Estimation of average temperature of Earth's surface: mathematical model of thermo-balance of Earth’s heat fluxes

Mathematical model of thermo-balance of Earth’s heat fluxes is suggested for such an estimation. Using well-known data (albedo of the Earth’s surface, constant of the heat radiation from the Sun per square meter of Earth’s outer atmosphere surface, etc.), we could conclude that the process of heating only by the Solar activity is not sufficient to obtain the real meaning of the temperature of Earth’s surface. Estimation yields the average temperature about -50 degrees below zero (Celcius scale) in this case. It means that there exist other sources of heating of Earth; we suppose such sources should be the inner sources of heating of Earth itself.