Atmospheric scientists have warned that a suggested ‘geoengineering’ technique aimed at removing methane—a highly potent greenhouse gas—from the atmosphere could actually worsen air quality and only deliver marginal benefits for the climate.
With greenhouse gases from human activities continuing to accumulate in the atmosphere, various geoengineering solutions have emerged. These aim to modify the atmosphere on a global scale to lower the concentration of carbon or diminish its warming impact.
One recent idea involves infusing the atmosphere with hydrogen peroxide, claiming it would oxidize methane (CH4), a powerful greenhouse gas, while supposedly enhancing air quality.
Is it too good to be true?
University of Utah atmospheric scientists Alfred Mayhew and Jessica Haskins were doubtful and decided to investigate the validity of this proposal. Their findings, published on January 3, confirmed their concerns and provided important insights for organizations weighing such approaches to combat climate change.
“Our research demonstrated that the effectiveness of the proposed technology was quite limited, meaning that broad implementation would be necessary to achieve a significant reduction in atmospheric CH4,” stated Mayhew, a postdoctoral researcher at the university’s Wilkes Center for Climate Science & Policy. “Furthermore, our findings suggest that scaling up this technology could lead to negative air quality effects, especially concerning wintertime particulate matter pollution.”
To carry out the study, the Utah researchers modeled a scenario in which a Canadian company’s patented technology sprays aerosolized hydrogen peroxide (Hâ‚‚Oâ‚‚) into the atmosphere during daylight from 600-meter tall towers—nearly as tall as the world’s tallest radio towers.
“When hydrogen peroxide is exposed to sunlight, it generates a powerful oxidant called the hydroxyl radical OH,” explained Haskins, an assistant professor of atmospheric sciences. “This acts as a natural cleanser in the atmosphere and accelerates the conversion of methane into COâ‚‚.”
Methane is a single-bonded molecule made of carbon and hydrogen, unlike more common double-bonded compounds in the atmosphere. Hydroxyl radicals are more efficient at oxidizing those double-bonded molecules, such as isoprene from trees or volatile organic compounds, which makes OH not very effective for breaking down methane, according to Haskins.
“OH doesn’t react quickly with methane,” Haskins stated. “It reacts with a multitude of other substances.”
The significant impact of methane on climate
While carbon dioxide from fossil fuels receives much of the blame for climate change, methane is also a major contributor. Eventually, methane decomposes into carbon dioxide and water.
The main component of natural gas used in home appliances and power generation, methane (CH4) possesses a climate-warming effect that is 76 times stronger than carbon dioxide over a period of 20 years. Although methane remains in the atmosphere for only 12 years, it has been responsible for about one-third of the rise in global temperatures since the Industrial Revolution, according to the International Energy Agency.
Human activities, particularly those involving oil, gas, coal operations, and landfills, account for 60% of global methane emissions.
While hastening methane oxidation might help mitigate climate change, such geoengineering efforts could lead to negative environmental consequences, a focus of Haskins’s lab. A recent report from the National Academy of Sciences stated that the unintended side effects of removing atmospheric methane are likely considerable but not well understood. Haskins’ research aligns with the report’s call for thorough examination of technologies like the one utilizing significant amounts of hydrogen peroxide.
“This approach might buy us about 50 years and alleviate some immediate climate change effects, yet no one had previously investigated potential side effects,” Haskins remarked. “This paper represents the first study to evaluate any air quality repercussions from such geoengineering methods.”
Possible side effects of geoengineering
Altering a system as intricate as Earth’s atmosphere carries inherent risks that could lead to unexpected issues.
“There are numerous feedback loops within the climate system. Atmospheric chemistry is just one area. Altering one factor may yield anticipated results in one area while producing the opposite effect elsewhere,” Haskins cautioned. “We need to proceed with caution and conduct these types of evaluations. Is this a prudent action? What will the consequences be?”
For example, Haskins highlighted the concerning legacy of human-made gases known as chlorofluorocarbons (CFCs), which depleted the protective ozone layer vital for shielding Earth from harmful UV radiation.
“The use of CFCs in industries as propellants and refrigerants led to the creation of the ozone hole,” she noted. “We’ve dealt with the fallout from that for 40 years, and we likely won’t see a fully resolved ozone situation until around 2060, so we must be careful about our actions.”
Mayhew and Haskins leveraged a global chemical-transport model, called GEOS-Chem, to simulate the proposal of releasing hydrogen peroxide from towers. Their goal was to predict the extent of methane oxidation under three different emission scenarios, ranging from low to high.
Their simulation imagined deploying 50 towers across North America. Following the company’s plan, the medium-release scenario involved each tower spraying 612 grams (1.35 pounds) per second for 10 hours daily throughout the year.
“This proposed method simply won’t eliminate any significant amount of methane from the atmosphere. It won’t resolve global warming either. At most, our findings showed that 50 towers could reduce only 0.01% of annual human-related methane emissions,” Haskins explained. “You would require around 352,000 of these towers to remove 50% of anthropogenic methane. That’s an absurd figure. Even with 50 high-emission towers, it would still take about 43,000.”
Meanwhile, areas with already poor air quality during winter could experience even worse particulate pollution.
“Future research could indicate that the air quality ramifications of placing these towers near methane emission sources are minimal if operated at specific times of the year and distanced from large populations,” Mayhew noted. “If that holds true, then this technology (or similar ones) could have a very minor role in combating warming, but it’s evident from our research that the air quality consequences should be a primary consideration in any real-world applications of such technology.”
