One of the reasons humans may of climbed out of the tree is climate change. The area of Africa just dried out and the forest thinned out.
Understand that a warmer world or a colder world shifts and changes climate of areas on this planet...Who's to say that the polar vortex isn't more likely to move southward because of a weaker jet stream more often? This weaker jet stream because of a "slightly" weaker temperature gradient.
No, the reason why man got out of the trees is because it is more efficient to walk bipedal.
I just find it amusing that you guys claim EVERYTHING on this damned planet is the fault of climate change. It's hilarious.
There is one facet of climate change that does contribute to evolution however, and that pertains to where on the planet you live. At the poles little to no evolution. At the equator, the same. Where evolution occurs like gangbusters is in the temperate zones where the climate changes from cold to warm to cold in endless cycles.
It is those cycles that allow the various advantages that certain creatures have to shine.