Nitrous Oxide
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Nitrous Oxide, The Shunned Stepchild of the Greenhouse Gas Family

CO2, Methane, and The Other One

Recently a spat of news reports highlighted the role of methane in promoting global warming. COP26 got in on the action with various commitments to reduce methane emissions from sources as varied as oil wells to belching cows. Methane has caught people’s interest because it has about 80 times the warming power of its puny brother, carbon dioxide. But there is a third and nastier sibling, nitrous oxide, with a warming capacity equal to about 300 times that of CO2.

Some of you may recognize nitrous oxide (N2O) by its more common name, ‘laughing gas.’ Yes, the friendly little guy giving many of us a delightful ride in the dentist’s chair leads a double life as a mean-ass climate warmer. It’s like a child walking into the post office with Mom and seeing their sweet babysitter’s face on a most wanted poster.

But nitrous oxide appears in places other than the dentist’s office. Enough of it collects in the atmosphere to make it the third most prevalent greenhouse gas, accounting for about six percent of global greenhouse gas emissions. But burning fossil fuels is not at the heart of the N2O problem. Agriculture is the main culprit, accounting for roughly three-quarters of all N2O emissions.

The Greenhouse Emissions Family

When we line up all the siblings in order of annual emissions, we get the following:

Carbon Dioxide — 76%

Methane — 16%

Nitrous Oxide — 6%

The remaining 2% is from fluorinated gases

These rankings are based on measurements of tons of CO2 equivalent. For example, one ton of N2O has the warming potential of 298 tons of CO2, so its CO2 equivalent weight is 298 tons when, in reality, only a single ton has been emitted — presenting the data this way lets us see the percentage of warming caused by each gas. Additionally, water vapor is not included in the list since it is a condensable greenhouse gas.

Nitrous Oxide packs quite a punch, and its primary origin in the agricultural sector makes controlling these emissions a challenge. A factory dumping out tons of greenhouse gases creates a point-source problem where large, concentrated emissions can be addressed at a single location. When the problem spreads across millions of acres of farmland, there is no single point to focus on.

The problem of nitrous oxide emissions has been generally ignored in our efforts to combat climate change, even though we have seen a 30% increase in N2O emissions over the past four decades. It is easier to make large oil companies the bad guys than point a finger at farmers. After all, we all want to have reasonably priced food. The main culprit for rising N2O emissions is a global addiction to synthetic nitrogen fertilizer.

How Does Happy Gas Form?

Understanding the nitrous oxide problem requires knowing how it forms. The processes producing this gas are part of the earth’s nitrogen cycle. Since plants arrived on the planet, N2O emissions have formed part of the natural cycle of growth and nutrient use. Overuse of synthetic nitrogen fertilizers puts the natural cycle into hyperdrive and creates the problem we face today.

Before modern fertilizers, plants received their nitrogenous nutrients when bacteria in compost (think manure) took in N2 from the air and converted it to ammonium, a soluble nutrient that plants absorb through their root systems. If plants don’t absorb all the ammonium, then bacteria and microbes in the soil convert it first to nitrate and then back into N2 gas, which re-enters the atmosphere. A byproduct of processing the excess ammonium is nitrous oxide.

In an ideal world, the amount of synthetic nitrogen fertilizer used in farming would match the amount of ammonium required for healthy crops. Since achieving this delicate balance is difficult, the tendency is to over-fertilize, ensuring healthy high-yield crops, but also ensuring increased N2O emissions.

Various precision farming options are under investigation to decrease N2O emissions from agriculture, but until they gain widespread acceptance and are economically competitive, the current practice of over-fertilizing will continue to drive rising N2O emissions.

Elected officials naturally shrink from policies that have a negative impact on food prices. Voters, it seems, want to put reasonably priced food on their dinner tables. But more happy gas will not lead to happier outcomes on the climate change front. The ideal technological solutions will need to provide farmers with lower-cost options than their current farming practices. The good news is, scientists are working on solutions that may fulfill this goal.


Related Articles:

Cows, up to environmental mischief again (by WM House; ArcheanWeb)

Cows Belch Methane, So Does the Earth (by WM House; ArcheanWeb)

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Sources:

Overview of Greenhouse Gases (Source EPA)

The world’s forgotten greenhouse gas (by Ula Chrobak; BBC)

Stanford expert explains why laughing gas is a growing climate problem (by Josie Garthwaite; Stanford News)

William House
William is an earth scientist and writer with an interest in providing the science "backstory" for breaking environmental, earth science, and climate change news.