Thus, it must be clear to everybody that once we have made this ethical choice to strive for sustainablity, once we decided to make sustainable development the underlying principle for our economic and social activities, then a successful quest requires solid scientific input: living on a dynamic, evolving, complex planet, a planet, as pointed out by Lovelock in his Gaja hypothesis, in a homestatic equilibrium, with a physiology comparable in its complexity to that of a human body, living on a planet we share with a rich biosphere with many biological components and ecological conditions contributing to the state and dynamics of the planet, it is extremely challenging not to compromise the ability of fellow people and future generations to meet their needs.