What would constitute a suitable level of carbon storage in natural habitats remains an open question. If we arbitrarily assume we need to protect 75–90% of the unprotected carbon stock, this would require protection of an additional 7–14% of land area if the areas with the highest carbon density were selected. Although these are crude estimates they nevertheless illustrate the magnitude of the additional area required to attain an ambitious target of carbon storage in natural terrestrial habitats. The conversion of unprotected ecosystems with high carbon storage would exacerbate CO2 emissions, and therefore efforts to mitigate climate change would need to ensure higher carbon storage. For example, adding the extra 14.3% of land required to reach the target of storing 90% of biomass carbon in natural habitats would secure c. 246 Pg C. In comparison, CO2 emissions from fossil fuel in 2009 constituted 30.8 Pg CO2 (the equivalent of 8.4 ± SE 0.5 Pg C; Friedlingstein et al., 2010). If all the carbon stored in the extra c. 14.3% of important areas for carbon were emitted as a result of land-use change, the resulting CO2 emissions would be c. 29 times the global fossil fuel CO2 emissions in 2009 (246/8.4529). We focused on living biomass carbon (and omitted soil organic carbon and dead biomass carbon) as there is much more uncertainty in the change of these carbon pools following land-use change. In general a smaller portion of soil carbon and dead biomass carbon is emitted following land-use change such as deforestation (Brown, 2002), but degradation of peat can release considerable amounts of CO2 (van der Werf et al., 2009). Although other data and methods may reveal other important areas for carbon storage, the magnitude of the extra area needed to reach high targets for carbon storage seems less likely to change.
What would constitute a suitable level of carbon storage in natural habitats remains an open question. If we arbitrarily assume we need to protect 75–90% of the unprotected carbon stock, this would require protection of an additional 7–14% of land area if the areas with the highest carbon density were selected. Although these are crude estimates they nevertheless illustrate the magnitude of the additional area required to attain an ambitious target of carbon storage in natural terrestrial habitats. The conversion of unprotected ecosystems with high carbon storage would exacerbate CO2 emissions, and therefore efforts to mitigate climate change would need to ensure higher carbon storage. For example, adding the extra 14.3% of land required to reach the target of storing 90% of biomass carbon in natural habitats would secure c. 246 Pg C. In comparison, CO2 emissions from fossil fuel in 2009 constituted 30.8 Pg CO2 (the equivalent of 8.4 ± SE 0.5 Pg C; Friedlingstein et al., 2010). If all the carbon stored in the extra c. 14.3% of important areas for carbon were emitted as a result of land-use change, the resulting CO2 emissions would be c. 29 times the global fossil fuel CO2 emissions in 2009 (246/8.4529). We focused on living biomass carbon (and omitted soil organic carbon and dead biomass carbon) as there is much more uncertainty in the change of these carbon pools following land-use change. In general a smaller portion of soil carbon and dead biomass carbon is emitted following land-use change such as deforestation (Brown, 2002), but degradation of peat can release considerable amounts of CO2 (van der Werf et al., 2009). Although other data and methods may reveal other important areas for carbon storage, the magnitude of the extra area needed to reach high targets for carbon storage seems less likely to change.
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