Sun is not exactly constant, as it experiences changes in radiation levels and appearance. The measured solar cycles have an average of approximately eleven years and could affect us in different ways.
The cycle was discovered by a German astronomer called Heinrich Schwabe in 1843, and since then it's observed carefully with all available technology.
It's believed that all solar activity is being modulated by Sun's internal magnetic fields, causing a difference in the number of sunspots, coronal mass ejections and changes in solar irradiance. There is a lot of individuals searching with their telescopes for ejections and sunspots, creating awesome images.
Climate could be also related with this theoretical solar cycle, and for sure coronal mass ejections can be even dangerous as it's a source for high energy radiation (solar wind) traveling toward Earth producing geomagnetic storms.
But not all solar wind cause problems since sometimes it's the main reason of another surprising phenomena happening in the atmosphere: the aurora borealis.