IPCC Fourth Assessment Report: Climate Change 2007
Climate Change 2007: Working Group III: Mitigation of Climate Change Estimates of mitigation potentials from Chapters 4 to 10

Table 11.3 uses the procedures outlined above to bring together the estimates for the economic potentials for GHG mitigation from Chapters 4 to 10. It was not possible to break down the potential into the desired cost categories for all sectors. Where appropriate, then, the cells in the table have been merged to account for the fact that the numbers represent the total of two cost categories. Only the potentials in the cost categories up to 100 US$/tCO2-eq are reported here. Some of the chapters also report numbers for the potential in higher cost categories. This is the case for Chapter 5 (transport) and Chapter 8 (agriculture).

Table 11.3 suggests that the economic potential for reducing GHG emissions at costs below 100 US$/tCO2 ranges[7] from 16 to 30 GtCO2-eq. The contributions of each sector to the totals are in the order of magnitude 2 to 6 GtCO2-eq (mid-range numbers), except for the waste sector (0.4 to 1 GtCO2-eq). The mitigation potentials at the lowest cost are estimated for the buildings sector. Based on the literature assessment presented in Chapter 6 it can be concluded that over 80% of the buildings potential can be identified at negative cost. However, significant barriers need to be overcome to achieve these potentials. See Chapter 6 for more information on these barriers.

In all sectors, except for the transport sector, the highest economic potential for emission reduction is thought to be in the non-OECD/EIT region. In relative terms, although it is not possible to be exact because baselines across sectors are different, the emission reduction options at costs below 100 US$/tCO2-eq are in the range of 30 to 50% of the totalled baseline. This is an indicative figure as it is compiled from a range of different baselines.

Table 11.3: Estimated economic potentials for GHG mitigation at a sectoral level in 2030 for different cost categories using the SRES B2 and IEA World Energy Outlook (2004) baselines

Sector Mitigation optiona) Region Economic potential <100 US$/tCO2-eqc) Economic potential in different cost categoriesd), e) 
Cost cat. US$/tCO2-eq <0 0-20 20-50 50-100 
Cost cat. US$/tC-eq <0 0-73 73-183 183-367 
Low High         
Gt CO2-eq 

Energy supplye)

(see also 4.4)

All options in energy supply excl. electricity savings in other sectors OECD 0.90 1.7 0.9   0.50 
EIT 0.20 0.25 0.15   0.06 
Non-OECD/EIT 1.3 2.7 0.80   0.90 0.35 
Global 2.4 4.7 1.9   1.4 0.35 

Transportb), e), g)

(see also 5.6)

Total OECD 0.50 0.55 0.25 0.25 
EIT 0.05 0.05 0.03 0.02 
Non-OECD/EIT 0.15 0.15 0.10 0.03 0.02 
Globalb) 1.6 2.5 0.35 1.4 0.15 0.15 


(see also 6.4)f), h)

Electricity savings OECD 0.8 1.0 0.95 0.00   
EIT 0.2 0.3 0.25   
Non-OECD/EIT 2.0 2.5 2.1 0.05 0.05   
Fuel savings OECD 1.0 1.3 0.85 0.15 0.15   
EIT 0.6 0.8 0.2 0.15 0.35   
Non-OECD/EIT 0.7 0.8 0.65 0.10 0.01   
Total OECD 1.8 2.3 1.8 0.15 0.15   
EIT 0.9 1.1 0.45 0.15 0.35   
Non-OECD/EIT 2.7 3.3 2.7 0.15 0.10   
Global 5.4 6.7 5.0 0.50 0.60   


(see also 7.5)

Electricity savings OECD 0.30   0.07   0.07 0.15 
EIT 0.08   0.02   0.02 0.040 
Non-OECD/EIT 0.45   0.10   0.10 0.25 
Other savings, including non-CO2 GHG OECD 0.35 0.90 0.30   0.25 0.05 
EIT 0.20 0.45 0.08   0.25 0.02 
Non-OECD/EIT 1.2 3.3 0.50   1.7 0.08 
Total OECD 0.60 1.2 0.35   0.35 0.20 
EIT 0.25 0.55 0.10   0.25 0.06 
Non-OECD/EIT 1.6 3.8 0.60   1.8 0.30 
Global 2.5 5.5 1.1   2.4 0.55 


(see also 8.4)

All options OECD 0.45 1.3 0.30   0.20 0.30 
EIT 0.25 0.65 0.15   0.10 0.15 
Non-OECD/EIT 1.6 4.5 1.1   0.75 1.2 
Global 2.3 6.4 1.6   1.1 1.7 


