Briefly describe three of the theories scientists have proposed to explain natural climate changes.

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)

Its in the national history museum and you can't se the original because its locked away in a vault