Overview: How much energy can be obtained from so-called "clean sources", i.e. those that do not generate carbon dioxide, the infamous CO2, responsible for the greenhouse effect? It is the theme of the new appointment with "Preparing for the future", the Rai Cultura series created and written by Piero Angela and dedicated to the new generations. Piero Angela, together with a team of experts, analyzes the advantages, but also the limits, of "clean" resources and the role of so-called energy cannibalism.