Projections of climate change impacts on marine ecosystems have revealed long-term declines in global marine animal biomass and unevenly distributed impacts on fisheries. Here we apply an enhanced suite of global marine ecosystem models from the Fisheries and Marine Ecosystem Model Intercomparison Project (Fish-MIP), forced by new-generation Earth system model outputs from Phase 6 of the Coupled Model Intercomparison Project (CMIP6), to provide insights into how projected climate change will affect future ocean ecosystems. Compared with the previous generation CMIP5-forced Fish-MIP ensemble, the new ensemble ecosystem simulations show a greater decline in mean global ocean animal biomass under both strong-mitigation and high-emissions scenarios due to elevated warming, despite greater uncertainty in net primary production in the high-emissions scenario. Regional shifts in the direction of biomass changes highlight the continued and urgent need to reduce uncertainty in the projected responses of marine ecosystems to climate change to help support adaptation planning.

The ocean economy is experiencing rapid growth that will provide benefits but will also pose environmental and social risks. With limited space and degraded resources in coastal areas, offshore waters will be a particular focus of Blue Economy expansion over the next decade. When emerging and established economic sectors expand in offshore waters (within national Exclusive Economic Zones), different potential Blue Economy opportunities and challenges will arise. Following a series of interdisciplinary workshops, we imagine two technically possible futures for the offshore Blue Economy and we identify the actions required to achieve the more sustainable outcome. Under a business as usual scenario the focus will remain on economic growth, the commodification of nature, the dominance of private over public and cultural interests, and prioritisation of the interests of current over future generations. A more sustainable scenario would meet multiple UN Sustainable Development Goals and ensure inclusive economic developments, environmental sustainability, and fair and equitable access to resources and technologies across users, nations, and generations. Challenges to this more sustainable future are a lack of infrastructure and technology to support emerging offshore sectors, limited understanding of environmental impacts, inequitable outcomes, and a lack of planning and governmental oversight. Addressing these challenges will require a shift in societal values, a more balanced allocation of funding to offshore activities, transparency in information sharing between industries and across nations, and adjustment of international legal and institutional mechanisms. The sustainable and equitable offshore Blue Economy we envisage is achievable and provides a unique opportunity to build global capacity and partnership.