Where did you get the number 48 billion? That is way too high to be real, evolutionarily people would stop breeding long before that point. Who would want to bring a child into a world with no food or air? This is starting to become evident already IMO. Birth rates will fall until an equilibrium is reached. All animals do this, if there is no food around then breeding takes a back seat to survival. If the food supply is plentiful then population numbers increase. Just my opinion of course. :)
Thanks for the comment! I wrote this a couple years back when I wasn't as thorough with my resources so I agree :/
Unfortunately, correct birth control is still an issue in developing countries (as well as certain religions) so there is still the potential for increase in my opinion, and enough to make an impact.
Humans have seen to it that even as natural resources deplete we find new ways to maintain sustenance such as chemical laden processed foods. I still see, even after years of writing this a while back that there are great changes that need to be made. Granted to effects are probably still drastic.
http://grist.org/climate-energy/global-warming-is-now-in-overdrive-we-just-hit-a-terrible-climate-milestone/
This above article was more recent and is a good indication of the state of Global Warming at this point.