『Abstract
　This articles presents the environmental impacts of electricity generation systems, based on life-cycle assessments (LCAs). These assessments normally include impacts from extraction, processing and transportation of fuels, building of power plants and generation of electricity.
　The LCAs show that the following options have an excellent performance: hydropower (run-of-river and with reservoir), nuclear energy and windpower.
　Hydropower with reservoir does have high land requirements, but in spite of this, it is possible to conclude that it has the highest performance, if we consider 2 factors not always included in LCAs: firstly, reservoirs can provide secondary benefits such as irrigation or flood control; and secondary, hydropower has a jigh operating flexibility that can improve the reliability of electricity supply.

Keywords: Electricity; Life-cycle; Environment; Impact』

1. Methodology
　1.1. Potential uses of life-cycle assessment
　1.2. The exceptional case of hydropower
　1.3. Main atmospheric issues covered by LCAs
　1.4. Reliability of generation systems, a criteria for rigorous comparisons
　1.5. Main types of electricity generation systems
2. Results of life-cycle assessments
　2.1. Greenhouse gas emissions
　　2.1.1. Environmental issues
　　2.1.2. Understanding the studies on greenhouse gas emissions
　　2.1.3. Main findings concerning greenhouse gas emissions
　　2.1.4. Future performance of energy systems concerning greenhouse gas emissions
　2.2. Acid precipitation
　　2.2.1. Environmental issues
　　2.2.2. Understanding the studies on SO2 emissions
　　2.2.3. Understanding the studies on NOx emissions
　　2.2.4. Main findings concerning acid precipitation
　　2.2.5. Future performance of energy systems concerning acid precipitation
　2.3. Land requirements
　　2.3.1. Environmental issues
　　2.3.2. Understanding the studies on land requirements
　　2.3.3. Main findings concerning land requirements
　　2.3.4. Future performance of energy systems concerning land requirements
　2.4. Energy payback ratio

『2.4.1. Definition
For each power generation system, the “energy payback” is the ratio of energy produced during its normal life span, divided by the energy required to build, maintain and fuel the generation equipment.』

　　2.4.2. Environmental issues
　　2.4.3. Understanding the studies on energy payback
　　2.4.4. Main findings concerning “energy payback ratios”
　　2.4.5. Future performance of energy systems concerning the payback ratio
　2.5. Other atmospheric emissions
　　2.5.1. Health issues
　　2.5.2. Comparing mercury contamination
　2.6. Conclusion
References

Fig. 5. 〔Gagnon,L., Belanger（最初のeの頭に´）,C. and Uchiyama,Y.(2002): Life-cycle assessment of electricity generation options: The status of research in year 2001. Energy Policy, 30, 1267-1278.から〕