Working Group III: Mitigation

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3.9 Summary and Conclusions

The analysis in this chapter is based upon a review of existing and emerging technologies, and the technological and economic potential that they have for reducing GHG emissions. In many areas, technical progress relevant to GHG emission reduction since the SAR has been significant and faster than anticipated. A broad array of technological options have the combined potential to reduce annual global greenhouse gas emission levels close to or below those of 2000 by 2010 and even lower by 2020.

Estimates of the technical potential, an assessment of the range of potential costs per metric tonne of carbon equivalent (tCeq), and the probability that a technology will be adopted are presented in Table 3.36 by sector. Specific examples and the estimation methodologies are discussed more fully in the chapter for each sector.

Table 3.36: Estimations of greenhouse gas emission reductions and cost per tonne of carbon equivalent avoided following the anticipated socio-economic potential uptake by 2010 and 2020 of selected energy efficiency and supply technologies, either globally or by region and with varying degrees of uncertainty
    US$/ tC avoided 2010 2020 References, comments, and relevant section in Chapter 3 of this report
Potentiala Probabilityb Potentiala Probabilityb
Residential sector OECD/ EIT Acosta Moreno et al., 1996;
Brown et al., 1998
Dev. cos. Wang and Smith, 1999
Commercial sector OECD/ EIT  
Dev. cos.  
Automobile efficiency improvements USA Interlab. Working Group, 1997
Brown et al., 1998
Europe US DOE/ EIA, 1998
ECMT, 1997 (8 countries only)
Japan Kashiwagi et al., 1999
Denis and Koopman, 1998
  Dev. cos. Worrell et al., 1997b
CO2 removal – fertilizer; refineries Global Table 3.21
Material efficiency improvement Global Table 3.21
Blended cements Global Table 3.21
N2O reduction by chem. indus. Global Table 3.21
PFC reduction by Al industry Global Table 3.21
HFC-23 reduction by chem. industry Global Table 3.21
Energy efficient improvements Global Table 3.19
Increased uptake of conservation tillage and cropland management Dev. cos. Zhou, 1998; Table 3.27
Dick et al ., 1998
Global IPCC, 2000
Soil carbon sequestration Global Lal and Bruce, 1999
Table 3.27
Nitrogenous fertilizer management OECD Kroeze & Mosier, 1999
Table 3.27
Global OECD, 1999; IPCC, 2000
Enteric methane reduction OECD Kroeze & Mosier, 1999
Table 3.27
USA OECD, 1998
Reimer & Freund, 1999
Dev. cos. Chipato, 1999
Rice paddy irrigation and fertilizers Global Riemer & Freund, 1999
IPCC, 2000
Landfill methane capture OECD Landfill methane USEPA, 1999
Energy supply              
Nuclear for coal Global   Totalsc – See Section 3.8.6
Annex I Table 3.35a
Non- Annex I Table 3.35b
Nuclear for gas Annex I Table 3.35c
Non- Annex I Table 3.35d
Gas for coal Annex I Table 3.35a
Non- Annex I Tables 3.35b
CO2 capture from coal Global Tables 3.35a + b
CO2 capture from gas Global Tables 3.35c + d
Biomass for coal Global Tables 3.35a + b
Moore, 1998; Interlab w. gp. 1997
Biomass for gas Global Tables 3.35c + d
Wind for coal or gas Global Tables 3.35a - d
BTM Cons 1999; Greenpeace, 1999
Co-fire coal with 10% biomass USA Sulilatu, 1998
Solar for coal Annex I Table 3.35a
Non- Annex I Table 3.35b
Hydro for coal Global Tables 3.35a + b
Hydro for gas Global Tables 3.35c + d

a Potential in terms of tonnes of carbon equivalent avoided for the cost range of US$/ tC given.
= <20 MtC/ yr      = 20- 50 MtC/ yr      = 50- 100MtC/ yr      = 100- 200MtC/ yr      = >200 MtC/ yr

b Probability of realizing this level of potential based on the costs as indicated from the literature.
= Very unlikely      = Unlikely      = Possible      = Probable      = Highly probable

c Energy supply total mitigation options assumes that not all the potential will be realized for various reasons including competition between the individual technologies as listed below the totals.

