The results of a combined analysis of long-term variations of radiation budget elements, global cloudiness, intensity of galactic cosmic rays, near-surface air temperature, and characteristics of solar activity are presented. Satellite and ground-based data on variations of cloudiness and solar irradiance are summarized. Most data indicate that total cloudiness increases, on average, for the last century or, at least, last decades. The energy budget of the Earth's climatic system is calculated, and changes in the heat content of the World Ocean and the atmosphere for the last 50 years are estimated. According to the estimates, only a minor part (~ 0.1%) of the incident energy is spent for changing the heat content of the atmosphere and the ocean. Possible effects of changes in the solar constant on the energy budget of the atmosphere are discussed. The analysis of experimental data shows that, on the one hand, the radiative flux coming to the Earth decreases and, on the other hand, the heat content of the World Ocean, land, and atmosphere obviously increases. This suggests that the most significant factors for the Earth's energy budget are variations of the outgoing longwave radiation, rather than variations of the net energy flux coming to the Earth. Possible mechanisms of the sun-climate relations, which can play an important role on both short and long time intervals, are discussed. The roles of cosmic rays and the electric field of the atmosphere, which, on the one hand, are subject to solar variations and, on the other hand, can influence considerably the radiation budget of the atmosphere by affecting the atmospheric distribution of cloud condensation nuclei, phase state of water in the atmosphere and cloud cover, are considered.