Nitrous oxide emissions are enhanced in a warmer and wetter world.

Nitrous oxide (NO) has a global warming potential that is 300 times that of carbon dioxide on a 100-y timescale, and is of major importance for stratospheric ozone depletion. The climate sensitivity of NO emissions is poorly known, which makes it difficult to project how changing fertilizer use and climate will impact radiative forcing and the ozone layer. Analysis of 6 y of hourly NO mixing ratios from a very tall tower within the US Corn Belt-one of the most intensive agricultural regions of the world-combined with inverse modeling, shows large interannual variability in NO emissions (316 Gg NO-N⋅y to 585 Gg NO-N⋅y). This implies that the regional emission factor is highly sensitive to climate. In the warmest year and spring (2012) of the observational period, the emission factor was 7.5%, nearly double that of previous reports. Indirect emissions associated with runoff and leaching dominated the interannual variability of total emissions. Under current trends in climate and anthropogenic N use, we project a strong positive feedback to warmer and wetter conditions and unabated growth of regional NO emissions that will exceed 600 Gg NO-N⋅y, on average, by 2050. This increasing emission trend in the US Corn Belt may represent a harbinger of intensifying NO emissions from other agricultural regions. Such feedbacks will pose a major challenge to the Paris Agreement, which requires large NO emission mitigation efforts to achieve its goals.