A new study co-authored by Stanford researcher Mark Z. Jacobson and UC-Davis researcher Mark A. Delucchi analyzing what is needed to convert the world's energy supplies to clean and sustainable sources says that it can be done with today's technology at costs roughly comparable to conventional energy, and converting will be a massive undertaking on the scale of the moon landings. In addition, what is needed most is the societal and political will to make it happen. More information is here.