When we talk about climate change, the culprit is quickly identified: carbon dioxide. But the list of climate-damaging gases is longer and includes, for example, methane and fluorocarbons (CFCs). Currently, researchers are particularly concerned about nitrous oxide (N2O).
According to a study in the journal "Nature Climate Change", it gets into the atmosphere in significantly higher quantities than previously thought.
This is mainly due to the excessive use of nitrogen fertilizer. If nitrogen (N) is not taken up by plants, nitrous oxide can form in the soil, which escapes into the atmosphere. Nitrous oxide is a 300 times more powerful greenhouse gas than carbon dioxide and contributes six to seven percent to the global greenhouse effect. In addition, the substance attacks the ozone layer.
Researchers led by Rona Louise Thompson from the Norwegian Institute of Air Research (NILU) have now evaluated data from a global greenhouse gas monitoring network. They examined how the nitrous oxide concentrations in the atmosphere developed from 1998 to 2016. Result: Since the beginning of industrialization, the atmospheric content has increased from 290 particles per billion air molecules (ppb) to 330 ppb in 2017.
Julian Stratenschulte / DPA
Fertilizer fertilizer Nitrous oxide affects 300 times more on climate than carbon dioxide
Especially in the past 20 years, the N2O concentration rose sharply. In the period from 2000 to 2005, the emissions were still at 16.3 million tonnes of nitrogen in the form of nitrous oxide in the year. From 2010 to 2015, the value reached 17.9 million tons annually. The emissions have increased particularly strongly since 2009, according to the researchers.
IPCC underestimates agriculture's influence on nitrous oxide emissions
In order to determine the impact of fertilization on the growing content of nitrous oxide in the atmosphere, researchers calculated other possible nitrous oxide sources from their data, including industry. According to this, about 2.3 percent of the nitrogen used in fertilizer as laughing gas escaped into the atmosphere.
The IPCC (International Climate Council) estimates that it has a value of 1.4 percent – and has thus considerably underestimated N2O emissions from soils, at least in recent years.
According to the study, agriculture has a particularly large influence on the rising nitrous oxide content in the atmosphere in East Asia and South America. China, in particular, is contributing to rising emissions. But also in India, Nepal, Bangladesh and Brazil, N2O emissions have grown from soils. At the same time, large quantities of fertilizer had been used there, according to the researchers.
Nitrous oxide lingers in the atmosphere for around 120 years
In the US and Europe, on the other hand, nitrous oxide emissions have remained largely stable.
The study increases the importance of nitrous oxide emissions from agriculture for climate protection, explains Fortunat Joos, climate expert at the University of Bern, who was not involved in the study. "The results suggest that nitrous oxide emissions from fertilizer in the national climate reports to the United Nations are around 70 percent too low."
However, it would be difficult to reduce emissions completely because the growing world population had to be fed. The only consolation: nitrous oxide only lingers in the atmosphere for around 120 years. If the emissions stabilize at a low level, the nitrous oxide concentration in the atmosphere also remains stable. By comparison, carbon dioxide stays there for millennia.