Overview of the Portfolio
Carbon emissions (C) can be represented as the product of gross domestic product (GDP) and carbon emissions per unit GDP (C/GDP), that is, C = GDP X (C/GDP). The growth rate of GDP today is roughly 2.5 percent per year. Stabilizing CO2 emissions in a world whose GDP increases 2—3 percent per year requires comparable or greater percentage reductions in C/GDP. Stabilizing CO2 concentrations ultimately requires making deep long-term cuts in CO2 emissions (Houghton et al. 2001).
C/GDP can be expressed as the product of the amount of CO2 (or CO2-equivalents) emitted per unit of energy consumed (C/E) and the amount of energy consumed per unit GDP (E/GDP), that is, (C/GDP) = (C/E) X (E/GDP). Reduction in C/E can be accomplished by using renewable fuels (solar, wind, biomass, etc.), using fossil fuels with carbon sequestration, reducing C-equivalent emissions of non-CO2 greenhouse gases, or using nuclear power or potential future sources such as fusion power. Reduction in E/GDP can be accomplished by developing, for example, more efficient appliances, vehicles, buildings, and industrial processes (i.e., device efficiency), and by developing, for example, urban centers that lend themselves to more efficient transportation systems (i.e., systems efficiency).
Table 5.1 shows energy system and biophysical options categorized by how quickly a significant fraction of each option's total potential could be realized (columns) and by the potential magnitude of CO2 mitigation or its radiative equivalent (rows). This table identifies many options that we can begin deploying now and that can make a significant contribution over the coming decades. Research and development undertaken now can produce the additional options needed to stabilize climate on a longer timescale. In Table 5.2 we indicate the readiness of various options for deployment, as well the magnitude of carbon emissions that could be mitigated by each option. Furthermore, we indicate our subjective appraisal of the relative size of the research and development budget that should be allocated to each option. We believe that highest allocations should go to the most promising options that are limited now by unresolved, but tractable, scientific or technological issues (e.g., energy distribution systems that can facilitate large-scale wind and solar power, improved energy production efficiency, and fossil-fuel carbon capture
Table 5.1. Categorization of mitigation options by timescale to achieve a significant proportion of possible reductions (columns) and by potential magnitude of CO2 equivalent impact on radiative forcing (rows)
Rapidly deployablea
Not rapidly deployableb
Minor contributor < 3%
Major contributor > 3%
Biomass co-fire in coal-fired power plants Cogeneration (smallscale distributed)
Expanded use of natural gas combined cycle Hydropower Wind without storage (=10% of electric grid) Niche options: wave and tidal, geothermal, smallscale solar
Carbon storage in agricultural soils (no-till cultivation, cover crops)
Improved appliance, lighting, and motor efficiency Improved buildings Improved industrial processes Improved vehicle efficiency Non-CO2 gas abatement from industrial sources including coal mines, landfills, pipelines Non-CO2 gas abatement from agriculture including soils, animal industry Reforestation/land restoration Stratospheric sulfate aerosol geoengineering
Building-integrated photovoltaics Forest management/ fire suppression Ocean fertilization
Biomass to hydrogen or electricity possibly with carbon capture and sequestration Biomass to transportation fUel Cessation of net deforestation Energy-efficient urban and transportation system design Fossil-fuel carbon separation with geologic or ocean storage Highly efficient coal technologies (e.g., IGCC) Large-scale solar (with H2, long-distance transmission, storage)
Next-generation nuclear fission
Reduced population growth Wind (with H2, long-distance transmission, storage) Speculative technologies (direct atmospheric scrubbing, space solar, fusion, exotic geo-engineering, bioengineering)
Note: Minor contributors are capable of contributing <0.2 PgC y-1; major contributors> 0.2 PgC y-1. The left column represents technologies that can achieve a significant fraction of their potential within a few decades. The right column represents technologies that could be available in the coming decades if research and development begin now.
aA significant fraction of option's potential could be achieved within a few decades. bUnlikely to achieve a significant fraction of option's potential within a few decades.
