Climate Change 2001:
Working Group III: Mitigation
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Figure 4.2: Different ecosystems, their components, and human activities. The carbon stocks associated with the different ecosystems are stored in aboveground and belowground biomass, detrital material (dead organic matter), and soils. Carbon is withdrawn from the atmosphere through photosynthesis (vertical down arrow), and returned by oxidation processes that include plant respiration, decomposition, and combustion (vertical up arrow). Carbon is also transferred within ecosystems and to other locations (horizontal arrows). Both natural processes and human activities affect carbon flows. Mitigation activities directed at one ecosystem component generally have additional effects influencing carbon accumulation in, or loss from, other components. Estimates of ecosystem and atmospheric C stocks are adapted from Bolin et al. (2000). Values for C stocks in some ecosystems are still very uncertain. Not shown are estimates of C stocks in tundra (127GtC), deserts and semi-deserts (199GtC), and oceans (approx. 39,000GtC) (numbers are taken from Special Report on LULUCF, Fig 1-1, page 30; IPCC, 2000a).

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