(see also 9.4)

All options OECD 0.40 1.0 0.01 0.25 0.30 0.25 
EIT 0.09 0.20 0.05 0.05 0.05 
Non-OECD/EIT 0.75 3.0 0.15 0.90 0.55 0.35 
Global 1.3 4.2 0.15 1.1 0.90 0.65 


(see also 10.4)

All options OECD 0.10 0.20 0.10 0.06 0.00 0.00 
EIT 0.10 0.10 0.05 0.05 0.00 0.00 
Non-OECD/EIT 0.20 0.70 0.25 0.07 0.10 0.04 
Global 0.40 1.0 0.40 0.18 0.10 0.04 

All sectorsi)

All options OECD 4.9 7.4 2.2 2.1 1.3 1.1 
EIT 1.8 2.8 0.55 0.65 0.50 1.0 
Non-OECD/EIT 8.3 16.8 3.3 3.6 4.1 2.4 
Global 15.8 31.1 6.1 7.4 6.0 4.5 


a) Several reduction options are not included due to limited literature sources. This underestimation could be about 10–15%; see below.

b) For transport, the regional data by cost category do not add up to the global potential: regional (cost) distribution is available for LDV only. Due to the lack of international agreement about the regional allocation of aviation emissions, only global cost distributions are available for aviation. A lack of data means that only global figures are presented for biofuels, and not cost distribution.

c) The ranges indicated by the potential are derived differently for each chapter. See underlying chapters for more information.

d) The economic potential figures per cost category are mid-range numbers.

e) The mitigation potential for the use of biomass is allocated to the transport and power sector. See the discussion on biomass energy in

f) For the buildings sector the literature mainly focuses on low-cost mitigation options, and the potential in high-cost categories may be underestimated. The zero may represent an underestimation of the emissions.

g) The ‘0’ means zero, 0.00 means a value below 5 Mton.

h) The electricity savings in the end-use sectors Buildings and Industry are the high estimates. The electricity savings would be significantly lower if the order of measurement were to be reversed; the substitution potential in the energy sector would have been assessed before electricity savings (see Appendix 11.1).

i) The tourism sector is included in the buildings and the transport sector.

A number of comments should be made on the overview presented in Table 11.3.

First, a set of emission reduction options have been excluded from the analysis, because the available literature did not allow for a reliable assessment of the potential.[8]

  • Emission reduction estimates of fluorinated gases from energy supply, transport and buildings are not included in the sector mitigation potentials from Chapters 4 to 6. For these sectors, the special IPCC report on ozone and climate (IPCC & TEAP, 2005) reported a mitigation potential for HFCs of 0.44 GtCO2-eq for the year 2015 (a mitigation potential of 0.46 GtCO2-eq was reported for CFCs and HCFCs).
  • The potential for combined generation of heat and power in the energy supply sector has not added to the other potentials as it is uncertain (see Section 4.4.3). IEA (2006a) quotes a potential here of 0.2 to 0.4 GtCO2-eq.
  • The potential emissions reduction for coal mining and gas pipelines has not been included in the reductions from the power sector. De Jager et al. (2001) indicated that the CH4 emissions from coal mining in 2020 might be in the order of 0.65 GtCO2-eq. Reductions of 70 to 90% with a penetration level of 40% might be possible, resulting for 2020 in the order of 0.20 GtCO2-eq. Higher reduction potentials of 0.47 GtCO2-eq for CH4 from coal mining have also been mentioned (Delhotal et al., 2006).
  • Emission reductions in freight transport (heavy duty vehicles), public transport, and marine transport have not been included. In the transport sector, only the mitigation potential for light duty vehicle efficiency improvement (LDV), air planes and biofuels for road transport has been assessed. Because LDV represents roughly two-thirds of transportation by road, and because road transportation represents roughly three-quarters of transport as a whole (air, water, and rail transport represent roughly 11, 9 and 3 percent of overall transport respectively), the estimate for LDV broadly reflects half of the transport activity for which a mitigation potential of over 0.70 GtCO2-eq is reported. In the case of marine transport, the literature studies discussed in Section 5.3.4 indicate that large reductions are possible compared to the current standard but this might not be significant when comparing to a baseline. See also Table 5.8 for indicative potentials for some of the options.
  • Non-technical options in the transport sector, like speed limits and changes in modal split or behaviour changes, are not taken into account (an indication of the order of magnitude for Latin American cities is given in Table 5.6).
  • For the buildings sector, most literature sources focused on low-cost mitigation options and so high-cost options are less well represented. Behavioural changes in the buildings sector have not been included; some of these raise energy demand, examples being rebound effects from improvements in energy efficiency.[9]
  • In the industry sector, the fuel savings have only been estimated for the energy-intensive sectors representing approximately 50% of fuel use in manufacturing industry.
  • The TAR stated an emission reduction estimate of 2.20 GtCO2-eq in 2020 for material efficiency. Chapter 7 does not include material efficiency, except for recycling for selected industries, in the estimate of the industrial emission reduction potential. To avoid double counting, the TAR estimate should not be added to the potentials of Chapter 7. However, it is likely that the potential for material efficiency significantly exceeds that for recycling for selected industries only given in Chapter 7.

