Synthesis Report - Question 7

Climate Change 2001: Synthesis Report

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This question focuses on the potential for, and costs of, mitigation both in the near and long term. The issue of the primary mitigation benefits (the avoided costs and damages of slowing climate change) is addressed in Questions 5 and 6, and that of ancillary mitigation benefits is addressed in this response and the one to Question 8. This response describes a variety of factors that contribute to significant differences and uncertainties in the quantitative estimates of the costs of mitigation options. The SAR described two categories of approaches to estimating costs: bottom-up approaches, which often assess near-term cost and potential, and are built up from assessments of specific technologies and sectors; and top-down approaches, which proceed from macro-economic relationships. These two approaches lead to differences in the estimates of costs, which have been narrowed since the SAR. The response below reports on cost estimates from both approaches for the near term, and from the top-down approach for the long term. Mitigation options and their potential to reduce greenhouse gas emissions and sequester carbon are discussed first. This is followed by a discussion of the costs for achieving emissions reductions to meet near-term emissions constraints, and long-term stabilization goals, and the timing of reductions to achieve such goals. This response concludes with a discussion of equity as it relates to climate change mitigation.



Potential, Barriers, Opportunities, Policies, and Costs of Reducing Greenhouse Gas Emissions in the Near Term



Significant technological and biological potential exists for near-term mitigation.


Significant technical progress relevant to greenhouse gas emissions reduction has been made since the SAR, and has been faster than anticipated. Advances are taking place in a wide range of technologies at different stages of evelopment -- for example, the market introduction of wind turbines; the rapid elimination of industrial by-product gases, such as N2O from adipic acid production and perfluorocarbons from aluminum production; efficient hybrid engine cars; the advancement of fuel cell technology; and the demonstration of underground CO2 storage. Technological options for emissions reduction include improved efficiency of end-use devices and energy conversion technologies, shift to zero- and low-carbon energy technologies, improved energy management, reduction of industrial by-product and process gas emissions, and carbon removal and storage. Table 7-1 summarizes the results from many sectoral studies, largely at the project, national, and regional level with some at the global level, providing estimates of potential greenhouse gas emissions reductions to the 2010 and 2020 time frame.

WGIII TAR Sections 3.3-8, & WGIII TAR Chapter 3 Appendix

Forests, agricultural lands, and other terrestrial ecosystems offer significant carbon mitigation potential. Conservation and sequestration of carbon, although not necessarily permanent, may allow time for other options to be further developed and implemented (see Table 7-2). Biological mitigation can occur by three strategies: a) conservation of existing carbon pools, b) sequestration by increasing the size of carbon pools,13 and c) substitution of sustainably produced biological products (e.g., wood for energy-intensive construction products and biomass for fossil fuels). Conservation of threatened carbon pools may help to avoid emissions, if leakage can be prevented, and can only become sustainable if the socio-economic drivers for deforestation and other losses of carbon pools can be addressed. Sequestration reflects the biological dynamics of growth, often starting slowly, passing through a maximum, and then declining over decades to centuries. The potential of biological mitigation options is on the order of 100 Gt C (cumulative) by the year 2050, equivalent to about 10 to 20% of projected fossil-fuel emissions during that period, although there are substantial uncertainties associated with this estimate. Realization of this potential depends upon land and water availability as well as the rates of adoption of land management practices. The largest biological potential for atmospheric carbon mitigation is in subtropical and tropical regions.

WGIII TAR Sections 3.6.4 & 4.2-4, & SRLULUCF
Table 7-1: Estimates of potential global greenhouse gas emission reductions in 2010 and in 2020 (WGIII SPM Table SPM-1).
Historic Emissions in 1990
[Mt Ceq yr-1]
Historic Ceq Annual Growth Rate over 1990-1995 [%]
Potential Emission Reductions in 2010
[Mt Ceq yr-1]
Potential Emission Reductions in 2020
[Mt Ceq yr-1]
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 per t C but two suggest net direct costs will exceed US$50 per t C.
  CO2 only
  - Energy efficiency
  - Material efficiency







More than half available at net negative direct costs.
Costs are uncertain.
  Non-CO2 gases



N2O emissions reduction costs are US$0-10 per t Ceq.
  CO2 only
  Non-CO2 gases




Most reductions will cost between US$0-100 per t C eq with limited opportunities for negative net direct cost options.
  CH4 only




About 75% of the savings as CH4 recovery from landfills at net negative direct cost; 25% at a cost of US$20 per t Ceq.
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 US$200 per t Ceq.
supply and
  CO2 only




Limited net negative direct cost options exist; many options are available for less than US$100 per t Ceq.
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 methane landfill 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 WGIII TAR Chapter 3 for all six gases. It excludes non-energy related sources of CO2 (cement production, 160 Mt C; gas flaring, 60 Mt C; and land-use change, 600-1,400 Mt C) and energy used for conversion of fuels in the end-use sector totals (630 Mt C). If petroleum refining and coke oven gas were added, global year 1990 CO2 emissions of 7,100 Mt C would increase by 12%. 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 1,500-14,000 Mt C eq for the year 2010 and of 12,000-16,000 Mt Ceq for the year 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 t Ceq (except for Montreal Protocol gases) or options that will not be adopted through the use of generally accepted policies.

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