A gap in nitrous oxide emissions reporting complicates long-term climate mitigation

Authors: Del Grosso, Stephen - Steve; OGLE, STEPHEN - Natural Resource Ecology Laboratory; NEVISON, CYNTHIA - Colorado State University; GURUNG, RAM - Indigo Ag; PARTON, WILLIAM - Colorado State University; WAGNER-RIDDLE, CLAUDIA - University Of Guelph; SMITH, WARD - Agriculture And Agri-Food Canada; WINIWARTER, WILFRIED - International Institute For Applied Systems Analysis; GRANT, BRIAN - Agriculture And Agri-Food Canada; TENUTA, MARIO - University Of Manitoba; MARX, ERNIE - Colorado State University; SPENCER, SHANNON - Colorado State University; WILLIAMS, STEPHEN - Colorado State University

Submitted to: Proceedings of the National Academy of Sciences (PNAS)
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/1/2022
Publication Date: 7/25/2022
Citation: Del Grosso, S.J., Ogle, S., Nevison, C., Gurung, R., Parton, W., Wagner-Riddle, C., Smith, W., Winiwarter, W., Grant, B., Tenuta, M., Marx, E., Spencer, S., Williams, S. 2022. A gap in nitrous oxide emissions reporting complicates long-term climate mitigation. Proceedings of the National Academy of Sciences(PNAS). 119(31). Article e2200354119. https://doi.org/10.1073/pnas.2200354119.
DOI: https://doi.org/10.1073/pnas.2200354119

Interpretive Summary: Efforts to quantify greenhouse gas emission reductions needed to achieve climate targets such as those formulated in the Paris Agreement (and to share the efforts fairly between countries) need to be based on the best available science. Here we demonstrate that, for the United States, ecosystem models can account for soil, plant and fertilization conditions to quantify the emissions of nitrous oxide (N2O), and adequately cover observed large pulses due to soil freezing and thawing events. For their national reports to the climate convention, most other countries rely on a simple linear approach. While sufficient to estimate CO2 emissions, ongoing efforts to curb other important greenhouse gases and the need of agricultural intensification without extra emissions will require more accurate N2O inventories.

Technical Abstract: Nitrous oxide (N2O) is an important greenhouse gas (GHG) that also contributes to depletion of ozone in the stratosphere. Agricultural soils account for about 60% of anthropogenic N2O emissions. Most national GHG reporting to the UN Framework Convention on Climate Change assumes nitrogen (N) additions drive emissions during the growing season, but soil freezing and thawing during spring is also an important driver in cold climates. We show that both atmospheric inversions and newly implemented bottom-up modeling approaches exhibit large N2O pulses in the northcentral region of the United States during early spring and this increases annual N2O emissions from croplands and grasslands by 11% nationwide. Considering this, emission accounting in cold climate regions are very likely under-estimated in most national reporting frameworks. Current commitments related to the Paris Agreement and COP 26 emphasize reductions of carbon compounds. Assuming these targets are met, the importance of accurately accounting and mitigating N2O increases once CO2 and CH4 are phased out. Hence, the N2O emission under-estimate introduces additional risks into meeting long term climate goals.