Wetlands global extent

Table 1.1 Global extent of wetlands of different types...

Figure 6.1. Ecosystem area and soil carbon content to 3-m depth. Lower Panel Global areal extent of major ecosystems, transformed by land use in yellow, untransformed in purple. Data from Hassan et al. (2005) except for Mediterranean-climate ecosystems transformation impact is from Myers et al. (2000) and ocean surface area is from Hassan et al. (2005). Upper Panel Total C stores in plant biomass, soil, yedoma/permafrost. D, deserts G S(tr), tropical grasslands and savannas G(te), temperate grasslands ME, Mediterranean ecosystems F(tr), tropical forests F(te), temperate forests F(b), boreal forests T, tundra FW, freshwater lakes and wetlands C, croplands O, oceans. Data are from Sabine et al. (2004), except C content of yedoma permafrost and permafrost (hght blue columns, left and right, respectively Zimov et al., 2006), and ocean organic C content (dissolved plus particulate organic Denman et al., 2007). This figure considers soil C to 3-m depth (Jobbagy and Jackson, 2000). Approximate carbon content of the atmosphere is indicated by the dotted lines for last glacial maximum (LGM), pre-industrial (P-IND) and current (about 2000). Reprinted from Fischlin et al. (2007) in IPCC (2007). See color insert.

As a result of these uncertainties, the acmal contribution of wetlands to the atmospheric methane budget is even more poorly known than the factor-of-two that is usually quoted (Cicerone and Oremland, 1988). Another important consideration is that the areal extent of various types of wetlands worldwide is only known to a factor of two (Aselmann and Crutzen, 1989 Fung et al, 1991 Chapman, 1977). Bartlett et al. (1989) have discussed the large variations of methane fluxes measured from adjacent but diverse wetlands (Everglades) and the related problems of estimating a global wetland flux. Thus, the uncertainty in methane emissions from wetlands may vary by a factor of two or three. 

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