This article details the epistemic politics that shape the climate adaptation of sea defense in Guyana. Rethinking the material arrangements of expertise in the Anthropocene, I track the work of a group of technoscientific experts participating in the Guyana Mangrove Restoration Project (GMRP). In an attempt to redesign sea defense around mangrove ecosystems, GMRP participants recognize that climate adaptation is not solely dependent on their well‐intentioned efforts. As research objects, mangroves are not only forms of evidence but also tools that guide expert action and distinctions in day‐to‐day labor. Moreover, mangroves draw out the explicit contingencies of modeling, placing expert groups in tension with one another as each seeks to advance their own ideas for mangrove protection, management, or change. I show that this relational ontology is emblematic of climate‐adaptation policy's broader operative logics, or what I call inverse performativity. This is a process whereby an unruly world forces one expert group to seek help from others, building a new ecology of expertise to adapt to a changing climate. Impermanent and wondrous, mangroves urge us to think more creatively about vulnerability to climate change and the kinds of practices that inspire knowledge about it.