Why do changes in suns energy affect the climate on earth

The sun is a vital part of the earth, so if it changes energy levels, it will clearly have an affect on the earth. If the energy increases, it'll most likely dry out the grass and melt the snow, etc. If it decreases, the snow could freeze and change the climate.

The sun is the source of most of the energy that drives the biological and physical processes in the world around us—in oceans and on land it fuels plant growth that forms the base of the food chain, and in the atmosphere it warms air which drives our weather. The rate of energy coming from the sun changes slightly day to day. Over many millennia in the Earth-Sun orbital relationship can change the geographical distribution of the sun’s energy over the Earth’s surface. It has been suggested that changes in solar output might affect our climate—both directly, by changing the rate of solar heating of the Earth and atmosphere, and indirectly, by changing cloud forming processes. 

I’m not really sure