Although Japan has been a model of energy diversification for national security reasons, rising concern about environmental degradation may lead to the re-evaluation of these policies. The technology for reducing sulphur dioxide (SO2) and nitrogen oxide (NO(x)) emissions has been developed, but there is no technological method of eliminating carbon dioxide (CO2) emissions from fossil fuels at present. These can only be reduced by replacing part of thermal power generation with other energy sources or enhancing the thermal efficiency of power plants. The paper examines the power generation mix as a strategy for reducing emissions from thermal power plants and indicates the effect of thermal efficiency on CO2 emissions. In addition, emission levels resulting from the government plan and the alternative emission abatement power generation mix plan are compared. A multi-objective programming model is used to estimate the emission abatement power generation mix. The results show that an emission abatement strategy in conjunction with increased thermal efficiency is significantly more effective at reducing CO2 emissions than the present government plan.