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Scientific-Technical Analyses of Impacts, Adaptations, and Mitigation of Climate Change Assessment Report. Strong policy measures would be required those obtained through reduced energy use could be achieved to achieve these potentials. Energy-related greenhouse gas through changes in energy sources. emission reductions depend on the source of the energy, but reductions in energy use will in general lead to reduced greenhouse gas emissions.

4.1.2. Mitigating Industrial Process and Human

Settlement Emissions 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 Process-related greenhouse gases including CO,, CH, N, O, measures. Countries differ widely in their current industrial ener- halocarbons, and SF, are released during manufacturing and gy use and energy-related greenhouse gas emission trends. industrial processes, such as the production of iron, steel, aluIndustrial sector energy-related greenhouse gas emissions in minum, ammonia, cement, and other materials. Large reducmost industrialized countries are expected to be stable or tions are possible in some cases. Measures include modifying decreasing as a result of industrial restructuring and technologi- production processes, eliminating solvents, replacing feedcal innovation, whereas industrial emissions in developing coun- stocks, materials substitution, increased recycling, and reduced tries are projected to increase mainly as a result of industrial consumption of greenhouse gas-intensive materials. Capturing growth. The short-term potential for energy efficiency improve and utilizing CH, from landfills and sewage treatment facilities ments in the manufacturing sector of major industrial countries and lowering the leakage rate of halocarbon refrigerants from is estimated to be 25%. The potential for greenhouse gas emis- mobile and stationary sources also can lead to significant sion reductions is larger. Technologies and measures for reduc- greenhouse gas emission reductions. 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. Energy Supply motors and other electrical devices); recycling materials and switching to those with lower greenhouse gas emissions; and This assessment focuses on new technologies for capital developing processes that use less energy and materials. investment and not on potential retrofitting of existing capital

stock to use less carbon-intensive forms of primary energy. It Transportation. Energy use in 1990 was estimated to be is technically possible to realize deep emissions reductions in 61-65 EJ. and is projected to grow to 90–140 EJ in 2025 with- the energy supply sector in step with the normal timing of out new measures. Projected energy use in 2025 could be investments to replace infrastructure and equipment as it wears reduced by about a third to 60-100 EJ through vehicles using out or becomes obsolete. Many options for achieving these very efficient drive-trains, lightweight construction, and low deep reductions will also decrease the emissions of sulfur dioxair-resistance design, without compromising comfort and per- ide, nitrogen oxides, and volatile organic compounds. formance. Further energy-use reductions are possible through Promising approaches, not ordered according to priority, are the use of smaller vehicles; altered land-use patterns, transport described below. 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. Greenhouse gas reductions in the use of fossil fuels alternative fuels and electricity from renewable sources. These measures, taken together, provide the opportunity for reducing More Efficient Conversion of Fossil Fuels. New technology global transport energy-related greenhouse gas emissions by offers considerably increased conversion efficiencies. For as much as 40% of projected emissions by 2025. Actions to example, the efficiency of power production can be increased reduce energy-related greenhouse gas emissions from trans- from the present world average of about 30% to more than port can simultaneously address other problems such as local 60% in the longer term. Also, the use of combined heat and air pollution.

power production replacing separate production of power and heat—whether for process heat or space heating

offers a sigCommercial/Residential Sector. Energy use in 1990 was esti- nificant rise in fuel conversion efficiency. mated to be about 100 EJ, and is projected to grow to 165–205 EJ in 2025 without new measures. Projected energy use could Switching Low-Carbon Fossil Fuels and Suppressing be reduced by about a quarter to 126-170 EJ by 2025 without Emissions. Switching from coal to oil or natural gas, and from diminishing services through the use of energy efficient tech- oil to natural gas, can reduce emissions. Natural gas has the nology. The potential for greenhouse gas emission reductions lowest CO2 emissions per unit of energy of all fossil fuels at is larger. Technical changes might include reduced heat trans- about 14 kg CIGJ, compared to oil with about 20 kg C/GJ and fers through building structures and more efficient space-con- coal with about 25 kg C/GJ. The lower carbon-containing fuels ditioning and water supply systems, lighting, and appliances. can, in general, be converted with higher efficiency than coal. Ambient temperatures in urban areas can be reduced through Large resources of natural gas exist in many areas. New, low increased vegetation and greater reflectivity of building sur- capital cost, highly efficient combined-cycle technology has faces, reducing the energy required for space conditioning. reduced electricity costs considerably in some areas. Natural Energy-related greenhouse gas emission reductions beyond gas could potentially replace oil in the transportation sector. Scientific-Technical Analyses of Impacts, Adaptations, and Mitigation of Climate Change

IS Approaches exist to reduce emissions of CH, from natural gas billion by 2100. GDP grows 7-fold by 2050 (5-fold and 14-fold pipelines and emissions of CH. and/or CO, from oil and gas in industrialized and developing countries, respectively) and wells and coal mines.

