Universal birth control would certainly be a very good start, but even if the world's population stabilised tomorrow, we'd still be in the shit thanks to the established industrialisation of the developed world and the very rapid development of industry in the developing world.
To put it another way: as far as I understand it (and if I'm talking arse here, please feel free to tell me so!) we're already passed the point of inflection in the world population curve, so that while the population is obviously still increasing, the rate at which it's increasing is itself slowing down (so that, if P = total world population, then d^2 P/d t^2 is negative, if you will). In particular, China's population has more or less stabilised, thanks to the (in)famously effective One Child policy. Most of the world's population growth is occurring in Africa and the Middle East, areas that for the most part have yet to undergo large-scale industrialisation.