Saturation of the Terrestrial Carbon Sink

Abstract

There is strong evidence that the terrestrial biosphere has acted as a net carbon (C) sink over the last two and half decades. Its strength is highly variable year-to-year ranging from 0.3 to 5.0 Pg C yr1; an amount of signifi- cant magnitude compared to the emission of about 7 Pg C yr1 from fossil fuel burning (Prentice et al. 2001; Schimel et al. 2001; Sabine et al. 2004). Uncertainties as- sociated with C emissions from land-use change are large. On average, the terrestrial C sink is responsible for re- moving from the atmosphere approximately one third of the CO2 emitted from fossil fuel combustion, thereby slowing the build-up of atmospheric CO2. The ocean sink is of similar magnitude (Sabine et al. 2004). Given the international efforts to stabilize atmospheric CO2 con- centration and climate (i.e., Kyoto Protocol, C trading markets), the terrestrial C sink can be viewed as a sub- sidy to our global economy worth trillions of dollars. Because many aspects of the terrestrial C sink are ame- nable to purposeful management, its basis and dynam- ics need to be well understood.