25-fold by 2100 (13-fold and 70-fold in industrialized and

developing countries, respectively), relative to 1990. Because Decarbonization of Flue Gases and Fuels, and CO, Storage of emphasis on energy efficiency, primary energy consumption The removal and storage of CO, from fossil fuel power-station rises much more slowly than GDP. The energy supply constack gases is feasible, but reduces the conversion efficiency structions were made to meet energy demand in (i) projections and significantly increases the production cost of electricity developed for the IPCC's First Assessment Report (1990) in a Another approach to decarbonization uses fossil fuel feed- low energy demand variant, where global primary commercial stocks to make hydrogen-rich fuels. Both approaches generate energy use approximately doubles, with no net change for a byproduct stream of CO, that could be stored, for example, industrialized countries but a 4.4-fold increase for developing in depleted natural gas fields. The future availability of con- countries from 1990 to 2100; and (ii) a higher energy demand version technologies such as fuel cells that can efficiently use variant, developed in the IPCC IS92a scenario where energy hydrogen would increase the relative attractiveness of the lat- demand quadruples from 1990 to 2100. The energy demand ter approach. For some longer term CO, storage options, the levels of the LESS constructions are consistent with the energy costs, environmental effects, and efficacy of such options demand mitigation chapters of this Second Assessment Report. remain largely unknown.

Figure S shows combinations of different energy sources to

meet changing levels of demand over the next century. The 4.13.2 Switching to non-fossil fuel sources of energy analysis of these variants leads to the following conclusions: Switching to Nuclear Energy. Nuclear energy could replace Deep reductions of CO2 emissions from energy supbaseload fossil fuel electricity generation in many parts of the ply systems are technically possible within 50 to 100 world if generally acceptable responses can be found to con- years, using alternative strategies. cerns such as reactor safety, radioactive-waste transport and Many combinations of the options identified in this disposal, and nuclear proliferation.

assessment could reduce global CO2 emissions from

fossil fuels from about 6 Gt C in 1990 to about 4 Gt Switching to Renewable Sources of Energy. Solar, biomass, Clyr by 2050, and to about 2 G1 C/yr by 2100 (see wind, hydro, and geothermal technologies already are widely Figure 6). Cumulative CO2 emissions. from 1990 to used. In 1990, renewable sources of energy contributed about 20% 2100, would range from about 450 to about 470 G C of the world's primary energy consumption, most of it fuelwood in the alternative LESS constructions. and hydropower. Technological advances offer new opportunities Higher energy efficiency is underscored for achieving and declining costs for energy from these sources. In the longer deep reductions in CO2 emissions, for increasing the term, renewable sources of energy could meet a major part of the flexibility of supply side combinations, and for reducworld's demand for energy. Power systems can easily accommo

ing overall energy system costs. date limited fractions of intermittent generation, and with the addi- Interregional trade in energy grows in the LESS contion of fast-responding backup and storage units, also higher frac

structions compared to today's levels, expanding sustions. Where biomass is sustainably regrown and used to displace tainable development options for Africa, Latin fossil fuels in energy production, net carbon emissions are avoid- America, and the Middle East during the next century. ed as the CO, released in converting the biomass to energy is again fixed in biomass through photosynthesis. If the development of Costs for energy services in each LESS variant relative to costs biomass energy can be carried out in ways that effectively address for conventional energy depend on relative future energy concerns about other environmental issues and competition with prices, which are uncertain within a wide range, and on the perother land uses, biomass could make major contributions in both formance and cost characteristics assumed for alternative techthe electricity and fuels markets, as well as offering prospects of nologies. However, within the wide range of future energy increasing rural employment and income.

