Biosphere Carbon Balance

In addition to atmospheric and oceanic pools of carbon, the FeliX model tracks terrestrial carbon stocks in the biosphere and humus. Atmospheric carbon concentrations are linked logarithmically to the net primary productivity (NPP) of the biosphere, a measure of carbon uptake due to plant growth:

FeliX equation for net primary productivity NPP(t) [PgC/year], an expression of the annual biospheric uptake of atmospheric carbon. NPP' represents initial (ca. 1900) net primary productivity and is equal to 85.2 PgC/year. A dimensionless biostimulation coefficient ε = 0.35, describes the impact of atmospheric carbon on productivity, and C(t) and C' = 590 GtC represent present and preindustrial atmospheric gross carbon content, respectively. 

FeliX equation for net primary productivity NPP(t) [PgC/year], an expression of the annual biospheric uptake of atmospheric carbon. NPP' represents initial (ca. 1900) net primary productivity and is equal to 85.2 PgC/year. A dimensionless biostimulation coefficient ε = 0.35, describes the impact of atmospheric carbon on productivity, and C(t) and C' = 590 GtC represent present and preindustrial atmospheric gross carbon content, respectively. 

In the BAU scenario, the above equation evaluates to a gross uptake of roughly 90 PgC in 2010. This estimate is consistent with leading comprehensive assessments of global terrestrial NPP [1,2].

The biosphere also represents a source of carbon emissions. Annually, some 97% of the gross uptake of carbon is returned after a characteristic residence time (T = 10.6 years) to the atmosphere either directly or through an intermediate humus stage (T = 27.8 years).

As a result, terrestrial biomes represented a net sink of magnitude 2.2 PgC per year in 2010. This figure is in line with recent estimates, and is attributed almost entirely to forest productivity [2]. 

Emissions from land use and land use change are calculated separately, and range from 1.0-1.5 PgC per year, or 10% of total emissions in the BAU scenario.

[1] Haberl, H., et al.: Quantifying and mapping the human appropriation of net primary production in earth’s terrestrial ecosystems, vol. 104, pp. 12942–12945 (2007) 

[2] Pan, Y., et al.: A large and persistent carbon sink in the world’s forests. Science 333, 988–993 (2011)