Global N2O Budget Synthesis

Important new synthesis papers have come forth in 2019 and 2020 on the human impacts of the global nitrous oxide (N2O) budget. 

Most of us know nitrous oxide as “laughing gas,” used for its anesthetic effects. But nitrous oxide (N2O) is actually the third most important long-lived greenhouse gas, after carbon dioxide (CO2) and methane. Nitrous oxide is also one of the main stratospheric ozone depleting substances— and we are releasing more of it into the atmosphere than previously thought.

Aerial photograph of cropland in AsiaIn a paper published in Global Change Biology (DOI: 10.1111/gcb.14514), Tian et al. assessed the effects of multiple anthropogenic and natural factors, including nitrogen (N) fertilizer application, atmospheric N deposition, manure N application, land cover change, climate change, and rising atmospheric CO2 concentration, on global soil N2O emissions for the period 1861–2016 using a standard simulation protocol with seven processbased terrestrial biosphere models.

The Tian et al. (2019) paper was followed by another in Nature Climate Change (https://doi.org/10.1038/s41558-019-0613-7) by Thompson et al, (2019) that uses inversions of observations of atmospheric concentrations of N2O to deduce spatial and temporal variation of sources from oceans and the continents.

“We see that the N2O emissions have increased considerably during the past two decades, but especially from 2009 onwards,” said lead scientist Rona L. Thompson from NILU–Norwegian Institute for Air Research. “Our estimates show that the emission of N2O has increased faster over the last decade than estimated by the Intergovernmental Panel on Climate Change (IPCC) emission factor approach.”

This new publication demonstrates both how we can solve a problem of growing greenhouse gas emissions and how current efforts are falling short in some regions of the world. In Europe and North America, we have succeeded in decreasing growth in nitrous oxide emissions, an important contributor to climate change and stratospheric ozone depletion. Unfortunately, the same can’t be said for Asia and South America, where fertilizer use, intensification of livestock production, and the resulting nitrous oxide emissions are growing rapidly.

Most recently, a third important paper, with an author group overlapping with the Tian et al. (2019) and Thompson et al. (2019) papers was published in Nature (Tian et al., 2020. https://doi.org/10.1038/s41586-020-2780-0). This work, which is part of the Global Research Project of FutureEarth and a Research Partner of the World Climate Research Programme, synthesizes the process-based modeling (Tian et al. 2019), atmospheric inversion modeling (Thompson et al. 2019), and additional inventory data to generate a comprehensive global nitrous oxide budget (see figure). Unfortunately, while it shows some progress in some regions and economic sectors, it reveals overall lack of mitigation of this important greenhouse gas at the global scale. It highlights the need for redoubled efforts to reduce emissions and subsequent increases in atmospheric N2O. A companion article published in The Conversation presents an overview of the findings of Nature paper for a general audience: https://theconversation.com/new-research-nitrous-oxide-emissions-300-times-more-powerful-than-co-are-jeopardising-earths-future-147208#:~:text=As%20a%20greenhouse%20gas%2C%20N%E2%82%82O,in%20the%20atmosphere)%20and%20methane.

This work is also featured in a seminar presented by Dr. Davidson at the Appalachian Laboratory’s Fall 2020 Seminar Series.

Infographic summarizing the global nitrous oxide budget.

Crop photo by Ibadah Mimpi from Pexels