In this article, we study third-year university students' reasoning about three controversial socio-scientific issues from the viewpoint of education for sustainable development: local issues (the reintroduction of bears in the Pyrenees in France, wolves in the Mercantour) and a global one (global warming). We used the theoretical frameworks of social representations and of socio-scientific reasoning. Students' reasoning varies according to the issues, in particular because of their emotional proximity with the issues and their socio-cultural origin. About this kind of issues, it seems pertinent to integrate into the operations of socio-scientific reasoning not only the consideration of values, but also the analysis of the modes of governance and the place given to politics.