The greenhouse gas mitigation potential of different economic sectors in three world regions are estimated using a bottom-up approach. These estimates provide updates of the numbers reported in the Fourth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC AR4). This study is part of a larger project aimed at comparing greenhouse gas mitigation potentials from bottom-up and top-down approaches. The sectors included in the analysis are energy supply, transport, industry and the residential and service sector. The mitigation potentials range from 11 to 15GtCO₂eq. This is 26-38% of the baseline in 2030 and 47-68% relative to the year 2000. Potential savings are estimated for different cost levels. The total potential at negative costs is estimated at 5-8% relative to the baseline, with the largest share in the residential and service sector and the highest reduction percentage for the transport and industry sectors. These (negative) costs include investment, operation and maintenance and fuel costs and revenues at moderate discount rates of 3-10%. At costs below 100US$/tCO₂, the largest potential reductions in absolute terms are estimated in the energy supply sector, while the transport sector has the lowest reduction potential.

The Fourth Assessment Report of IPCC reports that greenhouse gas emissions can be reduced by about 30-50% in 2030 at costs below 100 US$/tCO₂ based on an assessment of both bottom-up and top-down studies. Here, we have looked in more detail into the outcomes of specific models and also analyzed the economic potentials at the sectoral and regional level. At the aggregated level, the findings of the IPCC report are confirmed. However, substantial differences are found at the sectoral level. At the same time, there seems to be no systematic difference in the reduction potential reported by top-down and bottom-up approaches. The largest reduction potential as a response to carbon prices exists in the energy supply sector. Reduction potential in the building sector may carry relatively low costs. Although uncertainties are considerable, the modeling results and the bottom-up analyses all suggest that at the global level around 50% of greenhouse gas emissions may be reduced at carbon price (costs) below 100$/tCO₂-eq-but with a wide range of 30-60%. At a carbon price (costs) less than 20$/tCO₂-eq, still 10-35% of emissions may be abated. The variation of results is higher at low carbon-price levels than at high levels.