Carbon emissions from land use and land-cover change

[摘要] The net flux of carbon from land use and land-cover change (LULCC) accountedfor 12.5% of anthropogenic carbon emissions from 1990 to 2010. This netflux is the most uncertain term in the global carbon budget, not only becauseof uncertainties in rates of deforestation and forestation, but also becauseof uncertainties in the carbon density of the lands actually undergoingchange. Furthermore, there are differences in approaches used to determinethe flux that introduce variability into estimates in ways that are difficultto evaluate, and not all analyses consider the same types of managementactivities. Thirteen recent estimates of net carbon emissions from LULCC aresummarized here. In addition to deforestation, all analyses consideredchanges in the area of agricultural lands (croplands and pastures). Someconsidered, also, forest management (wood harvest, shifting cultivation).None included emissions from the degradation of tropical peatlands. Means andstandard deviations across the thirteen model estimates of annual emissionsfor the 1980s and 1990s, respectively, are 1.14 ± 0.23 and1.12 ± 0.25 Pg C yr⁻¹ (1 Pg = 10¹⁵ g carbon). Fourstudies also considered the period 2000–2009, and the mean and standarddeviations across these four for the three decades are 1.14 ± 0.39,1.17 ± 0.32, and 1.10 ± 0.11 Pg C yr⁻¹. For the period1990–2009 the mean global emissions from LULCC are1.14 ± 0.18 Pg C yr⁻¹. The standard deviations across modelmeans shown here are smaller than previous estimates of uncertainty as theydo not account for the errors that result from data uncertainty and from anincomplete understanding of all the processes affecting the net flux ofcarbon from LULCC. Although these errors have not been systematicallyevaluated, based on partial analyses available in the literature and expertopinion, they are estimated to be on the orderof ± 0.5 Pg C yr⁻¹.

[学科分类] 地球化学与岩石