133 Sensitivity of Nitrous Oxide Emissions to Climate

Wednesday, 22 June 2016
Alta-Deer Valley (Sheraton Salt Lake City Hotel)
Timothy J. Griffis, University of Minnesota, St Paul, MN; and Z. Chen, J. D. Wood, J. M. Baker, P. Turner, X. Lee, and D. B. Millet

Production of synthetic nitrogen (N) fertilizer is forecast to exceed 200 Tg N in 2018— a 25% increase since 2008. The current trajectory of global N fertilizer production is following one of the most aggressive scenarios considered by the Food and Agricultural Organization of the United Nations. Regional and global analyses demonstrate that about 4.5% of the anthropogenic N (fertilizer, deposition, manure) in agricultural systems is returned to the atmosphere as nitrous oxide (N2O)—a potent greenhouse gas and ozone-depleting substance. While growing population and demands for food, fiber, and fuel are accelerating the use of synthetic N, it remains unclear how sensitive N2O emissions are to climate variations. In this study, six years of hourly N2O concentration measurements from a very tall tower located within the US Corn Belt were used within a Bayesian inverse modeling framework to estimate the inter-annual variability in regional N2O emissions. The variability in emissions was large, ranging from 315 to 555 Gg N2O-N y-1 (mean = 386 +/- 105 Gg N2O-N y-1) with a coefficient of variation of 27%. The sensitivity of emissions to climate variability was assessed by considering: 1) the response of direct and indirect emissions to climate drivers; and 2) by examining the seasonal and episodic fluctuations in tall tower concentrations to climate drivers using wavelet coherence analyses. These analyses were used to compute climate sensitivity factors for N2O emissions. They indicate that precipitation (timing, frequency, and magnitude) and surface runoff are key regional drivers that cause large fluctuations in the indirect emissions. State-of-the-art land surface schemes did not accurately capture the seasonal and inter-annual variability in N2O emissions, suggesting that the sensitivity of key model processes to climate variations is poorly constrained. The implications of increasing production of synthetic nitrogen and current climate trends on future N2O emissions will be discussed.
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