Saturn's equatorial plane has an inclination of 26.75° to the plane of its orbit. Therefore, its atmosphere is characterized by seasonal changes. Because of the eccentricity of 0.056 orbit, the southern hemisphere receives 25% more energy from the sun than the northern one, because the aphelion of Saturn occurs in the summer in the northern hemisphere, and perihelion in the summer in the southern. At the moments of equinox, the planet is at an average distance to the Sun. We digitized up to 200 images of Saturn obtained by different observers at the equinoxes of 1966, 1980, 1995, 2010, and prepared brightness distributions along several latitudinal belts and along the central meridian in the spectral range of 300...890 nm. Using the available photometric and polarimetric data, we calculated the intensities of radiation diffusely reflected from the atmosphere within the framework of a two-layer model. In it, the upper layer is an optically thin gas layer, the lower one is a semi-infinite gas-aerosol layer. The atmospheric parameters were obtained by comparing the observational data with the calculated values. Analysis of the distributions of methane and ultraviolet (UV) absorption over the disk for the period 1964–2020. showed seasonal variations in the levels of formation of visible clouds and above-cloud fog. Meridional course of absorptions at equinoxes in 1966 and 1995 is the opposite of the course of changes obtained from observations at the 1980 equinox. But the expected difference in the course of absorption between the hemispheres of Saturn in 2010, and as that obtained in 1980, did not occur. Although all the orbital and physical characteristics on Saturn are repeated at the moments of the four equinoxes, the response of the atmosphere to them was different. The available seasonal models of Saturn's climate change are in good agreement with seasonal changes in methane and UV absorption in its atmosphere at the equinoxes of 1966, 1980, 1995. But the data from observations of the planet's hemispheres at the 2010 equinox showed a significantly different result. A study of observations from Voyagers and Cassini showed that at tropopause levels, the tropical regions of Saturn's atmosphere warmed by more than 10 K in one year (from 1980 to 2010). Such warming in the tropopause has significantly altered atmospheric stratification, stability, and influenced the large-scale dynamics of the upper troposphere. At the minimum of solar activity in 2010, atmospheric convection also significantly decreased.