A New Estimation of Global Soil Greenhouse Gas Fluxes Using a Simple Data-Oriented Model

Soil greenhouse gas fluxes (particularly CO(2), CH(4), and N(2)O) play important roles in climate change. However, despite the importance of these soil greenhouse gases, the number of reports on global soil greenhouse gas fluxes is limited. Here, new estimates are presented for global soil CO(2) emission (total soil respiration), CH(4) uptake, and N(2)O emission fluxes, using a simple data-oriented model. The estimated global fluxes for CO(2) emission, CH(4) uptake, and N(2)O emission were 78 Pg C yr(−1) (Monte Carlo 95% confidence interval, 64–95 Pg C yr(−1)), 18 Tg C yr(−1) (11–23 Tg C yr(−1)), and 4.4 Tg N yr(−1) (1.4–11.1 Tg N yr(−1)), respectively. Tropical regions were the largest contributor of all of the gases, particularly the CO(2) and N(2)O fluxes. The soil CO(2) and N(2)O fluxes had more pronounced seasonal patterns than the soil CH(4) flux. The collected estimates, including both the previous and the present estimates, demonstrate that the means of the best estimates from each study were 79 Pg C yr(−1) (291 Pg CO(2) yr(−1); coefficient of variation, CV = 13%, N = 6) for CO(2), 21 Tg C yr(−1) (29 Tg CH(4) yr(−1); CV = 24%, N = 24) for CH(4), and 7.8 Tg N yr(−1) (12.2 Tg N(2)O yr(−1); CV = 38%, N = 11) for N(2)O. For N(2)O, the mean of the estimates that was calculated by excluding the earliest two estimates was 6.6 Tg N yr(−1) (10.4 Tg N(2)O yr(−1); CV = 22%, N = 9). The reported estimates vary and have large degrees of uncertainty but their overall magnitudes are in general agreement. To further minimize the uncertainty of soil greenhouse gas flux estimates, it is necessary to build global databases and identify key processes in describing global soil greenhouse gas fluxes.