Table 1.
Changing characteristics of the total and anthropogenic terrestrial N2O flux at the beginning of the anthropocene (1850) and through the past century
| 1850 | 1940 | 1980 | 2020 | ||
|---|---|---|---|---|---|
| Total soil flux | Tg N2O-N a−1 | 5.3 ± 0.4 | 6.3 ± 0.5 | 8.7 ± 0.6 | 12.4 ± 0.8 |
| Natural soil flux | Tg N2O-N a−1 | 5.3 ± 0.4 | |||
| Anthropogenic soil emissions | Tg N2O-N a−1 | 0 | 1.0 ± 0.7 | 3.4 ± 0.7 | 7.1 ± 0.9 |
| Growth rate of emissions | Gg N2O-N a−1 a−1 | 19 ± 10 | 23 ± 0.1 | 60 ± 5 | 134 ± 6 |
| Nat. soil emissions—deposition N | Tg N2O-N a−1 | 0.5 ± 0.1 | |||
| Nat. soil emissions—fixation N | Tg N2O-N a−1 | 4.7 ± 0.5 | |||
| Anth. soil emissions—fertilisation N | Tg N2O-N a−1 | 0 | 0.1 ± 0.1 | 0.9 ± 0.2 | 1.7 ± 0.4 |
| Anth. soil emissions—deposition N | Tg N2O-N a−1 | 0 | 0.7 ± 0.1 | 1.8 ± 0.2 | 3.6 ± 0.3 |
| Anth. soil emissions—fixation N | Tg N2O-N a−1 | 0 | 0.2 ± 0.6 | 0.7 ± 0.7 | 1.8 ± 0.6 |
| Anth. emissions not from soils | Tg N2O-N a−1 | 0 | 1.0 ± 0.7 | 1.4 ± 0.7 | 1.7 ± 0.9 |
| δ15N, natural soil emissions | ‰ | −22.4 ± 2.7 | |||
| δ15N, anthrop. soil emissions | ‰ | NA | −15.3 ± 1.1 | −17.0 ± 1.1 | −18.7 ± 1.1 |
| δ15NSP, natural soil emissions | ‰ | 6.7 ± 0.6 | |||
| δ15NSP, anthrop. soil emissions | ‰ | NA | 5.9 ± 0.2 | 6.0 ± 0.2 | 6.8 ± 0.2 |
| EF, area-weighted | % | 1.1 ± 0.1 | |||
| EF, N input-weighted | % | 3.6 ± 0.7 | 3.8 ± 0.7 | 4.0 ± 0.8 | 4.3 ± 0.3 |
The natural flux and the area-weighted emission factors (EFs) do not vary temporally. Growth rate is the 10-year mean growth rate centred on the year of interest, ie. the 10-year average for 2000 is the average from 1995-2005. The area-weighted EF is the mean global EF calculated using the areas of grid cells as weights; the N-input weighted EF is calculated using the total N inputs of grid cells as weights.