NEW YORK—As scientists, policymakers and environmental advocates seek to accelerate efforts to address climate change, they’re zeroing in on a pollutant long considered the “forgotten greenhouse gas.” 

The third-largest driver of climate change and the leading source of atmospheric ozone depletion,

nitrous oxide was center stage Wednesday night at Climate Week, one of the world’s largest annual events dealing with the climate crisis. The N2O talk, at New York University, focused on the growing impacts of that pollution and the potential levers that could be pulled to curb it.   

The presentations came amid ongoing bilateral discussions between the U.S. and China—countries that collectively account for about a quarter of the world’s N2O pollution—on how to reduce these emissions.

“This is about meeting a moment that nitrous oxide has finally had in terms of both the policy and scientific interest in it,” said David Kanter, an environmental studies professor at NYU and co-chair of a global assessment on nitrous oxide by the United Nations’ Climate and Clean Air Coalition scheduled to be released next month.

Nitrous oxide accounts for just five percent of current warming. However, the gas is incredibly potent, 273 times worse than carbon dioxide as a greenhouse gas on a pound for pound basis, and emissions of it are rapidly rising.

“They’re not only going up, but they’re going up even faster than we expected, faster than even the worst-case scenario,” said Drew Shindell, an earth science professor at Duke University and a co-author of the upcoming nitrous oxide report.

Reducing nitrous oxide emissions could prevent 20 million premature deaths worldwide by mid-century, the researchers noted. However, if N2O emissions continue to increase, the added pollution could reverse all progress made in recent decades on restoring concentrations of atmosphere ozone, which protects Earth from harmful ultraviolet radiation, Kanter said.

By mid-century, N2O could also be the leading driver of climate change as efforts to rein in carbon dioxide and methane, now the top drivers, take hold.

The Montreal Protocol, a binding international environmental agreement that has successfully curbed the production and use of other ozone-depleting substances, could be expanded to include nitrous oxide. Tad Ferris, senior counsel at the Institute for Governance and Sustainable Development, an environmental organization based in Washington, D.C., made that case during a brief presentation at the event for incorporating N2O into the Montreal Protocol.

Mumukshu Patel, the senior director of food and agriculture for Climate Advisers, a Washington-based environmental organization, would also like to see a voluntary agreement on nitrous oxide similar to the recent Global Methane Pledge. For that commitment, more than 150 countries said they would reduce methane emissions to address climate change.

The majority of nitrous oxide pollution comes from the agriculture sector, where most emissions are tied to the use of nitrogen-based fertilizer. Reducing emissions from this sector often requires using less fertilizer more efficiently, something that can be difficult to do without jeopardizing food security.

“We have a lot of work to do to develop the technology that allows us to address those emissions at more affordable costs,” said Eric Davidson, an environmental science professor at the University of Maryland.

However, industrial emissions, where nitrous oxide is an unwanted byproduct in chemical production, could be addressed at little cost with proven technology.

“It’s low-hanging fruit because the technology is already there,” Davidson said. “There is really no reason why we can’t essentially limit those emissions to practically zero.”

Davidson noted that most developed countries have already reduced their nitrous oxide emissions from the industrial sector and that the German government is assisting developing countries in doing so.

The two exceptions are the United States and China, which together are responsible for approximately 80 percent of the world’s nitrous oxide emissions from the industrial sector. The emissions come primarily from the production of adipic acid, a precursor to high-strength nylon, and nitric acid, used in fertilizer production.

The nitrous oxide emissions from chemical plants in China and the U.S. were the focus of a 2020 investigation by Inside Climate News. 

“It’s really up to the U.S. and China right now to get their act together and abate those industrial emissions,” Davidson said.  

Producers of adipic acid and nitric acid in Europe and elsewhere have reduced nitrous oxide emissions by 99 percent or more through incineration or chemical breakdown. Installing similar pollution controls at a limited number of chemical plants in China alone could reduce greenhouse gas emissions by up to 200 million tons of carbon dioxide equivalent per year, according to the U.S. deputy special envoy for climate, Rick Duke. The climate impact would be similar to shutting down 50 coal-fired power plants or taking nearly 50 million cars off the road.

“There’s a lot that we do know how to do on addressing industrial N2O,” Duke said during closing remarks at the NYU event. “We clearly need to pick up the pace on addressing this.”

Duke noted that recent commitments from U.S. chemical manufacturers announced at a summit on climate super pollutants at the White House in July put the U.S. on a path to cut its industrial nitrous oxide emissions in half by early next year.

The emissions reductions are voluntary and incentivized through carbon markets. Avipsa Mahapatra, climate campaign director for the Environmental Investigation Agency U.S., a nonprofit based in Washington, said the emissions reductions should be mandatory.

“There is really no excuse to not have a regulatory approach for easily avoidable emissions,” Mahapatra said.

Duke and John Podesta, Biden’s senior advisor for international climate policy, traveled to Beijing in late August and early September to continue bilateral discussions with China to reduce methane and other “non-CO2” greenhouse gases, including nitrous oxide.

“We are deep in conversation with China,” Duke said. “We will continue to push for rapid progress to reduce those emissions.”

Following the visits, China’s Ministry of Ecology and Environment held a workshop on opportunities to address nitrous oxide emissions, including industrial pollution.

Duke noted that the U.S. and China will host a non-CO2 super-pollutant summit at COP29, the U.N. climate summit in Baku, Azerbaijan, in November.

For climate scientists who have long known of the impact of nitrous oxide pollution, the newfound focus by policymakers offers reasons for cautious optimism.

“Hopefully following this kind of moment for N2O, there will be some tangible progress,” Shindell of Duke University said.