The United States is about to become the world's largest producer of oil and gas. Quite remarkable for a country that only a few years ago was the world's largest importer of gas. It's a turnaround made possible by shale and it comes at a time of rapidly increasing demand from China, India and the Middle East. Peter Voser is the boss of Royal Dutch Shell one of the biggest energy companies in the world. With economies so thirsty for power, producers are being driven to new frontiers but at what cost?