. >> but a more sinister threat, catastrophic climate change, caused shellen burger to reconsider. >> the thing that snaps out of it is frying to figure out how dough you power a world of 7 billion people, while at dealing with climate change. with global concentrations of carbon dioxide nearing a point of no return, he doesn't believe renewables are up to the task. >> you have to look for ways to produce large quantities of energy, in smaller amounts of space. with a smaller footprint that's where i came back to nuclear, begrudgingly at first a few years ago. >> shellen bergser just one of a small but influential group of former nuclear opponents, climate scientists and innovator whose are coming out in favor of nuclear energy. how big a counter movement would you say this is. >> calling on them to support the next generation. president obama is certainly pronuclear, i get emails every week for people that are excited for an environmental vision that recognize it is need for a serious advance technology. >> how much he says the industry has learned from disaster. >> nuclear power pla