Achieving global climate goals and securing future food supplies poses significant challenges, especially if efforts are limited to land-based solutions. Given that the ocean covers over 70% of the Earth’s surface and plays a critical role in CO2 sequestration, exploring ocean-based climate mitigation strategies will be essential. One promising approach is Ocean Alkalinity Enhancement (OAE), a form of marine geoengineering aimed at accelerating the ocean’s natural carbon sink, reducing atmospheric CO2 levels, and mitigating ocean acidification. However, the implications of OAE for global fisheries, which are vital for food security and livelihoods worldwide, remain underexplored. This study develops and analyzes future scenarios for global fisheries under different socioeconomic and climate trajectories, utilizing the Shared Socioeconomic Pathways (SSPs) and Representative Concentration Pathways (RCPs) framework. Specifically, we focus on three combined pathways: SSP1-2.6, SSP3-7.0, and SSP5-8.5, to explore the potential impacts of OAE implementation. Through an integrated narrative approach, we (semi-)quantify changes in key bio-economic parameters such as technological progress, fishing costs, fisheries management, marine aquaculture, and carrying capacity, providing an explorative assessment of how OAE could influence these under varying global conditions. With this approach, we contribute to the development of sector-specific and long-term interdisciplinary models that are crucial for future policy and management strategies aimed at climate change mitigation and the sustainable use of marine ecosystems. Our framework aligns with global scenarios that are being applied internationally.

The Fisheries and Marine Ecosystems Model Intercomparison Project (FishMIP) has dedicated a decade to unravelling the future impacts of climate change on marine animal biomass. FishMIP is now preparing a new simulation protocol to assess the combined effects of both climate and socio-economic changes on marine fisheries and ecosystems. This protocol will be based on the Ocean System Pathways (OSPs), a new set of socio-economic scenarios derived from the Shared Socioeconomic Pathways (SSPs) widely used by the Intergovernmental Panel on Climate Change (IPCC). The OSPs extend the SSPs to the economic, governance, management and socio-cultural contexts of large pelagic, small pelagic, benthic-demersal and emerging fisheries, as well as mariculture. Comprising qualitative storylines, quantitative model driver pathways and a “plug-in-model” framework, the OSPs will enable a heterogeneous suite of ecosystem models to simulate fisheries dynamics in a standardised way. This paper introduces this OSP framework and the simulation protocol that FishMIP will implement to explore future ocean social-ecological systems holistically, with a focus on critical issues such as climate justice, global food security, equitable fisheries, aquaculture development, fisheries management, and biodiversity conservation. Ultimately, the OSP framework is tailored to contribute to the synthesis work of the IPCC. It also aims to inform ongoing policy processes within the United Nations Food and Agriculture Organisation (FAO). Finally, it seeks to support the synthesis work of the Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services (IPBES), with a particular focus on studying pathways relevant for the United Nations Convention on Biological Diversity (CBD).