Efforts to mitigate climate change increasingly hinge on the potential large-scale deployment of geological CO2 storage. Central to this ‘carbon management’ strategy is the use of subterranean pore space for permanent sequestration. Rather than characterizing it as a neutral void or sub terra nullius awaiting productive use from climate techno-fixes, this article examines pore space as a site of ontological and material contestation, entangled with logics and infrastructures of capitalist accumulation and colonial exploitation. We first highlight how contemporary efforts to secure pore space extend longstanding practices of enclosure and extraction, deepening colonial relations, and environmental injustice under the guise of meeting urgent climate mitigation targets. Then, we show how pore space can resist full incorporation into colonial and capitalist frameworks: how its uncertain ownership regimes and unpredictable geologies create ‘fractures’ in extractivist projects. Finally, we explore pathways toward an otherwise pore space, drawing on marginalized cosmologies of the underground, geohumanities, negative commons, and community wealth-building literatures. Rather than treating pore space as an empty container for carbon, it can be reimagined as a site of relational practice and cosmological plurality. In doing so, we argue for expanding the study of pore space beyond geology and engineering to include geographers, anthropologists, and critical social scientists, in pursuit of a form of climate governance that foregrounds repair and possibility in the subterranean.