Also, the increase in world population isn't going to go on forever. Birth rates are decreasing in most countries - including third world countries. In fact, the population of many states in India is increasing not because of birth rates but due to increasing life expectancy. I can't find a cite now, but I remember an article which expects world population to stabilize at something less than 10B. If even that number seems worrying, remember that vast swaths of land in Central Asia, Siberia, Canada, Alaska, Australia and Antartica are virtually uninhabited: we don't even need to go the moon or Mars or something to find space for humans.
We do need to get our act together but our real problems are effective policy-making and governance. Not finding endless sources of energy.