Rethinking ocean alkalinity enhancement

Abstract

Ocean alkalinity enhancement (OAE) aims to increase the capacity of seawater to durably store anthropogenic carbon dioxide (CO2). OAE has been portrayed as a top–down coordinated geoengineering approach that could potentially remove gigatonnes of CO2 per year from the atmosphere. In this Perspective, we argue that OAE should instead be considered as a flexible tool for localized CO2 management. Integrating small-scale OAE into diverse local contexts has the potential to deliver achievable mitigation goals defined by individual governments and communities. The diversity of OAE pathways favours implementation of an OAE portfolio across heterogeneous coastal environments. Upscaling could be achieved through widespread bottom–up adoption of diverse OAE pathways, but only if these are environmentally responsible, demonstrably carbon-negative, and receive public trust. This practical vision is consistent with early real-world OAE deployments. However, adopting it requires substantial adjustments in environmental and geochemical assessments, CO2 removal verification, and governance. There is a need to move away from a globally uniform perspective and towards locally designed and context-relevant research, policy and practice. Ocean alkalinity enhancement (OAE) is often thought of as a global-scale geoengineering approach to mitigate climate change. This Perspective explores the environmental effects, geochemical constraints, verification and governance of OAE and argues for local-scale, context-led evaluation.