Movement of continents over time changed the location of land and sea, this affects the global patterns. Volcanic activity aerosoles and ash are let into the atmosphere and stay there for years and make the temperature lower. Solar energy lets out sunspots which are dark, cooler regions on the surface of the sun.
I can give you one: One of the theories (in which i mostly believe in) is the one when every period of time, the climate changes. Now, we are in the warmth period, but after this period, there will be a cooler climate, and keeps repeating every while (think about the ice age)
