The impact of climate change on the efficiency of nuclear power plants and cooling reservoirs depends, to a certain extent, on the increase in the temperature of cooling reservoirs in the summer months of the year. Nuclear power plants use water throughout their lifetime in cooling systems to dissipate the waste heat generated, including system safety, cooling systems and for power generation. In this work, on the basis of the analysis of monitoring data, the correlation dependences between the temperature indicators of atmospheric air and cooling reservoirs for operating nuclear plants in the conditions of Ukraine are established. In order to obtain the efficiency of the operation of nuclear power plants depending on global climate changes, based on the analysis of the average monthly temperature indicators of the atmospheric air for the period 1881-2020, we made a climatic forecast of the atmospheric air for the territory of Ukraine and established the forecast dependence of the increase in air temperature for the period until 2160. Based on the assessment and forecasting of the influence of climatic factors on the temperature of the cooling water in the specified reservoirs and on the power of the stations, the values of the relative overall efficiency of the reactor at the NPP of Ukraine for the periods 2021-2030, 2031-2040 and 2041-2050 have been established. The obtained data, output power coefficients indicate a gradual decrease in output power in the next decades and in the Ukrainian nuclear energy sector in terms of operating nuclear power plants in the conditions of forecast values of global warming and cooling water temperature. They testify that climate change and global warming are a risk of emergency situations at nuclear power facilities, which requires making strategic decisions regarding adaptations of reactor operation in conditions of global climate change.