Available estimates of the technological potential to reduce greenhouse gas emissions and its costs suffer from several important limitations:

  • There are no consistent estimates of technological and economic potential covering all the major regions of the world;
  • Country- and region-specific studies employ different assumptions about the future progress of technologies and other key factors;
  • Studies make different assumptions about the difficulty of overcoming barriers to the market penetration of advanced technologies and the willingness of consumers to accept low-carbon technologies;
  • Most studies do not describe a range of costs over a domain of carbon reduction levels, and many report average rather than marginal mitigation costs; and
  • Social discount rates of 5%-12% are commonly used in studies of the economic potential for specific technologies which are lower than those typically used by individuals and in industry.

A summary of the estimates of the potential for worldwide emission reductions is given in Table 3.37. Overall, the total potential for worldwide greenhouse gas emissions reductions resulting from technological developments and their adoption are estimated to amount to 1,900-2,600MtC/yr by 201028 and 3,600–5,050MtC/yr by 2020.

Table 3.37: Estimates of potential global greenhouse gas emission reductions in 2010 and in 2020.
Historic emissions
in 1990
Historic Ceq annual
growth rate in
1990-1995 (%)
Potential emission
reductions in 2010
Potential emission
reductions in 2020
Net direct costs per tonne of carbon avoided
CO2 only
Most reductions are available at negative net direct costs.
CO2 only
Most studies indicate net direct costs less than US$25/tC
but two suggest net direct costs will exceed US$50/tC.
-energy efficiency
-material efficiency
CO2 only


More than half available at net negative direct costs.
Costs are uncertain.
Non-CO2 gases
N2O emissions reduction costs are US$0-$10/tCeq.
CO2 only
Non-CO2 gases
Most reductions will cost between US$0-100/tCeq with
limited opportunities for negative net direct cost options.
CH4 only
About 75% of the savings as methane recovery from
landfills at net negative direct cost; 25% at a cost of
Montreal Protocol
replacement applications
Non-CO2 gases
About half of reductions due to difference in study
baseline and SRES baseline values. Remaining half of
the reductions available at net direct costs below
Energy supply and
CO2 only (1620) 1.5 50-150 350-700 Limited net negative direct cost options exist; many
options are available for less than US$100/tCeq.
Total   6,900-8,400d   1,900-2,600e 3,600-5,050e  
a Buildings include appliances, buildings, and the building shell.
b The range for agriculture is mainly caused by large uncertainties about CH4, N2O, and soil-related emissions of CO2. Waste is dominated by landfill methane and the other sectors could be estimated with more precision as they are dominated by fossil CO2.
c Included in sector values above. Reductions include electricity generation options only (fuel switching to gas/nuclear, CO2 capture and storage, improved power station efficiencies, and renewables).
d Total includes all sectors reviewed in Chapter 3 for all six gases. It excludes non-energy related sources of CO2 (cement production, 160MtC; gas flaring, 60MtC; and land use change, 600-1,400MtC) and energy used for conversion of fuels in the end-use sector totals (630MtC). Note that forestry emissions and their carbon sink mitigation options are not included.
e The baseline SRES scenarios (for six gases included in the Kyoto Protocol) project a range of emissions of 11,500-14,000MtCeq for 2010 and of 12,000-16,000MtCeq for 2020. The emissions reduction estimates are most compatible with baseline emissions trends in the SRES-B2 scenario. The potential reductions take into account regular turnover of capital stock. They are not limited to cost-effective options, but exclude options with costs above US$100/tCeq (except for Montreal Protocol gases) or options that will not be adopted through the use of generally accepted policies.

