Under what is considered a best-case model, global annual emissions of carbon dioxide will have to start declining by 2020 to stabilize atmospheric carbon dioxide at 450 parts per million.
Fire contributions to CO2 variability in the best-case model varied with latitude.
Simultaneously accounting for temperature, drought, and fire in the best-case model improved both goodness-of-fit metrics compared to models that assumed only a single driver.
Moreover, synthetic data generated from the best-case model, as opposed to those from the tropical temperature-only model, were more consistent with the atmospheric observations.
For a best-case model estimate, we optimized λ coefficients for temperature, drought, and fires from the Northern Hemisphere and tropics simultaneously.
Accounting for correlations among successive monthly observations, the calculated F statistic justified the additional degrees of freedom in the best-case model relative to the tropical temperature-only model (p < 0.01).
The sensitivity of tropical NEE to temperature was further reduced to 2.6 ± 0.7 Pg C yr−1 K−1 when we considered all scale factors from the best-case model.
We tested an alternative version of the best-case model, substituting precipitation for PDSI as the climate proxy for drought stress, and regression results indicated a further reduction in the contribution from tropical temperature to CO2 variability.
For the best-case model described above, the tropical fire contribution decreased by 60% when fit against a globally averaged CO2 timeseries rather than against the meridional structure of CO2 (Table 6).
In the Northern Hemisphere, the standard deviation of the fire flux in the best-case model increased to 0.13 ± 0.04 Pg C yr−1 from the GFED3 baseline of 0.10 Pg C yr−1.
In the diffuse ISM, AV/NH ≈ 5.3 × 10−22magcm2 (which, which leads to NH ≈ 7.7 × 1022 cm−2 for our best "CASE B" model extinction curve.
