There is no next. In fifty years the ecology will collapse and civilization will either reboot or die.
By most accounts we are already in the midst of the single largest extinction event in the history of the planet. Within twenty years there won't be enough fish to sustain commercial fishing and already fish farms are taking over the business. Within fifty years its projected most land wild land animals larger then a dog will be extinct. No more elephants, lions, tigers, and bears (oh my!) except in zoos which are going crazy collecting as many as possible right now. In fact, there are even concerted efforts to store embryos and plant seeds.
Then there's the water problem. Forget oil, within fifty years most of the world's largest aquifers will run dry. Already emergency food supplies are dropping thanks in part to people converting more food into fuel. People are already struggling to capture all the rainwater they can, but its not enough to make up for the lost aquifers. We can clean dirty water and use less, but all that costs money and half the world lives on $2.oo a day and it is these poor people who have the worst population problems.