|Working Group III: Mitigation|
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Technologies and measures to reduce greenhouse gas emissions are continuously being developed (Nadel et al., 1998; National Laboratory Directors, 1997; PCAST, 1997; Martin et al., 2000). Many of these technologies focus on improving the efficiency of fossil fuel use since more than two-thirds of the greenhouse gas emissions addressed in the Kyoto Protocol (in carbon dioxide equivalents) are related to the use of energy. Energy intensity (energy consumed divided by gross domestic product (GDP)) and carbon dioxide intensity (CO2 emitted from burning fossil fuels divided by the amount of energy produced) have been declining for more than 100 years in developed countries without explicit government policies for decarbonization and both have the potential to decline further. Non-fossil fuel energy sources are also being developed and implemented as a means of reducing greenhouse gas emissions. Physical and biological sequestration of CO2 can potentially play a role in reducing greenhouse gas emissions in the future. Other technologies and measures focus on reducing emissions of the remaining major greenhouse gases - methane, nitrous oxide, hydrofluorocarbons (HFCs), perfluorocarbons (PFCs), and sulphur hexafluoride (SF6) (see Section 3.5 and Appendix to this Chapter).
Table 3.1 shows energy consumption in the four end-use sectors of the global economy industry, buildings, transport, and agricultureover time1. Data are displayed for six world regions developed countries, countries with economies in transition (EITs), developing Asia-Pacific countries, Africa, Latin America and the Middle East. Comparing global annual average growth rates (AAGRs) for primary energy use in the period 1971 to 1990 and 1990 to 1995 a significant decrease is noticed from 2.5% in the first period to about 1.0% in the latter, due almost entirely to the economic crisis in the EITs. Overall, growth averaged about 2.0% per year from 1971 to 1995. Table 3.1 also shows carbon dioxide emissions from energy consumption for four world regions. The AAGR of global carbon dioxide emissions from the use of energy also declined (from 2% to 1%) in the same periods. A different picture emerges if the countries with economies in transition are excluded. In this case, growth in world energy use averaged about 2.5% per year in both the 1971 to 1990 and 1990 to 1995 periods, while average annual growth in carbon dioxide emissions was 2.0% and 2.6% during the same time periods, respectively.
Uncertainty in Table 3.1 arises in a number of areas. First, the quality of energy data from the International Energy Agency (IEA) is not homogeneous because of the use of various reporting mechanisms and official sources of national data (IEA, 1997a; IEA, 1997b; IEA, 1997c)2. Second, for the economies in transition, primary energy use data and carbon dioxide data are from two different sources (BP, 1997; IEA, 1997a; IEA, 1997b; IEA, 1997c). There are inconsistencies between the two sources, and no analysis has yet been done to resolve them. Third, IEA statistics report sectoral data for the industrial and transport sectors, but not for buildings and agriculture, which are reported as other. These sectors have been estimated using an allocation scheme described in Price et al. (1998)3. In general, the most uncertainty is associated with data for the economies in transition region, and for the commercial and residential sub-categories of the buildings sector in all regions.
It is likely that total commercial energy production and demand estimates will be known accurately for most developed countries (within one or a few per cent), relatively accurately for some developing countries (with an uncertainty of 1% to 5%), and less accurately for developing countries with poorly functioning data gathering and statistical systems. Converting the energy data into carbon emissions introduces some increased uncertainty primarily as a consequence of the fraction of natural gas that leaks to the atmosphere and the fraction of all fossil fuels that are left uncombusted the uncertainty in carbon emissions is greater than that of energy use. Uncertainties in non-CO2 greenhouse gas emissions are greater than those for carbon emissions.
In general, energy supply statistics, and their disaggregation into fuel types, are more reliable than statistics for energy demand. In particular, the estimates of sectoral energy demand (buildings, industry, transportation, agriculture) and the further disaggregation into subsectors (e.g., residential and commercial buildings; auto transportation; specific industries), and then into end uses has relatively high levels of uncertainty for at least two reasons. First, the full data to perform these disaggregations are rarely gathered at the national level, so that assumptions and approximations need to be made. Second, the conventions vary among different countries as to what energy use belongs to which sector or subsector (e.g., the distinction between residential and commercial buildings; the issue of whether energy use in industrial buildings counts as industrial or building energy use).
