This text brings together two ideas, those of Hannah Arendt’s republicanism and Alexander von Humboldt’s cosmopolitanism. Both ways of thinking are seen as alternatives to a republican-biocentric perspective to the current problematic areas of the political and ecological crises. Arendt’s critique of the modern natural sciences and the associated alienation from the earth, which still characterizes the current relationship to nature today, will be presented first. This critique is closely related to Arendt’s thesis of world loss, i.e., the loss of the interpersonal pluralistic sphere. As an alternative to both forms of loss, Arendt develops the concept of an independent sphere of the political based on inter-personality, harmony with nature, and dialogical and consensual politics. While Arendt approaches nature from Kant’s definition of self- and world-relationship and from her own definition of sustainable politics, Humboldt goes the opposite way, that is, from respecting nature as an independent organism to a republican understanding of politics that, like Arendt, rejects the exploitation of humans as well as nature. Arendt and Humboldt both belong to the tradition of the Enlightenment that (in addition to phenomenology, self-reflection, the values of human dignity and human rights, and the unity of understanding and feeling) also includes a cosmopolitanism and freedom of movement for acting and judging citizens.