Probably the single greatest motivation for adopting a new technology is direct cost: If it is cheaper than existing technologies it is adopted quickly. Externalities rarely figure into private sector motivations unless encouraged with government incentives or regulatory structures. Nevertheless, a number of mitigation options have ancillary benefits that can substantially multiply their value to GHG mitigation per se.
Biosphere sequestration of carbon and mitigation of non-CO2 fluxes are two areas that can have substantial societal value beyond GHG mitigation. Organic carbon sequestered in soil contributes to soil and hence ecosystem health, with benefits for soil and water conservation, nutrient storage, porosity, invertebrate biodiversity, plant health, and ground and surface water quality. Carbon sequestered in reestablished and regrowing forests has similar benefits for forested watersheds, in addition to abetting plant and animal biodiversity. Thus, organic carbon storage has important practical implications for drinking water quality, coastal fisheries, farmland quality, and flood protection.
Reducing the emission of non-CO2 greenhouse gases also provides ancillary benefits. N2O suppression through the better management of nitrogen in cropping systems will help to keep exogenous nitrogen from environmental fates other than crop yields (e.g., air pollution). At present the amount of nitrogen fixed by anthropogenic means is close to that fixed biologically; because less than half of the fertilizer applied to cropping systems is taken up by the crop and the remainder is available to cause significant environmental harm. Likewise CH4 capture from waste handling can provide energy savings for individual farms and perhaps rural communities, and composted waste applied to soils can substitute for synthetic fertilizer, with its economic and CO2 manufacturing cost.
Additionally, industrial capture of carbon and higher carbon use efficiency in the industrial and transport sectors will lead to the emission of fewer industrial non-CO2 greenhouse gases. Black carbon, while not a gas, is nonetheless responsible for about 7 percent of the radiative forcing attributable to anthropogenic sources, and cleaner power generation will reduce radiative forcings from this source. Likewise, lower emissions of the ozone precursors—namely NOx, CO, and the non-methane volatile organic carbons (NMVOCs)—will potentially reduce concentrations of tropospheric ozone, responsible for about 12 percent of total anthropogenic radiative forcing (see Prinn, Chapter 9, and Robertson, Chapter 29). NOx reductions will attenuate both rainfall acidity and much of the unintentional nitrogen deposition now occurring over much of the Earth's surface (Holland et al. 1999).
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