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4.10 Given cumulative emissions, and IPCC IS92a population and economic scenarios for 19902100, global annual average carbon dioxide emissions can be derived for the stabilization scenarios on a per.capita or per unit of economic activity basis. If the atmospheric concentration is to remain below 550 ppmv, the future global annual average emissions cannos, during the next century, exceed the current global average and would have to be much lower before and beyond the end of the next century. Global annual average emissions could be higher for stabilization levels of 750 to 1000 ppmv. Nevertheless, even to achieve these latter stabilization levels, the global annual average emissions would need to be less than 50% above current levels on a per capita basis or less than half of current levels per unit of economic activity'?.
4.11'3 The global average annual per capita emissions of carbon dioxide due to the combustion of fossil fuels is at present about 1.1 tonnes (as carbon). In addition, a net of about 0.2 tonnes per capita are emitted from deforestation and land-use change. The average annual fossil fuel per capita emission in developed and transitional economy countries is about 2.8 tonnes and ranges from 1.5 to 5.5 tonnes. The figure for the developing countries is 0.5 tonnes ranging from 0.1 tonnes to, in some few cases, above 2.0 tonnes (all figures are for 1990).
4.12" Using World Bank estimates of GDP (gross domestic product) al market exchange rates, the current global annual average emission of energy-related carbon dioxide is about 0.3 tonnes per thousand 1990 US dollars output. In addition, global net emissions from land use changes are about 0.05 tonnes per thousand US dollars of output. The current average annual energy-related emissions per thousand 1990 US dollars output, evaluated at market exchange rates, is about 0.27 tonnes in developed and transitional economy countries and about 0.41 tonnes in developing countries. Using World Bank estimates of GDP at purchasing power parity exchange rates, the average annual energy-related emissions per thousand 1990 US dollars output is about 0.26 tonnes in developed and transitional economy countries and about 0.16 tonnes in developing countries."
4.13 Atmospheric methane concentrations adjust to changes in anthropogenic emissions over a period of 9 to 15 years. If the annual methane emissions were immediately reduced by about 30 Tg CH. (about 8% of current anthropogenic emissions) methane concentrations would remain a today's levels. If methane emissions were to remain constant at their current levels, its concentration (1720 ppbv in 1994) would rise to about 1820 ppbv over the next 40 years.
China registered its disagreement on the use of carbon dioxide emissions derived on the basis of a per unit of economic activity.
The Panel agreed that this paragraph shall not prejudge the current negociacions under the
The Panel agreed that this paragraph shall not prejudge the current negociacions under the
These calculations of emissions per unit of economic activicy do not include emissions from land use changes or adjustments to reflect the informal economy.
4.14 Nitrous oxide has a long lifetime (about 120 years) In order for the concentration to be stabilized near current levels (312 ppbv in 1994), anthropogenic sources would need to be reduced immediately by more than 50%. If emissions of nitrous oxide were held constant at current levels, its concentration would rise to about 400 ppbv over several hundred years, which would increase its incremental radiative forcing by a factor of four over its current level.
Further points on stabilization
4.15 Stabilization of the concentrations of very long-lived gases, such as SF. or perfluorocarbons, can only be achieved effectively by stopping emissions.
4.16 The importance of the contribution of CO2 to climate forcing, relative to that of the other greenhouse gases, increases with time in all of the IS92 emission scenarios (a to 1). For example, in the IS92a scenario, the CO, contribution increases from the present 60% to about 75% by the year 2100. During the same period, methane and nitrous oxide forcings increase in absolute terms by a factor that ranges between two and three.
4.17 The combined effect of all greenhouse gases in producing radiative forcing is often expressed in terms of the equivalent concentration of carbon dioxide which would produce the same forcing. Because of the effects of the other greenhouse gases, stabilisation at some level of equivalent carbon dioxide concentration implies maintaining carbon dioxide concentration at a lower level.
4.18 The stabilization of greenhouse gas concentrations does not imply that there will be no further climate change. After stabilization is achieved, global mean surface temperature would continue to rise for some centuries and sea level for many centuries.
TECHNOLOGY AND POLICY OPTIONS FOR MITIGATION
5.1 The IPCC Second Assessment Report (1995) examines a wide range of approaches to reduce emissions and enhance sinks of greenhouse gases. This section provides technical information on options that could be used to reduce anthropogenic emissions and enhance sinks. of the principal greenhouse gases with a view to stabilizing their atmospheric concentrations; however, this analysis does not attempt to quantify potential macroeconomic consequences that may be associated with mitigation
5.2 Significant reductions in net greenhouse gas emissions are technically possible and can be economically feasible. These reductions can be achieved by utilizing an extensive array of technologies and policy measures that accelerate technology developmen, diffusion, and transfer in all sectors, including the energy, industry, transportation, residential commercial and agricultural/forestry sectors.
