Greenhouse gases (GHGs) are gases in Earth’s atmosphere that absorb heat radiated from the planet’s surface. Like the glass walls of a greenhouse, they trap heat and prevent it from escaping. There are several types of GHGs, but two are especially well-known: carbon dioxide (CO2) and methane (CH4). There’s also a GHG called nitrous oxide (N2O) that’s better known as “laughing gas”. Like methane, it’s sometimes blamed (unfairly) on cows.
What’s So Funny about Nitrous Oxide?
Nitrous oxide is called “laughing gas” because inhaling it can produce a euphoric feeling that leads to uncontrollable laughter. Its main applications aren’t for entertainment, however. Medically, N2O is used as a sedative and analgesic, especially in dentistry. It’s also used as a propellant in whipped cream dispensers, an oxidizer in rocket propulsion, and to increase engine performance in racing.
Nitrous oxide also has an important relationship with agriculture. Farmers who want to increase crop yields may apply chemical fertilizers to stimulate microbial activity. In turn, these soil microbes make nutrients and minerals in the soil available to plants. In aerobic or oxygen-rich conditions, soil bacteria convert ammonium to nitrate. Nitrous oxide is a byproduct of this process.
Under anaerobic or low-oxygen conditions, soil bacteria reduces nitrate to gases that include N2O. Typically, this happens in waterlogged soils. Yet nitrous oxide is also found in animal manure as it decomposes. Whether it’s stored in piles or lagoons or directly applied to fields, manure releases nitrogen compounds that are converted to N2O.
By and large, however, the U.S. EPA cites Agricultural Soil Management – and not Manure Management – as the main source of nitrous oxide emissions.
Comparing GHGs: GWP and Longevity
Nitrogen oxide is far less abundant in the atmosphere than carbon dioxide or methane. However, N2O’s global warming potential (GWP) is 265 times that of carbon dioxide over a 100-year time scale. What some studies fail to mention, however, is that nitrous oxide emissions remain in the atmosphere for an average of 100+ years. Whether that’s a long time or not depends on how you look at it.
Carbon dioxide, the most prevalent GHG, remains in the atmosphere between 300 and 1000 years. That’s between 3 to 10 times longer than nitrous oxide. Methane, a GHG that comes in part from the digestive process of cows, remains in the atmosphere for just 7 to 12 years. It has a GWP that’s ten times less that of nitrous oxide.
What Does the Data Really Show?
Nitrous oxide isn’t as well-known as carbon dioxide or methane, but N2O emissions grew 40% from 1980 to 2020. That’s faster than at any other time in human history. The Global Carbon project describes Agriculture as the leading anthropogenic or manmade source but does not break out chemical fertilizers vs. manure vs. the burning of diesel fuel in agriculture equipment (which also produce N2O).
Then there’s the fact that a large portion of N2O emissions come from natural sources rather than manmade ones. As the Global Carbon Project’s data shows, Open Oceans produce almost as much N2O as Agriculture. So-called Natural Soils produce even greater amounts of N2O. For those who are eager to blame cows, what does the data really show?