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 4.1.4. Integration of Energy System Mitigation Options current conventional energy. It is not possible to identify a

least-cost future energy system for the longer term, as the relaTo assess the potential impact of combinations of individual mea- tive costs of options depend on resource constraints and techsures at the energy system level, in contrast to the level of indi- nological opportunities that are imperfectly known, and on vidual technologies, variants of a Low CO,-Emitting Energy actions by governments and the private sector. Supply System (LESS) are described. The LESS constructions are "thought experiments” exploring possible global energy systems. The literature provides strong support for the feasibility of

achieving the performance and cost characteristics assumed for The following assumptions were made: World population energy technologies in the LESS constructions, within the next grows from 5.3 billion in 1990 to 9.5 billion by 2050 and 10.5 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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Solar H2

Biomass

Oil

Nuclear

Int. Renewables

Hydro

Natural Gas

Coal

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 CO,-Emitting Energy Supply System (LESS) constructions: Alternatives for meeting different energy demand levels over time, using various fuel mixes.

and development is complete and the technologies have been for emissions reductions would require more detailed analysis tested in the market. Moreover, these performance and cost of options, taking into account local conditions. characteristics cannot be achieved without a strong and sustained investment in research, development, and demonstration Because of the large number of options, there is flexibility as (RD&D). Many of the technologies being developed would to how the energy supply system could evolve, and paths of need initial support to enter the market, and to reach sufficient energy system development could be influenced by consideravolume to lower costs to become competitive.

tions other than climate change, including political, environ

mental (especially indoor and urban air pollution, acidification, Market penetration and continued acceptability of different and land restoration), and socioeconomic circumstances. energy technologies ultimately depends on their relative cost, performance (including environmental performance), institutional arrangements, and regulations and policies. Because 4.2. Agriculture, Rangelands, and Forestry costs vary by location and application, the wide variety of circumstances creates initial opportunities for new technologies Beyond the use of biomass fuels to displace fossil fuels, the manto enter the market. Deeper understanding of the opportunities agement of forests, agricultural lands, and rangelands can play an

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

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Net Energy-Related CO2 Emissions

CO2 Sequestered in Depleted
(Gross Emissions less CO, Sequestered)

Natural Gas Wells, etc.
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 CO2 emissions for alternative LESS constructions, with comparison to the IPCC IS92a-f scenarios.

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important role in reducing current emissions of CO2, CH, and Restoring degraded agricultural lands and rangelands N20 and in enhancing carbon sinks. A number of measures could Recovering CH, from stored manure conserve and sequester substantial amounts of carbon (approxi- Improving the diet quality of ruminants. mately 60-90 Gt C in the forestry sector alone) over the next 50 years. In the forestry sector, costs for conserving and sequester- The net amount of carbon per unit area conserved or ing carbon in biomass and soil are estimated to range widely but sequestered in living biomass under a particular forest mancan be competitive with other mitigation options. Factors affect- agement practice and present climate is relatively well undering costs include opportunity costs of land; initial costs of plant- stood. The most important uncertainties associated with estiing and establishment; costs of nurseries; the cost of annual main- mating a global value are (i) the amount of land suitable and tenance and monitoring, and transaction costs. Direct and indirect available for forestation, regeneration, and/or restoration probenefits will vary with national circumstances and could offset grams; (ii) the rate at which tropical deforestation can actually the costs. Other practices in the agriculture sector could reduce be reduced; (iii) the long-term use (security) of these lands; and emissions of other greenhouse gases such as CH, and NGO. Land- (iv) the continued suitability of some practices for particular use and management measures include:

locations given the possibility of changes in temperature, water

availability, and so forth under climate change.
Sustaining existing forest cover
Slowing deforestation
Regenerating natural forests

4.3. Cross-Sectoral Issues
Establishing tree plantations
Promoting agroforestry

Cross-sectoral assessment of different combinations of mitiga-
Altering management of agriculural 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 Reducing or removing other subsidies (e.g., agriculanalysis suggests the following:

tural and transport subsidies) that increase greenhouse

gas emissions Competing Uses of Land, Water, and Other Tradable emissions permits Natural Resources. A growing population and Voluntary programs and negotiated agreements with expanding economy will increase the demand for land

industry and other natural resources needed to provide, inter Utility demand-side management programs alia, food, fiber, forest products, and recreation ser- Regulatory programs, including minimum energyvices. Climate change will interact with the resulting

efficiency standards (e.g., for appliances and fuel intensified patterns of resource use. Land and other

economy) resources could also be required for mitigation of

Stimulating RD&D to make new technologies available greenhouse gas emissions. Agricultural productivity

Market pull and demonstration programs that stimuimprovements throughout the world and especially in late the development and application of advanced developing countries would increase availability of technologies land for production of biomass energy.