The least accurate data are for non-commercial energy use, especially in developing countries dung, plant or forest waste, logs, and crops used for energy. Energy use from these sources is generally estimated from surveys, and is known very poorly. Because of uncertainty about whether these sources are used in sustainable ways and, even more importantly, because the release of products of incomplete combustion which are potent greenhouse gases are poorly characterized, the overall contribution of non-commercial energy sources to greenhouse gas emissions is only somewhat better than an educated guess at this time.
An important observation from Table 3.1 is the high AAGR in the transport sector for energy and carbon emission. AAGR is not only the greatest for the transport sector, but it has slowed only slightly since 1960 despite significant improvements in technology. Because of the increase in the number of vehicles, and the recent decline in energy efficiency gains as vehicles have become larger and more powerful, transportation now is responsible for 22% of CO2 emission from fuel use (1995). Unlike electricity, which can be produced from a variety of fuels, air and road transport is almost entirely fuelled with petroleum, except for ethanol and biodiesel used in a few countries. Biomass-derived fuels and hydrogen production from fossil fuels with carbon sequestration technology, in parallel with improved fuel efficiency conversion, are some of the few more promising alternatives for reducing significantly carbon emissions in the transport sector for the next two decades. The accelerated introduction of hybrid and fuel cell vehicles is also promising, but these gains are already being offset by increased driving, and the rapid growth of the personal vehicle market worldwide.
Oil, gas, and coal availability is still recognized to be very extensive. Fossil fuel reserves are estimated to be approximately five times the carbon content of all that have been used since the beginning of the industrial revolution. The possibility of using gas hydrates and coal bed methane as a source of natural gas has increased since the SAR.
Greenhouse gas (GHG)-reducing technologies for energy systems for all sectors of the economy can be divided into three categories energy efficiency, low or no carbon energy production, and carbon sequestration (Acosta Moreno et al., 1996; National Laboratory Directors, 1997). Even though progress will continue to be made in all categories, it is expected that energy efficiency will make a major contribution in the first decade of the 21st century. Renewable technologies are expected to begin to be significant around 2010, and pilot plants for the physical carbon sequestration from fossil fuels4 will be the last mitigation option to be adopted because of cost (National Laboratory Directors, 1997). Nevertheless, with appropriate policies, economic barriers can be minimized, opening possibilities for all the three categories of mitigation options. Considering the large number of available technologies in all categories and the still modest results obtained to date (see Table 3.1), it is possible to infer that their commercial uses are being constrained by market barriers and failures as well as a lack of adequate policies to induce the use of more costly mitigation options (see Chapters 5 and 6). This should not be interpreted as a reason to reduce R&D efforts and funding, since technological advances always help to cut costs and consequently reduce the amount and intensity of policies needed to overcome the existing economic barriers. Implementing new technological solutions could start soon by establishing policies that will encourage demand for these devices and practices. Complex technological innovations advance through a non-linear, interactive innovation process in which there is synergy between scientific research, technology development, and deployment activities (OTA, 1995a; Branscomb et al., 1997; R&D Magazine, 1997). Early technology demand can be stimulated through well-placed policy mechanisms.
In this chapter numerous technologies are discussed that are either already commercialized or that show a probable likelihood to be in the commercial market by the year 2020, along with technologies that might possibly contribute to GHG abatement by 2010. For the quantification of the abatement capacity of some of the technologies a horizon as far as 2050 must be considered since the capital stock turnover rate, especially in the energy supply sector, is very low.
A number of new technologies and practices have gained importance since the preparation of SAR, including:
Cost data are presented in this chapter for many mitigation options. They are derived from a large number of studies and are not fully comparable. However, in general, the following holds for the studies quoted in this Chapter. The specific mitigation costs related to the implementation of an option are calculated as the difference of levelized costs5 over the difference in greenhouse gas emissions (both in comparison to the situation without implementation of the option). Costs are generally calculated on a project basis (for a definition see Chapter 7, Section 7.3.1). The discount rates used in the cost calculation reflect real public sector discount rates (for a discussion of discount rates, see Chapter 7, Section 7.2.4). Generally, the discount rates in the quoted studies are in the range of 5%12% per year. It should be noted that the discount rates used here are lower than those typically used in private sector decision making. This means that options reported in this chapter to have negative net costs will not necessarily be taken up by the market. Furthermore, it should be noted that in some cases even small specific costs may form a substantial burden for companies.
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