ABSTRACT Ecosystem changes are happening with surprising speed and on much shorter‐than‐projected time scales. This essay explores the complexities of such abrupt environmental shifts, how scientists conceptualize a runaway nature, and how uncertainty poses a problem of projection and action. Its ethnographic material engages contexts where rapidly faltering projections and policies interface in unsettled ways with the realities of emergency response, especially to wildfires. Attuned to the political and existential hazards at work in a science of critical transitions, the essay argues for the importance of a distinct kind of intellectual and ethical labor, horizoning work, amid physical worlds on edge.