Abstract: Fair comparison of the climate impacts from different energy sources can be made only by accounting for the emissions of all relevant greenhouse gases (GHGs) from the full energy chain (FENCH) of the energy sources. FENCH-GHG emission factors of most of the non-fossil fuel energies are lower than those of the fossil fuels that are in the range of 500-1200 g CO2/kW h(e). The improvement rates concerning their CO2-to-energy ratios of OECD countries and some developing countries are discussed, showing the low performance of the latter from 1965-1996. Detailed FENCH-GHG systems analyses are given for nuclear power, hydropower, and wind and solar power. The FENCH-GHG emission factor of nuclear power is 8.9 g CO2-equiv./kW h(e) and applies to light-water nuclear power plants. The main contributions are from milling, conversion of lower-grade ore, enrichment, construction and operation of the power plant, and reprocessing (if relevant). For hydropower an emission factor is reported of 16 g CO2-equiv./kW h(e) for the best investigated flat-area cold climate power plants. The main, biogenic, emission source is the water reservoir. The information on high-altitude alpine reservoir-type and run-of- river hydropower generation is limited. These plants could probably have emission factors in the low range of 5-10 g CO2-equiv./kW h(e). The FENCH CO2-equivalent emission factors of wind power systems are in the order of 15 g CO2-equiv./kW h(e). The main source is associated with the materials for the turbine and for its foundation. Solar PV and solar thermal power are in an intermediate range their current values are 100-200 and 50-80g CO2-equiv./kW h(e), respectively. GHG emissions are mainly from silicon, which dominates the PV market.