Renewable energy incentives during market build-up Geoengineering Options. Some geoengineering

Incentives such as provisions for accelerated depreciapproaches to counterbalance greenhouse gas-induced ation and reduced costs for consumers climate change have been suggested (e.g., putting Education and training; information and advisory solar radiation reflectors in space or injecting sulfate

.

measures aerosols into the atmosphere to mimic the cooling Options that also support other economic and enviinfluence of volcanic eruptions). Such approaches

ronmental goals. generally are likely to be ineffective, expensive to sustain, and/or to have serious environmental and other Accelerated development of technologies that will reduce effects that are in many cases poorly understood. greenhouse gas emissions and enhance greenhouse gas sinks

as well as understanding the barriers that inhibit their diffusion

into the marketplace-requires intensified research and devel4.4. Policy Instruments

opment by governments and the private sector.

Authors Reviewers

Mitigation depends on reducing barriers to the diffusion and
transfer of technology, mobilizing financial resources, support-
ing 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 recep-
tiveness. The leadership of national governments in applying
these policies will contribute to responding to adverse conse-
quences 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 environ-
mental 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 penetra-
tion of less greenhouse gas-intensive technologies and modi-
fied consumption patterns, including:

Robert T. Watson, USA; M.C. Zinyowera, Zimbabwe, Richard H. Moss, USA; Roberto
Acosta Moreno, Cuba: Sharad P. Adhikary. Nepal; Michael Adler, USA; Shardal
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 Benia, Bert Bolin
Sweden; Sandra Brown, USA; Peter Bullock, UK, Melvin G.R. Canaell, UK; Osvaldo F.
Canziani, Argentina: Rodolfo Carcavallo, Argentina, William Chandler, USA; Fred C.
Cheghe, Kenya, Vernon Cok, USA, Re Victor Cruz, Philippines, Ogunlade Davidson
Sierra Leone Sandra Diaz, Argentina: Andrew F. Dlugolechi, Scotland, James A
Edmonds, USALin Erda. China: Joha Everett, USA. Zhou Fengqi. China, Andreas
Fischlin, Switzerland, B. Blair Fitzharris, New Zealand; Douglas G. Fox, USA, Jaafar
Frian. Tunisia, Alexander Rauja Gacuhi, Kenya, W. Galinski, Poland, Habiba Gitay.
Australia, Howard Gruenspecht, USA, Steven P. Hamburg. USA: Hisashi Ishitani, Japan;
Venugopalan Insekkol, Germany. Thomas B. Johansson, Sweden, Zdzislaw Kaczmarek,
Poland, Takao Kashiwagi, Japan, Miko Kirschbaum. Australia, Andrei Krovnia, Russian
Federation, Richard J.T. Klein, The Netherlands, S.M. Kulshrestha, India: Herbert Lang
Switzerland, Henry Le Houeron, France: Rik Leemans, The Netherlands; Mart 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 Moomax, USA;
Roberto Moreira, Brazil, Nebojsa Nakicenovic, Austria. Shuzo Nishioka Japua, lan
Noble, Australia, Leonard A. Nurse, Barbados, Rispa Odongo, Kenya, Mats Oquial
Sweden, Martin L Parry, UK, Martha Perdomo, Venezuela: Michel Pecil France, PS.
Ramakrishnan, India, N.H Ravindranath, India: John Reilly, USA, Arthur Riedecker,
France, Hans-Holger Rogner, Canada: Jayant Sathaye, USA; Michael J. Scot, USA:
Subodh K. Sharma, India, David Shriner, USA, S.K Sinha, India, Jim F. Sken, UK: Allee
M. Solomon, USA, Eugene 2 Stakhiv, USA; Oedon Surosolszky, Hungary. Se Jilan.
China, Avelino Suarez, Cuba, Bo Svensson, Sweden: Hidekazu Takakur Japan, Melissa
Taylor, USA, Dennis Tirpak. USA: Viet Lien Tran, Vietnam: Jean-Paul Troadec, France,
Hiroshi Tsukamoto, Japan; Itsuya Tsuzaka, Japan; Pier Vellingn, The Netherlands, Ted
Williams. USA: Youyu Xic, China: Deying Xu, China: Patrick Young. USA

Putting in place appropriate institutional and structur-
al frameworks
Energy pricing strategies (e.g., carbon or energy

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