IPCC Fourth Assessment Report: Climate Change 2007
Climate Change 2007: Working Group III: Mitigation of Climate Change

Regional modelling assessments

Bottom-up regional studies show that forestry mitigation options have the economic potential (at costs up to 100 US$/tCO2-eq) to contribute 1.3-4.2 MtCO2/yr Errata (average 2.7 GtCO2/yr) in 2030 excluding bioenergy. About 50% can be achieved at a cost under 20 US$/tCO2 (1.6 GtCO2/yr) with large differences between regions. The combined effects of reduced deforestation and degradation, afforestation, forest management, agro-forestry and bioenergy have the potential to increase from the present to 2030 and beyond. This analysis assumes gradual implementation of mitigation activities starting now (medium agreement, medium evidence) [9.4.4].

Global top-down models predict mitigation potentials of 13.8 GtCO2-eq/yr in 2030 at carbon prices less than or equal to 100 US$/tCO2. The sum of regional predictions is 22% of this value for the same year. Regional studies tend to use more detailed data and consider a wider range of mitigation options, and thus may more accurately reflect regional circumstances and constraints than simpler, more aggregated global models. However, regional studies vary in model structure, coverage, analytical approach and assumptions (including baseline assumptions). Further research is required to narrow the gap in the estimates of mitigation potential from global and regional assessments (medium agreement, medium evidence) [9.4.3].

The best estimate of the economic mitigation potential for the forestry sector at this stage therefore cannot be more certain than a range between 2.7 and 13.8 GtCO2/yr in 2030, for costs <100 US$/tCO2; for costs <20 US$/tCO2 the range is 1.6 to 5 GtCO2/yr. About 65% of the total mitigation potential (up to 100 US$/tCO2-eq) is located in the tropics and about 50% of the total could be achieved by reducing emissions from deforestation (low agreement, medium evidence).

Forestry can also contribute to the provision of bioenergy from forest residues. The potential of bioenergy, however, is counted in the power supply, transportation (biofuels), industry and building sectors (see Chapter 11 for an overview). Based on bottom-up studies of potential biomass supply from forestry, and assuming that all of that will be used (which depends entirely on the cost of forestry biomass compared with other sources) a contribution in the order of 0.4 GtCO2/yr could come from forestry.

Global top-down models are starting to provide insight on where and which of the carbon mitigation options can best be allocated on the globe (Figure TS.24).

Figure TS.24Figure TS.24

Figure TS.24: Allocation of global afforestation activities as given by two global top-down models. Top: location of bioenergy and carbon plantations in the world in 2100; bottom: percentage of a grid cell afforested in 2100 [Figure 9.11].