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Scientific-Technical Analyses of Impacts, Adaptations, and Mitigation of Climate Change those obtained through reduced energy use could be achieved through changes in energy sources.

Assessment Report. Strong policy measures would be required to achieve these potentials. Energy-related greenhouse gas emission reductions depend on the source of the energy, but reductions in energy use will in general lead to reduced greenhouse gas emissions.

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Process-related greenhouse gases including CO2, CH. N2O, halocarbons, and SF, are released during manufacturing and industrial processes, such as the production of iron, steel, aluminum, ammonia, cement, and other materials. Large reductions are possible in some cases. Measures include modifying production processes, eliminating solvents, replacing feedstocks, materials substitution, increased recycling, and reduced consumption of greenhouse gas-intensive materials. Capturing and utilizing CH, from landfills and sewage treatment facilities and lowering the leakage rate of halocarbon refrigerants from mobile and stationary sources also can lead to significant greenhouse gas emission reductions.

Industry. Energy use in 1990 was estimated to be 98-117 EJ,
and is projected to grow to 140-242 EJ in 2025 without new
measures. Countries differ widely in their current industrial ener-
gy use and energy-related greenhouse gas emission trends.
Industrial sector energy-related greenhouse gas emissions in
most industrialized countries are expected to be stable or
decreasing as a result of industrial restructuring and technologi-
cal innovation, whereas industrial emissions in developing coun-
tries are projected to increase mainly as a result of industrial
growth. The short-term potential for energy-efficiency improve-
ments in the manufacturing sector of major industrial countries
is estimated to be 25%. The potential for greenhouse gas emis-
sion reductions is larger. Technologies and measures for reduc-
ing energy-related emissions from this sector include improving
efficiency (e.g., energy and materials savings, cogeneration,
energy cascading, steam recovery, and use of more efficient 4.1.3.
motors and other electrical devices); recycling materials and
switching to those with lower greenhouse gas emissions; and
developing processes that use less energy and materials.

Energy Supply

This assessment focuses on new technologies for capital investment and not on potential retrofitting of existing capital stock to use less carbon-intensive forms of primary energy. It is technically possible to realize deep emissions reductions in the energy supply sector in step with the normal timing of investments to replace infrastructure and equipment as it wears out or becomes obsolete. Many options for achieving these deep reductions will also decrease the emissions of sulfur dioxide, nitrogen oxides, and volatile organic compounds. Promising approaches, not ordered according to priority, are described below.

Transportation. Energy use in 1990 was estimated to be
61-65 EJ, and is projected to grow to 90-140 EJ in 2025 with-
out new measures. Projected energy use in 2025 could be
reduced by about a third to 60-100 EJ through vehicles using
very efficient drive-trains, lightweight construction, and low
air-resistance design, without compromising comfort and per-
formance. Further energy-use reductions are possible through
the use of smaller vehicles; altered land-use patterns, transport
systems, mobility patterns, and lifestyles; and shifting to less
energy-intensive transport modes. Greenhouse gas emissions
per unit of energy used could be reduced through the use of 4.1.3.1.
alternative fuels and electricity from renewable sources. These
measures, taken together, provide the opportunity for reducing
global transport energy-related greenhouse gas emissions by
as much as 40% of projected emissions by 2025. Actions to
reduce energy-related greenhouse gas emissions from trans-
port can simultaneously address other problems such as local
air pollution.

Commercial/Residential Sector. Energy use in 1990 was estimated to be about 100 EJ, and is projected to grow to 165-205 EJ in 2025 without new measures. Projected energy use could be reduced by about a quarter to 126–170 EJ by 2025 without diminishing services through the use of energy efficient technology. The potential for greenhouse gas emission reductions is larger. Technical changes might include reduced heat transfers through building structures and more efficient space-conditioning and water supply systems, lighting, and appliances. Ambient temperatures in urban areas can be reduced through increased vegetation and greater reflectivity of building surfaces, reducing the energy required for space conditioning. Energy-related greenhouse gas emission reductions beyond

Greenhouse gas reductions in the use of fossil fuels

More Efficient Conversion of Fossil Fuels. New technology offers considerably increased conversion efficiencies. For example, the efficiency of power production can be increased from the present world average of about 30% to more than 60% in the longer term. Also, the use of combined heat and power production replacing separate production of power and heat-whether for process heat or space heating-offers a significant rise in fuel conversion efficiency.

