[DOES THE FOLLOWING BLOCK OF TEXT BELONG SOMEWHERE OR HAS IT BEEN DELETED?] 39 After CO2, methane (CH) most likely accounts for the largest anthropogenie contribution (about 18%) to greenhouse warming, although there is still considerable uncertainty about methane emissions." Major sources of anthropogenic methane are: losses from the production and distribution of natural gas, releases from coal mining, from ruminant animals, from paddy rice production, and from the release of land fields. For natural gas in distribution most of the losses occur from leaks in the pipe work. The remaining losses stem from routine maintenance, pressure release valves and non efficient end-use applications. In production losses are due to leakage at wellheads and gas treatment plants, venting and incomplete flaring operations and exploration and drilling activities. Data available for 1984 on the fraction of vented and incompletely flared gas released during production of natural gas reveal wide discrepancies between the various regions: 1% in North America, 2% in Europe and CIS, 11% in Asia and Australia, 18% in Central and South America, 40% in Africa and 61% in the Middle East (!) (Fung et al., 1991). The information currently available about methane leakage in distribution is also rather seanty. According to some authors, methane releases from gas production and transportation in the CIS and Eastern Europe may well be by far the largest sources of emissions, accounting for perhaps 50% of total global emissions (Ebert et al., 1993). Others, however, suggest that much of these losses may be explained by "errors" in accounting. For example, in Bangladesh in the 1980s a rapidly increasing share of total gas was unaccounted for, that had risen from about 1% in 1981 to 10% by 1990. A report on these losses identified as eauses of the increasing loss besides leakage: inaccurate meter reading, excessive use in unmetered connections and unauthorized gas connections." 40 According to Van Amstel et al. (1993), currently available techniques allow for a 70% reduction of methane emissions from coal mining (particularly gassy mines). Future techniques may increase the figure up to 90%. For oil and natural gas production many techniques are available as well. Rubin et al. (1992) estimate the costs: of eliminating US paddy rice production at about $0.5/tCO2; and of reducing US ruminant animal production by 25% at $2/tCO2 (for a crude overview of the technological options for reducing methane emissions from different source sectors and their capital needs, see also Van Amstel et al., 1993, p. 28). There is a lack of similar cost information on, for instance, reducing methane from rice production or from ruminant animals in developing countries. 39. Known emissions of methane are in the range of 331-850 Tg/yr, while the total size of the known sinks ranges between 463 and 602 Tg/yr (Watson et al., 1992). 40. Task Force Report on Energy, 1991, p. 40. 8 ESTIMATING THE COSTS OF MITIGATING GREENHOUSE GASES Convening Author: J. C. Hourcade Principal Lead Authors: Lead Authors: W. Chandler, O. Davidson, J. Edmonds, D. Finon, M. Grubb, K. Halsnaes, K. Hogan, M. Jaccard, F. Krause, E. La Rovere, E. D. Montgomery, P. Nastari, A. Pegov, K. Richards, L. Schrattenholzer, D. Siniscalco, P.R. Shukla, Y. Sokona, P. Sturm, A. Tudini SECOND EDITED DRAFT 1.2.1 Gross Costs, Net costs, and the Overall Cost-Benefit Balance of 1.3 Key Factors Affecting the Magnitude of Costs: Costs as a Function of 2. Patterns of Development and Technological Change 2.1. Links Between Development Patterns, Technical Change, and Mitigation 2.1.1 The Importance of the Socioeconomic Assumptions Underlying 2.1.2 Current and Future Socioeconomic Development Patterns 2.2 Modeling Development Paths and Mitigation Costs.... 6 7 .. 15 15 15 18 2.2.1 Prediction and Simulation: The Need for Multiple Baselines .... 22 2.3 Multiple Baselines, Uncertainty and Long-Term Mitigation Costs 2.3.2. The Meaning of the Baseline 3. Differences among Models and their Results 25 25 .. 26 3.1 General Methodological Considerations 3.2. Critical dimensions of a typology of existing models 29 .... 3.3 The Top-Down Down versus Bottom-Up Modelling Controversy: Some 36 3.4 Beyond Energy: Carbon Sinks and Nonenergy Greenhouse Gas Figure 8.1 Energy Technology Cost Curve List of Figures and Tables Relationship Between Economic Activity and Emission Reduction Table 8.1 Key Structural Characteristics in Energy/Economy Models 31 Key Structural Distinctions Between Bottom-Up and Top-Down Models 32 35 ... 41 |