Climate Change 2001:
Other reports in this collection
Table SPM.1: Estimates of potential global greenhouse gas emission reductions in 2010 and in 2020 (Sections 3.3-3.8 and Chapter 3 Appendix)
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.
  CO2 only


  -energy efficiency      
More than half available at net negative direct costs.
 -material efficiency      
Costs are uncertain.
  Non-CO2 gases
N2O emissions reduction costs are US$0-US$10/tCeq.
Agricultureb           Most reductions will cost between US$0-100/tCeq with limited opportunities for negative net direct cost options.
  Non-CO2 gases  
  CH4 only




About 75% of the savings as methane recovery from landfills at net negative direct cost; 25% at a cost of US$20/tCeq.
  Non-CO2 gases




About half of reductions due to difference in study replacement applications baseline and SRES baseline values. Remaining half of the reductions available at net direct costs below US$200/tCeq.
Energy supply and conversionc           Limited net negative direct cost options exist; many options are available for less than US$100/tCeq.
  CO2 only  
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 turn-over 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.

9. . To achieve stabilization at these levels, the scenarios suggest that a very significant reduction in world carbon emissions per unit of GDP from 1990 levels will be necessary. Technological improvement and technology transfer play a critical role in the stabilization scenarios assessed in this report. For the crucial energy sector, almost all greenhouse gas mitigation and concentration stabilization scenarios are characterized by the introduction of efficient technologies for both energy use and supply, and of low- or no-carbon energy. However, no single technology option will provide all of the emissions reductions needed. Reduction options in non-energy sources and non-CO2 greenhouse gases will also provide significant potential for reducing emissions. Transfer of technologies between countries and regions will widen the choice of options at the regional level and economies of scale and learning will lower the costs of their adoption (Sections 2.3.2, 2.4, 2.5).

Box SPM.2. Approaches to Estimating Costs and Benefits, and their Uncertainties

For a variety of factors, significant differences and uncertainties surround specific quantitative estimates of the costs and benefits of mitigation options. The SAR described two categories of approaches to estimating costs and benefits: bottom-up approaches, which build up from assessments of specific technologies and sectors, such as those described in Paragraph 7, and top-down modelling studies, which proceed from macroeconomic relationships, such as those discussed in Paragraph 13. These two approaches lead to differences in the estimates of costs and benefits, which have been narrowed since the SAR. Even if these differences were resolved, other uncertainties would remain. The potential impact of these uncertainties can be usefully assessed by examining the effect of a change in any given assumption on the aggregate cost results, provided any correlation between variables is adequately dealt with.

10. Social learning and innovation, and changes in institutional structure could contribute to climate change mitigation. Changes in collective rules and individual behaviours may have significant effects on greenhouse gas emissions, but take place within a complex institutional, regulatory and legal setting. Several studies suggest that current incentive systems can encourage resource intensive production and consumption patterns that increase greenhouse gas emissions in all sectors, e.g. transport and housing. In the shorter term, there are opportunities to influence through social innovations individual and organizational behaviours. In the longer term such innovations, in combination with technological change, may further enhance socio-economic potential, particularly if preferences and cultural norms shift towards lower emitting and sustainable behaviours. These innovations frequently meet with resistance, which may be addressed by encouraging greater public participation in the decision-making processes. This can help contribute to new approaches to sustainability and equity (Sections 1.4.3, 5.3.8, 10.3.2, 10.3.4).

Other reports in this collection