In the next fifty years, a large portion of humanity will reach a turning point. A significant portion of humanity is dependent on petroleum for energy, manufacturing and mechanized farming. I cannot stress the following enough, but there are people out there who still don't get it: OIL IS A FINITE RESOURCE. Eventually, there will no longer be any left. Between then and now, there will be a very rocky stretch of time centered around peak oil. If nothing is done to ameliorate the effects of peak oil and eventually, no oil, many people will die. If things are done, things still will not continue as usual.
If nothing is done, oil prices will be so high as to be unaffordable. Nobody will be able to get oil and oil based products for fuel, agriculture, or pharmaceuticals. The power will go out for good when utility companies cannot afford fuel for the plants. When mechanized farming grinds to a halt, food prices will soar, and the oil shortage will make moving what little can be grown an impossibility. Mass starvation will result. With poor nutrition, no power and poor to nonexistent sanitation, disease will run rampant. Diseases which are confined to the third world, rare, or only dangerous to children and the elderly will kill millions. People won't take this lying down, either. Not all deaths will be by starvation or disease. Cities will empty, and suburbs will become untenable. Society will descend to tribal levels.
On the other hand, alleviating or avoiding the effects of the end of oil would mean equally drastic changes, albeit a bit more subtle. Investment in new or underutilized technologies such as algae biofuels and breeder-cycle reactors will be necessary to avoid a total collapse of civilization. Eventually, humanity will be driven off of Earth for other resources, such as rare earth metals. Space will open up like never before. Humanity will become a species not bound to one globe.
I am 19. By the time I turn 70, humanity will have changed significantly. When I am seventy, I will either be able to retire on the moon, or I will be telling stories to children of the tribe. It could honestly go either way.