This rise is strongly linked to an increase in nitrogen substrates released to the environment. Since the mid-20th century, the production of nitrogen fertilisers, widespread cultivation of nitrogen-fixing crops (such as clover, soybeans, alfalfa, lupins, and peanuts), and the combustion of fossil and biofuels have increased enormously the availability of nitrogen substrates in the environment.

“The increased nitrogen availability has made it possible to produce a lot more food,” Thompson said. “The downside is, of course, the environmental problems associated with it, such as rising N2O levels in the atmosphere.”

Rate of increase of N2O has been underestimated

The study authors found that N2O emissions increased globally to approximately 10 per cent of the global total between 2000-2005 and 2010-2015. This is about twice the amount reported to the United Nations Framework Convention on Climate Change (IPCC) based on the amount of nitrogen fertiliser and manure used and the default emission factor specified by the IPCC. 

The researchers argue that this discrepancy is due to an increase in the emission factor (that is, the amount of N2O emitted relative to the amount of N-fertiliser used) associated with a growing nitrogen surplus.