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FIGURE 6.4 Radiative forcing of climate between 1750 and 2005 due to both human activities and natural processes, expressed in Watts per square meter (energy per unit area). Positive values correspond to warming. See text for details. SOURCE: Forster et al. (2007).

FIGURE 6.4 Radiative forcing of climate between 1750 and 2005 due to both human activities and natural processes, expressed in Watts per square meter (energy per unit area). Positive values correspond to warming. See text for details. SOURCE: Forster et al. (2007).

(Forster et al., 2007) (see Figure 6.4). Forcing estimates for all of the well-mixed GHGs are quite accurate because we have precise measurements of their concentrations, their influence on the transfer of radiation through the atmosphere is well understood, and they become relatively evenly distributed across the global atmosphere within a year or so of being emitted.


Methane (CH4). Methane is produced from a wide range of human activities, including natural gas management, fossil fuel and biomass burning, animal husbandry, rice cultivation, and waste management (Houweling et al., 2006). Natural sources of CH4—which are smaller than human sources—include wetlands and termites, and both of



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