5.3 The degree to which technical potential and cost-effectiveness are realized is dependent on initiatives to counter lack of information and overcome cultural, institutional, legal, financial and economic barriers which can hinder diffusion of technology or behavioural changes. 5.4 By the year 2100, the worid's commercial energy system in effect will be replaced at least twice, offering opportunities to change the energy system without premature retirement of capital stock; significant amounts of capital stock in the industrial, commercial, residential, and agricultural/forestry sectors will also be replaced. These cycles of capital replacement provide opportunities to utilize new, better performing technologies.
The IPCC projects (IPCC 1992; IPCC 1994) that without policy intervention, there could be significant growth in emissions from the industrial, transportation, and commercial residential buildings sectors. Numerous studies have indicated that 10-30% energy efficiency gains above present levels are feasible at negative's to zero cost in each of the sectors in many parts of the world through technical conservation measures and improved management practices over the next 2 to 3 decades. Using technologies that presently yield the highest output of energy services for a given input of energy, efficiency gains of 50–60% would be technically feasible in many countries over the same time period. Achieving these potentials will depend on future cost reductions, the rate of development and implementation of new technologies, financing and technology transfer, as well as measures to overcome a variety of non-technical barriers. Because energy use is growing worldwide, even replacing current technology with more efficient technology could still lead to an absolute increase in greenhouse gas emissions in the future. Technologies and measures to reduce greenhouse gas emissions in energy end-use sectors include:
Industry: improving efficiency; recycling materials and switching to those with lower
Energy Supply 5.6 It is technically possible to realize deep emissions reductions in the energy supply sector within 50 to 100 years using alternative strategies, in step with the normal timing of investments to replace infrastructure and equipment as it wears out or becomes obsolete. Promising approaches, not ordered according to priority, include:
Greenhouse gas reductions in the use of fossil fuels
Switching to nuclear energy (if generally acceptable responses can be found to concerns
Integration of Energy System Mitigation Options
5.7 The potential for greenhouse gas emission reductions exceeds the potential for energy use efficiency because of the possibility of switching fuels and energy sources, and reducing the demand for energy services. Even greater energy efficiency, and hence reduced greenhouse gas emissions, could be attained with comprehensive energy source-to-service chains.
5.8 To assess the potential impact of combinations of individual measures at the energy systems level, “thought experiments” exploring variants of a low-CO, emitting energy supply system were described. These variants illustrate the technical possibility of deep reductions in CO2 emissions from the energy supply system within 50 to 100 years using alternative strategies. These exercises indicate the technical possibility of reducing annual global emissions from 6 GtC in 1990 to about 4 GtC in 2050 and to about 2 GtC by 2100. Cumulative CO2 emissions from 1990 to 2100 would range from about 450 GTC to about 470 GC in these constructions, thus keeping atmospheric concentrations below 500 ppmv.
5.9 Costs for integrated energy services 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. Improving energy efficiency, and a strong and sustained investment in research, development, and demonstration to encourage transfer and diffusion of alternative energy supply technologies and improvements in energy efficiency is critical to deep reductions in greenhouse
gas emissions. Many of the technologies being developed would need initial support to enter the market, and to reach sufficient volume to lower costs to become competitive.
5.10 Market penetration and continued acceptability of different energy technologies ultimately depends on their relative cost, performance (including environmental performance), institutional arrangements, and regulations and policies. Because costs vary by location and application, the wide variety of circumstances creates initial opportunities for new technologies to enter the market. Deeper understanding of the opportunities for emissions reductions would require more detailed analysis of options, taking into account local conditions.
Industrial Process and Human Settlement Emissions
5.11 Large reductions are possible in some cases in process-related greenhouse gases including CO2, CH, N2O, halocarbons and SF6, released during manufacturing and industrial processes, such as production of iron, steel, aluminum, ammonia, cement and other materials. Measures include modifying production processes, eliminating solvents, replacing feedstocks, materials substitution, increased recycling, and reduced consumption of greenhouse gas-intensive materials. Capturing and utilizing methane 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.
Agriculture, Rangelands. and Forestry
5.12 Beyond the use of biomass fuels to displace fossil fuels, the management of forests, agricultural lands, and rangelands can play an important role in reducing current emissions of carbon dioxide, methane, and nitrous oxide and enhancing carbon sinks. A number of measures could conserve and sequester substantial amounts of carbon (approximately 60-90 GtC in the foresty sector alone) over the next 50 years. In the forestry sector, measures include sustaining existing forest cover; slowing deforestation; natural forest regeneration; establishment of tree -plantations; promoting agroforestry. Other practices in the agriculture sector could reduce emissions of other greenhouse gases such as methane and nitrous oxide. 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.
5.13 The availability of low carbon technologies is a prerequisite for, but not a guarantee of, the ability to reduce greenhouse gas emissions at reasonable cost. Mitigation of emissions depends on reducing barriers to the diffusion and transfer of technology, mobilizing financial resources, supporting capacity building in developing countries and countries with economies in transition, and other approaches to assist in the implementation of behavioural changes and technological opportunities in all regions of the globe. The optimum mix of policies will vary from country to country, depending upon their energy markets, economic considerations, political structure and societal receptiveness. The leadership of national governments in applying these policies will contribute to responding to the adverse consequences of climate change. Policies to reduce nel greenhouse gas emissions appear more easily implemented when they are