This article aims to answer the following question: in which ways may catastrophism in ecological thought lead to act in order to preserve Earth’s habitable conditions as best as possible? In this perspective, the catastrophist thoughts of Hans Jonas, Jean-Pierre Dupuy, Pierre-Henri Castel and the French “collapsologues” are analysed, with those of Günther Anders and Simone Weil in the background. To answer this question, we must consider the temporality which these thinkers posit as they envision disaster (is it something to come, or is it already under way?) and the ontological inscription of the disaster in this temporality (is it inevitable or can it be avoided?). The conclusion is as follows: the perspective of disaster is indeed mobilising, for those who recognise a duty to act, when disaster is seen as unavoidable and already happening, implicitly leading to an inevitable end whose concrete contours remain uncertain, namely the disappearing of life or the overcoming of the determining factor of the disaster, i.e. Technique.