Historical fact, empires crumble during grand solar minimum global cooling events. So yeah an ice age would play into geopolitics. I live in Canada, southern Ontario near Toronto so global cooling is more of a concern to me than say someone in Mexico.
It isn't just long cold winters that are a concern, already there is a huge increase in highly energetic storm events with lots of lightning and large hail smashing everything in its way. Kansas just had its summer wheat decimated by a hail storm, hail is destroying crops worldwide. There is the increase in galactic and solar cosmic rays as well as the potential for a repeat of a Carrington like event that some scientists say we are overdue for.

As for overpopulation in the third world and fundamentalist Islam, well the latter is in direct response to US foreign policies and the former can be resolved with education. Improve education and quality of life and birth rates drop.

As for the future is religious, I'd say you're close but not right on. The future is ideologiousity-I think I created a new word-it means the religiosity of ideology whether it be political, economical or whatever. it is ideology that is causing the great divide in humanity and religion is just a small part of it. And more important it is the self-identifying with ideology that is the big problem. From there it is just a hop skip and a jump to total abdication of your sovereign human self and once that is done you are psychopathic enough for committing heinous acts against your human brothers and sisters.