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Emissions of Super-Pollutant Nitrous Oxide Rising on ‘Worst-Case’ Trajectory

Global emissions of nitrous oxide (N2O) are rising on a frightening scale, putting them on track to single-handedly push global warming far beyond the limits of the Paris Agreement, according to a new study.

The alarming trend has experts calling for new and adapted policies that can expand the focus on emissions beyond carbon dioxide, InsideClimate News reports.

“Emissions of nitrous oxide, a climate super-pollutant hundreds of times more potent than carbon dioxide, are rising faster than previously thought—at a rate that not only threatens international targets to limit global warming, but is consistent with a worst-case trajectory for climate change,” InsideClimate says. The study, which is “arguably the most comprehensive assessment of the global nitrogen cycle ever conducted,” was published last week in the journal Nature.

While N2O “is responsible for roughly 7% of global warming since preindustrial times,” the researchers found that human-caused emissions of the greenhouse gas “have increased by 30% since 1980,” with much of the increase owing to the overuse or misuse of nitrogen fertilizers. Any fertilizer not taken up by crops converts to N2O, which is 300 times more potent than carbon dioxide as driver of climate change.

In its own coverage of the new research, The Guardian attributes surging use of nitrogen fertilizers over the past 40 years to the cheap, synthetic versions now available in abundance, with “few restrictions on their deployment around the world.”

Should these fertilizers continue to be used without restriction, notes InsideClimate, “the world’s average temperature would rise by approximately 4.3°C above pre-industrial times, far higher than the limit of 1.5 to 2°C of warming targeted in the Paris climate agreement.”

Even current N2O emissions “are not tenable,” warned lead author Hanqin Tian, director of the International Center for Climate and Global Change Research at Auburn University. “The numbers are very large, and the increases are very rapid,” he added.

Citing the success of Europe’s Nitrate Directive, which mandated more efficient use of nitrogen fertilizers and successfully drew down N20 levels without harming crop yields, Tian noted that reducing these emissions will not, as is sometimes proposed, mean food insecurity.

Still, those seeking to regulate N2O emissions in the field will still have to reckon with the pro-fertilizer farm lobby, especially in the developing world.

“The EU system has been partially successful but not a complete success story,” said David Kanter, an environmental studies professor at New York University. Nitrogen water pollution still remains a significant issue in Europe, and, notes InsideClimate, “the Union’s regulatory policies would be difficult to replicate elsewhere.”

Further complicating the issue, N2O emissions may actually be worse than measured in the latest study. InsideClimate recently reported on N2O emissions from 11 plants in China that manufacture adipic acid, “a key ingredient of nylon and polyurethane.” These plants “likely emit hundreds of thousands of tonnes of N2O per year despite proven, low-cost abatement technology that could reduce 95% or more of total emissions,” the Pulitzer-winning climate newsletter wrote.

But all is not yet lost in the fight to reduce emissions.

Seizing on the fact that N2O also poses a significant threat to the health of the ozone layer, experts are urging policy-makers to add the pollutant to the growing list of chemicals now restrained by the Montreal Protocol, a binding international agreement adopted in 1987. Banning N2O would “continue to significantly expand the scope of the protocol, which was recently amended to include hydrofluorocarbons, chemical refrigerants that are both ozone depleters and potent greenhouse gases.”

Past successes of the protocol speak to its potential to avert disaster with N2O, said Durwood Zaelke, president of the Institute for Governance & Sustainable Development.

“It is able to move fast, and it’s been effective with nearly 100 chemicals that it has controlled in the past,” he told InsideClimate. “You’ve got to put your best players into the game, and if we are trying to solve climate change, the best player is the Montreal Protocol.”