address. The committee is continuing to accept technical information from scientists through Oct. 31, and the final report likely will be released next summer.
“This is fun, this is novel, this is new,” said Gabrielle Dreyfus, chair of the NASEM committee that’s developing the new report. “But it is not easy.”