Table 5.2. Magnitude of R&D needed driven by CO2 mitigation needs
Options
Magnitude of Longevity of preferred potential of energy Economic Technical R&D
contribution source efficiency readiness allocation Comments
Rapidly deployable, minor potential < 3% (< 0.2 PgCy-1) and< 20years Biomass co-fire in coal-fired power plants Cogeneration (small-scale distributed) Expanded use of natural gas combined cycle
Hydropower Wind
Niche options: wave and tidal, geothermal, small-scale solar
Conversion is straightforward Principal obstacles are regulatory Economic considerations are already driving adoption of this option; attractiveness depends on price and availability of natural gas Siting, relicensing, ecosystem disruption
Limits imposed by dispatch in power systems, resource availability
Rapidly déployable, major potential > 3% (> 0.2Pg Cy^1) and = 20years Carbon storage in agricultural soils (no-till cultivation, cover crops)
Improved appliance, lighting, and motor efficiency
Improved buildings
Improved industrial processes
Improved vehicle efficiency
Non-CO, gas abatement from industrial sources including coal mines, landfills, pipelines
Non-CO, gas abatement from agriculture including soils, animal industry
Reforestation/land restoration
Stratospheric sulfate aerosol geoengineering
Verification, incentives, research into persistence of stored carbon; can be driven by nonclimate considerations Many possibilities, principal issue is incentives and public communication; can be driven by nonclimate considerations
Zoning, codes, and construction practice are important, higher capital requirements; can be driven by nonclimate considerations Many possibilities, principal issue is incentives; can be driven by nonclimate considerations Regulatory environment more important than technology; can be driven by nonclimate considerations Principal issues are regulation, cost, and incentives
Verification; Research on nitrogen cycling
Verification; land competition; win-win possibilities Issues of public acceptance, international law and unintended consequences
(continued)
Table 5.2. (continued)
Options
Not rapidly deployable, minor potential = 3% (= 0.2 PgC y1) and > 20years Building-integrated photovoltaics
Forest management/fire suppression
Magnitude of Longevity potential of energy contribution source
Ocean fertilization
Not rapidly deployable, major potential > 3% (> 0.2PgCy'1) and > 20years Biomass to hydrogen or electricity possibly with carbon capture and sequestration
Biomass to transportation fuel
Cessation or possible reversal of net deforestation Energy-efficient urban and transportation system design
Relative size ofprefetred Economic Technical R&D efficiency readiness allocation Comments
Primary research issue is system cost reduction
Win-win possibilities, but potential ecological costs, enhanced long-term fire vulnerability, questions about long-term effectiveness Issues include public acceptance, verification, efficacy, and unintended consequences
•• •• •• Large land requirements with potential landscape and ecological consequences; potential for negative net emissions ••• •• •• Large land requirements with potential landscape ecological consequences ••• ••• • Social/economic/political factors are limiting
<••• ••• • Social/economic/political factors are limiting
Fossil-fuel carbon separation and transport with geologic or ocean storage
Highly efficient coal technologies (e.g., IGCC)
Large-scale solar (with H2, long-distance transmission, storage)
Next-generation nuclear fission
Reduced population growth
Wind (with H2, long-distance transmission, storage)
Speculative technologies (direct atmospheric scrubbing, space solar, fusion, exotic geoengineering, bioengineering)
Unintended consequences, leakage, public acceptance; development of cost-effective H2 use technologies Need process improvements and cost reduction
Principal research costs in low-cost cell design, energy storage, transport Principally limited by public acceptance
Social/economic/political factors are limiting
Principal research costs in storage and transmission not in turbine design
Note: Many important options have relatively low R&D needs. Description of symbols: Magnitude of potential: • = could be a minor contributor (< 0.2 PgC y 1), •• = could be a major contributor (> 0.2 PgC y-1) but inadequate to be entire solution, ••• = could be entire solution (i.e., contribute > 20 PgC y-1). Longevity: • = most of potential could be exhausted this century, •• = most of potential could be exhausted over this millennium, ••• = could be sustained for many millennia. Economic efficiency as measured by cost per ton C avoided as measured against current mix of energy production: • = > US$150, •• = between US$50 and US$150, ••• = < US$50 and in a few cases negative. Readiness: • = not ready, •• = ready after additional R&D, ••• = ready. R&D needs: • = modest, •• = significant, ••• = major.
Figure 5.1. Cost of electricity presented as function of CO2 emissions per unit energy produced. Lower carbon emission technologies are generally more expensive. Costs per ton of carbon avoided can be estimated from the slope of the line connecting the initial electricity generation technology to the lower carbon emission technology (redrawn from Keith and Morgan 2002). Symbols: • = primary energy, o = Liquid transportation fuel, A = electricity, * = hydrogen. CCS refers to carbon capture and storage.
0 10 20 30 40 50 60 70 Carbon intensity (kgC GJ-1)
Figure 5.1. Cost of electricity presented as function of CO2 emissions per unit energy produced. Lower carbon emission technologies are generally more expensive. Costs per ton of carbon avoided can be estimated from the slope of the line connecting the initial electricity generation technology to the lower carbon emission technology (redrawn from Keith and Morgan 2002). Symbols: • = primary energy, o = Liquid transportation fuel, A = electricity, * = hydrogen. CCS refers to carbon capture and storage.
and storage). Figure 5.1 illustrates estimated carbon emission avoidance costs associated with moving to lower-carbon-emissions energy systems.
In the following sections, we review opportunities to reduce energy demand, to improve energy production efficiency, to develop renewable energy sources, to capture and sequester carbon, to reduce the emissions of non-CO2 greenhouse gases, and to mitigate climate change using fission power, geoengineering, and other options.
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