Effects of Increases in Atmospheric CO₂ and Nitrogen Deposition on the Productivity of the Terrestrial Biosphere

"To investigate feedbacks between climate, atmospheric CO₂, atmospheric nitrogen deposition and carbon uptake of the land over almost two centuries [1860-2030]," Churkina et al. (2009) say they coupled "an earth system model of intermediate complexity" with "a biogeochemical process model" that they used with a "carbon and nitrogen allocation routine" that was "parameterized for seven vegetation types" that included "deciduous broadleaf forest, evergreen needleleaf forest, evergreen broadleaf forest, evergreen deciduous forest, shrubland, C₄ and C₃ grasslands," where they initialized the system by running the model "to a steady state to obtain the size of the ecosystem's carbon and nitrogen pools" under the assumption the ecosystem was "in equilibrium with the long-term climate," utilizing "daily climate data from NCEP Reanalysis for 1968-1977, constant preindustrial atmospheric nitrogen deposition, and CO₂ concentration." So what did they find?

Churkina et al. first determined that their global- and continental-scale estimates of land carbon uptake in the 1990s were "consistent with previously reported data." This comparison with the real world gave them confidence in the results their modeling exercise projected for the future, namely, that "increasing nitrogen deposition and the physiological effect of elevated atmospheric CO₂ on plants have the potential to increase the land carbon sink, to offset the rise of CO₂ concentration in the atmosphere, and to reduce global warming." More specifically, they found that predicted changes in climate, CO₂ and nitrogen deposition for the year 2030 were sufficient to offset atmospheric CO₂ by a sizable 41 ppm. And if likely land use changes were included in the calculations, the offset rose to a huge 76 ppm. Considering these findings, the six scientists who conducted the work, say their study suggests that "reforestation and sensible ecosystem management in industrialized regions may have larger potential for climate change mitigation [italics added, which they equate with buying time] than anticipated [italics added, which they equate with currently thought]."