[@Kho]

Civilizations would be constrained to a few very hospitable zones, which would foster more interactions. I see that as a plus. However half the planet is rendered mostly unusable, which sort of sucks. 

I suppose there could be civilization underground or something in the inhospitable areas, though. Yeah, I think I'll do slightly extreme seasons because that sort of drama is what Zephyrion digs.

Edit: Forgot to mention that Zephyrion's air elementals will control the weather, so praying to your local rain spirit might allow you to survive :lol