Switching to Low-Carbon Fossil Fuels and Suppressing Emissions. Switching from coal to oil or natural gas, and from oil to natural gas, can reduce emissions. Natural gas has the lowest CO2 emissions per unit of energy of all fossil fuels at about 14 kg C/GJ, compared to oil with about 20 kg C/GJ and coal with about 25 kg C/GJ. The lower carbon-containing fuels can, in general, be converted with higher efficiency than coal. Large resources of natural gas exist in many areas. New, low capital cost, highly efficient combined-cycle technology has reduced electricity costs considerably in some areas. Natural gas could potentially replace oil in the transportation sector.

Scientific-Technical Analyses of Impacts, Adaptations, and Mitigation of Climate Change

Approaches exist to reduce emissions of CH, from natural gas pipelines and emissions of CH, and/or CO2 from oil and gas wells and coal mines.

Decarbonization of Flue Gases and Fuels, and CO, Storage. The removal and storage of CO2 from fossil fuel power-station stack gases is feasible, but reduces the conversion efficiency and significantly increases the production cost of electricity. Another approach to decarbonization uses fossil fuel feedstocks to make hydrogen-rich fuels. Both approaches generate a byproduct stream of CO2 that could be stored, for example, in depleted natural gas fields. The future availability of conversion technologies such as fuel cells that can efficiently use hydrogen would increase the relative attractiveness of the latter approach. For some longer term CO2 storage options, the costs, environmental effects, and efficacy of such options remain largely unknown.

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Switching to Renewable Sources of Energy. Solar, biomass, wind, hydro, and geothermal technologies already are widely used. In 1990, renewable sources of energy contributed about 20% of the world's primary energy consumption, most of it fuelwood and hydropower. Technological advances offer new opportunities and declining costs for energy from these sources. In the longer term, renewable sources of energy could meet a major part of the world's demand for energy. Power systems can easily accommodate limited fractions of intermittent generation, and with the addition of fast-responding backup and storage units, also higher fractions. Where biomass is sustainably regrown and used to displace fossil fuels in energy production, net carbon emissions are avoided as the CO2 released in converting the biomass to energy is again fixed in biomass through photosynthesis. If the development of biomass energy can be carried out in ways that effectively address concerns about other environmental issues and competition with other land uses, biomass could make major contributions in both the electricity and fuels markets, as well as offering prospects of increasing rural employment and income.

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billion by 2100. GDP grows 7-fold by 2050 (5-fold and 14-fold in industrialized and developing countries, respectively) and 25-fold by 2100 (13-fold and 70-fold in industrialized and developing countries, respectively), relative to 1990. Because of emphasis on energy efficiency, primary energy consumption rises much more slowly than GDP. The energy supply constructions were made to meet energy demand in (i) projections developed for the IPCC's First Assessment Report (1990) in a low energy demand variant, where global primary commercial energy use approximately doubles, with no net change for industrialized countries but a 4.4-fold increase for developing countries from 1990 to 2100; and (ii) a higher energy demand variant, developed in the IPCC IS92a scenario where energy demand quadruples from 1990 to 2100. The energy demand levels of the LESS constructions are consistent with the energy demand mitigation chapters of this Second Assessment Report. Figure 5 shows combinations of different energy sources to meet changing levels of demand over the next century. The analysis of these variants leads to the following conclusions:

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Deep reductions of CO2 emissions from energy supply systems are technically possible within 50 to 100 years, using alternative strategies.

Many combinations of the options identified in this assessment could reduce global CO2 emissions from fossil fuels from about 6 Gt C in 1990 to about 4 Gt C/yr by 2050, and to about 2 Gt C/yr by 2100 (see Figure 6). Cumulative CO2 emissions, from 1990 to 2100, would range from about 450 to about 470 Gt C in the alternative LESS constructions. Higher energy efficiency is underscored for achieving deep reductions in CO2 emissions, for increasing the flexibility of supply side combinations, and for reducing overall energy system costs.

Interregional trade in energy grows in the LESS constructions compared to today's levels, expanding sustainable development options for Africa, Latin America, and the Middle East during the next century.

Costs for energy services in each LESS variant relative to costs for conventional energy depend on relative future energy prices, which are uncertain within a wide range, and on the performance and cost characteristics assumed for alternative technologies. However, within the wide range of future energy prices, one or more of the variants would plausibly be capable of providing the demanded energy services at estimated costs that are approximately the same as estimated future costs for current conventional energy. It is not possible to identify a least-cost future energy system for the longer term, as the relative costs of options depend on resource constraints and technological opportunities that are imperfectly known, and on actions by governments and the private sector.

