EXECUTIVE SUMMARY Mitigation potentials and costs from sectoral studies The economic potentials for GHG mitigation at different costs have been reviewed for 2030 on the basis of bottom-up studies. The review confirms the Third Assessment Report (TAR) finding that there are substantial opportunities for mitigation levels of about 6 GtCO 2 -eq involving net benefits (costs less than 0), with a large share being located in the buildings sector. Additional potentials are 7 GtCO 2 -eq at a unit cost (carbon price) of less than 20 US$/tCO 2 -eq, with the total, low-cost, potential being in the range of 9 to 18 GtCO 2 -eq. The total range is estimated to be 13 to 26 GtCO 2 -eq, at a cost of less than 50 US$/tCO 2 -eq and 16 to 31 GtCO 2 -eq at a cost of less than 100 US$/tCO 2 -eq (370 US$/tC-eq). As reported in Chapter 3, these ranges are comparable with those suggested by the top-down models for these carbon prices by 2030, although there are differences in sectoral attribution ( medium agreement, medium evidence ). No one sector or technology can address the entire mitigation challenge. This suggests that a diversified portfolio is required based on a variety of criteria. All the main sectors contribute to the total. In the lower-cost range, and measured according to end-use attribution, the potentials for electricity savings are largest in buildings and agriculture. When attribution is based on point of emission, energy supply makes the largest contribution ( high agreement, much evidence ).
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