Table 1.
Simulated trace greenhouse gases in early Eocene (55 Ma) and late Cretaceous (90 Ma) atmospheres
| [CH4] (ppb) | CH4 lifetime (yrs) | ΔH2O[strat] (%/ppm) | [surface O3] (ppb) | [OH] (ppt) | [N2O] (ppb) | |
| Simulation | ||||||
| Preindustrial (PI, 0 Ma) | ||||||
| 1 × CO2 (280 ppm) | 695 (635–700) | 7.1 | not applicable | 11.8 | 0.05 | 278 (275–280) |
| Early Eocene (55 Ma) | ||||||
| 2 × CO2 (560 ppm) | 2,580 | 7.9 | +25%/1.5 ppm | 17.7 | 0.039 | 373 |
| 2 × CO2 (PI isoprene flux) | 2,384 | 7.2 | 15.7 | 0.043 | 373 | |
| 4 × CO2(1,120 ppm) | 3,614 | 7.8 | +40%/3.0 ppm | 19.3 | 0.035 | 323 |
| 4 × CO2 (PI isoprene flux) | 3,305 | 7.1 | 16.8 | 0.040 | 323 | |
| Late Cretaceous (90 Ma) | ||||||
| 4 × CO2 (1,120 ppm) | 3,304 | 9.1 | +40%/3.0 ppm | 20.1 | 0.036 | 426 |
Values are for the troposphere unless otherwise indicated. Values are annual means for the last 12 months of each simulation after reaching equilibrium. Increases in stratospheric water vapor at an altitude of 40–50 km were estimated from two-dimensional chemical transport model calculations (27) with a surface methane concentration of 3,400 ppb, and are given as both a % and absolute increase, relative to the PI. N2O is unreactive in the troposphere, with a long atmospheric lifetime of approximately 150 years (2). Tropospheric N2O concentrations are calculated from the sum of the sources (from soils and biomass burning) and sinks and a 1D atmospheric model (see SI Text, SI Methods). Values in parentheses under the PI results indicate independent estimates (2).