In the wake of climate change, social theory has been subject to a surge of new materialist and posthuman approaches that reconfigure ontology and politics beyond the modern nature/culture binary which the Anthropocene has rendered untenable. But their (re-)turn to ontological speculation brackets the socio-epistemic situatedness and productivity of the way we think nature and its relationship to society. This paper reads Niklas Luhmann’s systems theory as a posthuman perspective that can address the epistemological blind spot of materialist-ecological thought. Luhmann’s ecology aligns with the former on the posthuman framing of shaping power, the productivity of an environmental outside that remains unknown, and the call for political modesty which follows. On the other hand, Luhmann’s theory poses a critical challenge to materialist-ecological thought: the society/environment binary is here constitutively necessary, and its mapping onto a nature/culture binary functionally advantageous for subjects and social systems because it offers opportunities for complexity-reduction.