In conclusion, the options excluded represent significant potentials that justify future analysis. These options represent about 10 to 15% of the potential reported in Table 11.3; this magnitude is not such that the conclusions of the bottom-up analysis would change substantially.

Secondly, the chapters identified a number of key sensitivities that have not been quantified. Note that the key sensitivities are different for the different sectors.

In general, higher energy prices will have some impact on the mitigation potentials presented here (i.e. those with costs below 100 US$/tCO2-eq), but the impact is expected to be generally limited, except for the transport sector (see below). No major options have been identified exceeding 100 US$/tCO2-eq that could move to below 100 US$/tCO2-eq. However, this is only true of the fairly static approach presented here. The costs and potential of technologies in 2030 may be different if energy prices remain high for several decades compared to the situation if they return to the levels of the 1990s. High energy prices may also impact the baseline since the fuel mix will change and lower emissions can be expected. Note that options in some areas, such as agriculture and forestry and non-CO2 greenhouse gases (about one third of the potential reported), are not affected by energy prices, or much less so.

More specifically, an important sensitivity for the transport sector is the future oil price. The total potential for the LDV in transport increases by 7% as prices rise from 30 to 60 US$/barrel. However, the potential at costs <0 US$/tCO2 increases much more – by almost 90% – because of the fuel saving effect. (See Section 5.4.2).

  • Discount rates that formed the basis of the analysis are – as reported in the individual chapters – in the range of 3 to 10%, with the majority of studies using the lower end of this range. Lower discount rates (e.g. 2%) would imply some shift to lower cost ranges, without substantially affecting the total potential. Moving to higher discount rates would have a particular impact on the potential in the highest cost range, which makes up 15 to 20% of the total potential.
  • Agriculture and forestry potential estimates are based on long-term experimental results under current climate conditions. Given moderate deviations in the climate expected by 2030, the mitigation estimates are considered quite robust.

Thirdly, potentials with costs below zero US$/tCO2-eq are presented in Table 11.3. The potential at negative cost is considerable. There is evidence from business studies showing the existence of mitigation options at negative cost (for example, The Climate Group, 2005). For a discussion of the reasons for mitigation options at negative costs, see IPCC (2001), Chapters 3 and 7; and Chapters 2 and 6, and Section 11.6 of this report.

These remarks do not affect the validity of the overall findings, i.e. that the economic potential at costs below 100 US$/tCO2-eq ranges from 16 to 30 GtCO2-eq. However, they reflect a basic shortcoming of the bottom-up analysis. For individual countries, sectors or gases, the literature includes excellent bottom-up analysis of mitigation potentials. However, they are usually not comparable and their coverage of countries/sectors/gases is limited.

The following gaps in the literature have been identified. Firstly, there is no harmonized integrated standard for bottom-up analysis that compares all future economic potentials. Harmonization is considered important for, inter alia, target years, discount rates, price scenarios. Secondly, there is a lack of bottom-up estimates of mitigation potentials, including those for rebound effects of energy-efficiency policies for transport and buildings, for regions such as many EIT countries and substantial parts of the non-OECD/EIT grouping.

  1. ^  Note that the range is found by aggregating the low or the high potentials per sector. As the errors in the potentials by sector are not correlated, counting up the errors using error propagation rules would lead to a range about half this size. However, given all the uncertainties, and in order to make statements with enough confidence, the full range reported here is used.
  2. ^  As indicated in the notes to Table 11.1, bog fires in the forestry sector have also been excluded from the emissions and therefore from the reduction potential as well. The emissions may be significant (in the order of 3 GtCO2-eq), see Chapter 1.
  3. ^  Greening et al. (2000, p.399), in a survey of the rebound effect (in which efficiency improvements lead to more use of energy), remark that ‘rebound is not high enough to mitigate the importance of energy efficiency as a way of reducing carbon emissions. However, climate policies that rely only on energy efficiency technologies may need reinforcement by market instruments such as fuel taxes and other incentive mechanisms.’