This paper analyzes the theoretical and pragmatic implications, for international relations and world politics, of the new holistic approach to climate change articulated by Pope Francis in the Encyclical Laudato si’, particularly through the notion “integral ecology”. Far for being just a new chapter in the unfolding process of the “greening” of religions, the document raises in radical terms the issue of the sustainability of the present world system. I contend that the perspective of the Encyclical calls for a radical transformation of international relations, since it puts emphasis on the deep implications of environmental issues on the entire spectrum of security, development, economic and ethical challenges of contemporary world politics. Against this backdrop, I connect the main tenets of the Encyclical to the environmental turn in International Relations Theory and to the new epistemological challenges related to paradigm shift induced by the new planetary condition of the Anthropocene and the questions arising for a justice encompassing the humanity-earth system. Practicing sustainable international relations means exiting the logic of power or hegemony, operationalizing the concept of care.