The literature provides strong support for the feasibility of achieving the performance and cost characteristics assumed for energy technologies in the LESS constructions, within the next 2 decades, though it is impossible to be certain until the research

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Scientific-Technical Analyses of Impacts, Adaptations, and Mitigation of Climate Change

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BI NI NGI CI HD

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BI= Biomass-Intensive Variant; NI = Nuclear-Intensive Variant; NGI = Natural Gas-Intensive Variant;
CI=Coal-Intensive Variant; HD = High-Demand Variant

Figure 5: Global primary energy use for alternative Low CO2-Emitting Energy Supply System (LESS) constructions: Alternatives for meeting different energy demand levels over time, using various fuel mixes.

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Scientific-Technical Analyses of Impacts, Adaptations, and Mitigation of Climate Change

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1990

BI NINGICI HD IS92 BI NINGICI HDIS92 BI NINGICI HD IS92 BI NINGICI HD IS92

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BI= Biomass-Intensive Variant; NI = Nuclear-Intensive Variant; NGI = Natural Gas-Intensive Variant;
CI=Coal-Intensive Variant; HD = High-Demand Variant

Figure 6: Annual energy-related CO, emissions for alternative LESS constructions, with comparison to the IPCC IS92a-f scenarios.

important role in reducing current emissions of CO2, CH, and NO and in enhancing carbon sinks. A number of measures could conserve and sequester substantial amounts of carbon (approximately 60-90 Gt C in the forestry sector alone) over the next 50 years. In the forestry sector, costs for conserving and sequestering carbon in biomass and soil are estimated to range widely but can be competitive with other mitigation options. Factors affecting costs include opportunity costs of land; initial costs of planting and establishment; costs of nurseries; the cost of annual maintenance and monitoring; and transaction costs. Direct and indirect benefits will vary with national circumstances and could offset the costs. Other practices in the agriculture sector could reduce emissions of other greenhouse gases such as CH, and N2O. Landuse and management measures include:

Sustaining existing forest cover Slowing deforestation

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The net amount of carbon per unit area conserved or sequestered in living biomass under a particular forest management practice and present climate is relatively well understood. The most important uncertainties associated with estimating a global value are (i) the amount of land suitable and available for forestation, regeneration, and/or restoration programs; (ii) the rate at which tropical deforestation can actually be reduced; (iii) the long-term use (security) of these lands; and (iv) the continued suitability of some practices for particular locations given the possibility of changes in temperature, water availability, and so forth under climate change.

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Regenerating natural forests

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Promoting agroforestry

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Cross-sectoral assessment of different combinations of mitiga

Altering management of agricultural soils and rangelands tion options focuses on the interactions of the full range of tech-
Improving efficiency of fertilizer use

nologies and practices that are potentially capable of reducing

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Scientific-Technical Analyses of Impacts, Adaptations, and Mitigation of Climate Change

emissions of greenhouse gases or sequestering carbon. Current analysis suggests the following:

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Competing Uses of Land, Water, and Other Natural Resources. A growing population and expanding economy will increase the demand for land and other natural resources needed to provide, inter alia, food, fiber, forest products, and recreation services. Climate change will interact with the resulting intensified patterns of resource use. Land and other resources could also be required for mitigation of greenhouse gas emissions. Agricultural productivity improvements throughout the world and especially in developing countries would increase availability of land for production of biomass energy.

Geoengineering Options. Some geoengineering approaches to counterbalance greenhouse gas-induced climate change have been suggested (e.g., putting solar radiation reflectors in space or injecting sulfate aerosols into the atmosphere to mimic the cooling influence of volcanic eruptions). Such approaches generally are likely to be ineffective, expensive to sustain, and/or to have serious environmental and other effects that are in many cases poorly understood.

Policy Instruments

Mitigation depends on reducing barriers to the diffusion and transfer of technology, mobilizing financial resources, supporting capacity building in developing countries, and other approaches to assist in the implementation of behavioral changes and technological opportunities in all regions of the globe. The optimum mix of policies will vary from country to country, depending upon political structure and societal receptiveness. The leadership of national governments in applying these policies will contribute to responding to adverse consequences of climate change. Governments can choose policies that facilitate the penetration of less greenhouse gas-intensive technologies and modified consumption patterns. Indeed, many countries have extensive experience with a variety of policies that can accelerate the adoption of such technologies. This experience comes from efforts over the past 20 to 30 years to achieve improved energy efficiency, reduce the environmental impacts of agricultural policies, and meet conservation and environmental goals unrelated to climate change. Policies to reduce net greenhouse gas emissions appear more easily implemented when they are designed to address other concerns that impede sustainable development (e.g., air pollution and soil erosion). A number of policies, some of which may need regional or international agreement, can facilitate the penetration of less greenhouse gas-intensive technologies and modified consumption patterns, including:

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Reducing or removing other subsidies (e.g., agricultural and transport subsidies) that increase greenhouse gas emissions

Tradable emissions permits

Voluntary programs and negotiated agreements with industry

Utility demand-side management programs

Regulatory programs, including minimum energyefficiency standards (e.g., for appliances and fuel economy)

Stimulating RD&D to make new technologies available Market pull and demonstration programs that stimulate the development and application of advanced technologies

Renewable energy incentives during market build-up Incentives such as provisions for accelerated depreciation and reduced costs for consumers

Education and training; information and advisory

measures

Options that also support other economic and environmental goals.

