Humanity is producing more and more climate-damaging nitrous oxide - the third most important greenhouse gas after carbon dioxide and methane, according to a comprehensive analysis published in the United States.
In the four decades since 1980, nitrous oxide emissions caused by humans have increased by around 40%, the Global Carbon Project research network led by Boston College in the north-east US state of Massachusetts showed.
The values were particularly high in the most recently analysed years 2020 and 2021.
Doctors use nitrous oxide, also known as nitrogen monoxide or N2O, as an anaesthetic. As a recreational drug, it's better known as laughing gas. However, much larger quantities are produced accidentally, for example by fertilizing fields or burning fossil fuels, and are thus released into the atmosphere.
Main drivers: chemical fertilizers and manure
Nitrous oxide is also released into the air naturally and, according to the researchers, two thirds of current emissions can be attributed to this. However, this is normally broken down again. Humans have intervened in this natural nitrogen cycle of the earth.
They use the nitrogen in the air - such as N2, not N2O - to produce fertilizer in a chemical process. Added to this is the manure that is left on pastures or spread on fields. If all of this fertilizer is not completely absorbed by the plants, it can be directly converted into nitrous oxide or later indirectly released into the atmosphere.
According to the study, agriculture is now responsible for 74% of human nitrous oxide emissions. Particularly in countries where the population has grown by many millions, nitrous oxide emissions have also risen sharply over the four decades analysed, especially in China and India. In Europe, on the other hand, emissions fell, in part because fewer fossil fuels were used and the chemical industry changed its processes.
Emissions up 25% in the atmosphere
According to Boston College, humanity produced around 10 million tons of nitrous oxide per year in 2020 and 2021. While there were still 270 nitrous oxide particles per billion particles (ppb) in the atmosphere in 1750, just before the industrial revolution, this figure rose to 336 particles in 2022 - an increase of almost 25%.
The authors of the study emphasize that it is necessary to reduce nitrous oxide emissions in order to meet climate targets. Only then can the global temperature rise be limited to two degrees, explained lead author Hanqin Tian from Boston College.
"Reducing nitrous oxide emissions is the only solution, as there are currently no technologies to remove nitrous oxide from the atmosphere."
Emissions can be cut through more targeted fertilization
To reduce the amount of man-made nitrous oxide, experts suggest several approaches. The US Environmental Protection Agency, for example, considers it crucial to use fertilizers more efficiently - if less fertilizer is used, less surplus remains in the soil, which can turn into nitrous oxide.
The agency also recommends using less oil, gas and coal or using catalytic converters when burning them.
The very comprehensive study involved 58 experts from 15 countries, including Europe. They used millions of measurements from four decades: from the air, fresh water and the oceans.
According to Tian, this is the most comprehensive study of global nitrous oxide to date. Due to the large uncertainties, for example with regard to soil conditions, the researchers give a wide range for N2O emissions. The measurements of the N2O content in the atmosphere, on the other hand, are very accurate.
