Top-down estimates of N2O emissions over the past two decades

Tuesday, December 11, 2018 - 16:00
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Nitrous oxide (N2O) is the third most important long-lived greenhouse gas and is an important ozone depleting substance. Atmospheric N2O has increased by approximately 20% since the pre-industrial era largely due to human perturbation of the N-cycle. We present global N2O emission estimates from five inverse models. The inversions were run with the user’s own choice of input data and settings for the minimum period of 1995 to 2014. The model results were assessed by comparisons to independent observations and by using a number of diagnostics such as the atmospheric lifetime and the loss of N2O. Posterior emissions were analysed at global and regional scales and compared to independent bottom-up modelling studies. We find broad consistency among the inversions for the global total emission of 16-18 TgN/y and with land ecosystem models for the total land emissions of approximately 10 TgN/y. On the other hand, the inversions find larger ocean emissions, of 6-7 TgN/y, compared to the range from ocean biogeochemistry models of 3-4 TgN/y. Moreover, the inversions show that in regions of high N-input, such as East Asia, N2O emissions increased at a faster rate than the N-inputs, suggesting that the emission response is non-linear or that there has been an accumulation of N in the environment.

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