I will answer this question as when the first humans came about. We are homo sapiens, however before us there were many other homo type humans that evolved from an ancestor of chimpanzees or bonobos. Those other homo species of humans eventually became extinct. The first homo sapiens evolved in africa after some huge droughts or dry periods. The first humans lived in trees, and once the drought happened they moved to living on land and moved across the African continent. So in a way climate change forced the first humans to evolve.