Accelerated development of technologies that will reduce greenhouse gas emissions and enhance greenhouse gas sinksas well as understanding the barriers that inhibit their diffusion into the marketplace-requires intensified research and development by governments and the private sector.

Authors/Reviewers

Robert T. Watson, USA; M.C. Zinyowera, Zimbabwe; Richard H. Moss, USA; Roberto Acosta Moreno, Cuba; Sharad P. Adhikary, Nepal, Michael Adler, USA; Shardul Agrawala, India; Adrian Guillermo Aguilar, Mexico; Saiyed Al-Khouli, Saudi Arabia: Barbara Allen-Diaz, USA; B. W. Ang. Singapore; Anne Arquit-Niederberger, Switzerland, Walter Baethgen, Uruguay, Martin Beniston, Switzerland; Luitzen Bijlsma, The Netherlands; Rosina Bierbaum, USA; Michel Boko, Republic of Benin; Bert Bolin,

Sweden; Sandra Brown, USA; Peter Bullock, UK; Melvin G.R. Cannell, UK; Osvaldo F.

Canziani, Argentina; Rodolfo Carcavallo, Argentina; William Chandler, USA; Fred C. Cheghe, Kenya. Vernon Cole, USA; Rex Victor Cruz, Philippines, Ogunlade Davidson, Sierra Leone, Sandra Diaz, Argentina: Andrew F. Dlugolecki, Scotland; James A. Edmonds, USA; Lin Erda, China, John Everett, USA; Zhou Fengqi, China; Andreas Fischlin, Switzerland; B. Blair Fitzharris, New Zealand, Douglas G. Fox, USA; Jaafar Friaa, Tunisia, Alexander Rauja Gacuhi, Kenya, W. Galinski, Poland, Habiba Gitay. Australia; Howard Gruenspecht, USA; Steven P. Hamburg, USA; Hisashi Ishitani, Japan; Venugopalan Ittekkot, Germany, Thomas B. Johansson, Sweden; Zdzisław Kaczmarek. Poland; Takao Kashiwagi, Japan, Miko Kirschbaum, Australia; Andrei Krovnin, Russian Federation, Richard J.T. Klein, The Netherlands; S.M. Kulshrestha, India; Herbert Lang. Switzerland; Henry Le Houerou, France, Rik Leemans, The Netherlands; Mark D. Levine, USA; Chunzhen Liu, China; Daniel Lluch-Belda, Mexico, Michael MacCracken, USA; Gabriel M. Mailu, Kenya, Kathy Maskell, UK: Roger F. McLean, Australia; Anthony J. McMichael, UK; Laurie Michaelis, France; Ed Miles, USA; William Moomaw, USA; Roberto Moreira, Brazil; Nebojsa Nakicenovic, Austria; Shuzo Nishioka, Japan; lan Noble, Australia; Leonard A. Nurse, Barbados; Rispa Odongo, Kenya; Mats Oquist, Sweden, Martin L. Parry, UK; Martha Perdomo, Venezuela; Michel Petit, France, P.S. Ramakrishnan, India; N.H. Ravindranath, India; John Reilly, USA: Arthur Riedacker, France, Hans-Holger Rogner, Canada; Jayant Sathaye, USA; Michael J. Scott, USA; Subodh K. Sharma, India; David Shriner, USA; S.K. Sinha, India, Jim F. Skea, UK; Allen M. Solomon, USA; Eugene Z. Stakhiv, USA; Oedon Starosolszky, Hungary, Su Jilan, China; Avelino Suarez, Cuba, Bo Svensson, Sweden, Hidekazu Takakura, Japan; Melissa Taylor, USA, Dennis Tirpak, USA; Viet Lien Tran, Vietnam: Jean-Paul Troadec, France, Hiroshi Tsukamoto, Japan; Itsuya Tsuzaka, Japan; Pier Vellinga, The Netherlands, Ted Williams, USA; Youyu Xie, China; Deying Xu, China; Patrick Young, USA

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