In the scenarios that were constructed within the SRES emissions of the six Kyoto Protocol greenhouse gases develop as follows (in MtCeq, rounded numbers):

   1990: 9,500
   2000: 10,500
   2010: 11,500 – 13,800
   2020: 12,000 – 15,900

It was not possible to calculate the emission reduction potential of the short-term mitigation options presented in this Chapter on the basis of the SRES scenarios, mainly because of lack of technological detail in the SRES. In order to come to a comprehensive emission reduction estimate, it has been ensured that for all the sectors the estimates are compatible with one of the scenarios, i.e. the B2-Message (standardized) scenario. The emission reductions presented in Table 3.37 total 14% - 23% of baseline emissions in the year 2010 and to 23% - 42% of baseline emissions in the year 2020.29 If these percentages also apply to the other scenarios - there is no obvious reason why this would not be the case – it is concluded that in most situations the annual global greenhouse gas emission levels can be reduced to a level close to or below those of 2000 by 2010 and even lower by 2020.

The evidence on which this conclusion is based is extensive, but is subject to the limitations outlined above. Therefore, the estimates as presented in the table should be considered to be indicative only. Nevertheless, the main conclusion presented above can be drawn with a high degree of confidence.

Costs of options vary by technology, sector and region (see cost discussion in Table 3.37). Based upon the costs in a majority of the studies, approximately half of the potential for emissions reductions cited above for 2010 and 2020 can be achieved at net negative costs (value of energy saved exceeds capital, operating and maintenance costs) using the social discount rates cited. Most of the remainder can be achieved at a cost of less than US$100/tCeq.

The overall rate of diffusion of low emission technologies is insufficient to offset the societal trend of increasing consumption of energy-intensive goods and services, which results in increased emissions. Nevertheless, substantial technical progress has been made in many areas, including the market introduction of efficient hybrid engine cars, the demonstration of underground carbon dioxide storage, the rapid advancement of wind turbine design, and the near elimination of N2O emissions from adipic acid production.

Hundreds of technologies and practices exist to reduce greenhouse gas emissions from the buildings, transport, and industrial sectors. These energy efficiency options are responsible for more than half of the total emission reduction potential of these sectors. Efficiency improvements in material use (including recycling) will also become more important in the longer term.

The energy supply and conversion sector will remain dominated by cheap and abundant fossil fuels but with potential for reduction in emission caused by the shift from coal to natural gas, conversion efficiency improvement of power plants, the adoption of distributedcogeneration plants, and carbon dioxide recovery and sequestration. The continued use of nuclear power plants (including their lifetime extension) and the application of renewable energy sources will avoid emissions from fossil fuel use. Biomass from by-products, wastes, and methane from landfills is a potentially important energy source which can be supplemented by energy crop production where suitable land and water are available. Wind energy and hydropower will also contribute, more so than solar energy because of the latter’s relatively high costs.

N2O and some fluorinated greenhouse gas reductions have already been achieved through major technological advances. Process changes, improved containment, recovery and recycling, and the use of alternative compounds and technologies have been implemented. Potential for future reductions exists, including process-related emissions from insulated foam and semiconductor production, and by-product emissions from aluminium and HCFC-22. The potential for energy efficiency improvements connected to the use of fluorinated gases is of a similar magnitude to reductions of direct emissions.

Agriculture contributes 20% of total global anthropogenic emissions, but although there are a number of technology mitigation options available, such as soil carbon sequestration, enteric methane control, and conservation tillage, the widely diverse nature of the sector makes capture of emission reductions difficult.

Appropriate policies are required to realize these potentials. Furthermore, on-going research and development is expected to significantly widen the portfolio of technologies to provide emission reduction options. Maintaining these R&D activities together with technology transfer actions will be necessary if the longer term potential as outlined in Table 3.37 is to be realized. Balancing mitigation activities in the various sectors with other goals such as those related to development, equity, and sustainability is the key to ensuring they are effective.

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