Emissions of Nitrous Oxide, a Climate Super-Pollutant, Are Rising Fast on a Worst-Case Trajectory

https://insideclimatenews.org/news/07102020/nitrous-oxide-fertilizer-emissions-nature-study

By Phil McKenna
Oct 7, 2020

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, a new study suggests.

The findings, reported Wednesday in the journal Nature, underscore the need for strong climate policies that do not focus solely on carbon dioxide, the dominant greenhouse gas.

The study, arguably the most comprehensive assessment of the global nitrogen cycle ever conducted, found that nitrous oxide (N2O) emissions caused by human activities have increased by 30 percent since 1980. Those emissions, more than two-thirds of which come from agriculture, account for nearly half of all nitrous oxide released over the past decade, with the rest coming from natural ecosystems.   

Nitrous oxide is the third most important greenhouse gas after carbon dioxide and methane, and is responsible for roughly 7 percent of global warming since preindustrial times. It is nearly 300 times more potent at warming the planet than carbon dioxide, which means that even small sources of emissions can have an outsized impact on the climate. 

Nitrous oxide is also the largest contributor to atmospheric ozone depletion that is not controlled by the Montreal Protocol, an international agreement developed in the 1980s to phase out ozone depleting chemicals through mandatory emissions reductions. Some policy experts say the agreement should now be extended to include nitrous oxide.

Emissions reported in the current study are in line with, or slightly higher than, a "worst case" emissions scenario by the United Nations Intergovernmental Panel on Climate Change. 

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Curbing nitrous oxide emissions is difficult because the vast majority of anthropogenic emissions are driven by the use of nitrogen-based fertilizer, which emits nitrous oxide as it breaks down in the soil if not taken up by plants. Farmers worldwide depend on nitrogen fertilizer to increase crop production.

However, more efficient fertilizer use can curb nitrous oxide emissions. N2O emissions from agriculture in Europe decreased by 21 percent between 1990 and 2010 in response to agricultural policy that favors optimization and reduction of fertilizer use, according to the study. The policy, known as the "Nitrates Directive," was developed to protect European waters from nitrogen pollution, which causes algae blooms and "dead zones" in freshwater and marine environments and occurs when too much nitrogen fertilizer or manure is used. 

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