Changes in temperature extremes in Russia after 1945 are examined, and their effect on power system performance is analyzed. It is indicated that the Unified Power System (UPS) of Russia and all integrated power systems (IPS) presently have a considerable amount of installed and available spare capacities. However, a quarter of the regional power systems suffer a power shortage, and three of seven integrated regional power systems of Russia (Northwest, Center, and South) feature a deficit in the power control range, which is covered by power flows from adjacent power systems (Middle Volga, Urals, and Siberia). Based on the meteorological monitoring results and power industry statistic, the observed change in the extremal climatic characteristics over the past 70 years was calculated. Its effect on the power balance and power system modes was assessed. It has been established that climatic changes that occurred in Russia and manifested themselves in an increase in the air temperature in all seasons in all regions of the country reduce the maximum load increase rate in the winter and raise it in the summer in almost all power systems, thereby contributing to an increase in the reliability of electricity supply. For the summer, a continuous increase in the power demand maxima in combination with an enhancement in the nonuniformity of the daily demand, and, as a result, a greater need for the control range mean an increase in the risk of massive power supply failures. It has been demonstrated that, against this background, a decrease in the output of generating facilities (such as thermal power plants (TPP), hydroelectric power plants (HPP), and nuclear power plants (NPP)) in hot weather and accidents at power facilities lead to the depletion of the available spare power and substantiate the fact that many consumers can be disconnected in the power systems of the South and the Center.