Climate change is affecting ocean temperature, acidity, currents, and primary production, causing shifts in species distributions, marine ecosystems, and ultimately fisheries. Earth system models simulate climate change impacts on physical and biogeochemical properties of future oceans under varying emissions scenarios. Coupling these simulations with an ensemble of global marine ecosystem models indicates decreasing global fish biomass with warming. However, regional projections of these impacts remain much more uncertain. Here, we employ CMIP5 and CMIP6 climate change impact projections using two Earth system models coupled with four regional and nine global marine ecosystem models in ten ocean regions to evaluate model agreement at regional scales. We find that models developed at different scales can lead to stark differences in biomass projections. On average, global models projected greater biomass declines by the end of the 21st century than regional models. For both global and regional models, greater biomass declines were projected using CMIP6 than CMIP5 simulations. Global models projected biomass declines in 86% of CMIP5 simulations for ocean regions compared to 50% for regional models in the same ocean regions. In CMIP6 simulations, all global model simulations projected biomass declines in ocean regions by 2100, while regional models projected biomass declines in 67% of the ocean region simulations. Our analysis suggests that improved understanding of the causes of differences between global and regional marine ecosystem model climate change projections is needed, alongside observational evaluation of modelled responses.

Climate change could irreversibly modify Southern Ocean ecosystems. Marine ecosystem model (MEM) ensembles can assist policy making by projecting future changes and allowing the evaluation and assessment of alternative management approaches. However, projected future changes in total consumer biomass from the Fisheries and Marine Ecosystem Model Intercomparison Project (FishMIP) global MEM ensemble highlight an uncertain future for the Southern Ocean, indicating the need for a region-specific ensemble. A large source of model uncertainty originates from the Earth system models (ESMs) used to force FishMIP models, particularly future changes to lower trophic level biomass and sea ice coverage. To build confidence in regional MEMs as ecosystem-based management tools in a changing climate that can better account for uncertainty, we propose the development of a Southern Ocean Marine Ecosystem Model Ensemble (SOMEME) contributing to the FishMIP 2.0 regional model intercomparison initiative. One of the challenges hampering progress of regional MEM ensembles is achieving the balance of global standardised inputs with regional relevance. As a first step, we design a SOMEME simulation protocol, that builds on and extends the existing FishMIP framework, in stages that include: detailed skill assessment of climate forcing variables for Southern Ocean regions, extension of fishing forcing data to include whaling, and new simulations that assess ecological links to sea-ice processes in an ensemble of candidate regional MEMs. These extensions will help advance assessments of urgently needed climate change impacts on Southern Ocean ecosystems.

Laura Kaikkonen1,2, Rebecca J Shellock3,4, Samiya Ahmed Selim5, Renis Auma Ojwala6, Beatriz S. Dias7, Shenghui Li8, Charles I. Addey9, Ignacio Gianelli10,11, Katherine M Maltby12, Sara Garcia-Morales13,14, Juliano Palacios-Abrantes15, Shan Jiang16, Marta Albo-Puigserver17, Virginia A. García Alonso18, Chelsey A. Baker19, Colleen B. Bove20, Stephanie Brodie21, Lol Iana Dahlet22,23, Jewel Das22,24, Aislinn Dunne25, Sebastian C.A. Ferse22,26, Ellen Johannesen6, Julia Jung27, Eugenia Merayo Garcia28, Denis B. Karcher29,   Sarah Mahadeo6, Lucia Millan30, Kasali Oladepo Lawal31, Ayodele Oloko32, Kelly Ortega-Cisneros33, Stephanie Otoabasi-Akpan34, Durlave Roy35, Samina Sharmin Rouf36, Szymon Smoliński37, Natasa Vaidianu38,39, Chris Whidden40, Mia Strand41National Institute of Water and Atmospheric Research, New ZealandUniversity of Helsinki, FinlandInstitute for Marine and Antarctic Studies, Hobart, Tasmania, AustraliaCentre for Marine Socioecology, University of Tasmania, AustraliaCenter for Sustainable Development, University of Liberal Arts BangladeshWorld Maritime University-Sasakawa Global Ocean Institute, Malmö, SwedenCollege of Fisheries and Ocean Sciences, University of Alaska Fairbanks, USGuangdong Ocean University, ChinaDepartment of Oceanography, University of Hawaii at Manoa, USEqualSea Lab-CRETUS. Department of Applied Economics, Universidade de Santiago de Compostela, SpainSouth American Institute for Resilience and Sustainability Studies (SARAS), UruguayGulf of Maine Research Institute, Maine, USMarine Environmental and Sciences Centre (MARE-ARNET), University of Lisbon, PortugalEcology and Biodiversity Institute (IEB), ChileInstitute for the Oceans and Fisheries, The University of British Columbia, Vancouver CanadaState Key Laboratory of Estuarine and Coastal Research, East China Normal University, Shanghai, ChinaCentro Oceanográfico de Baleares, Instituto Español de Oceanografía (IEO‑CSIC), Ecosystem Oceanography Group, Palma, SpainInstituto de Biodiversidad y Biología Experimental y Aplicada (IBBEA, CONICET-UBA)National Oceanography Centre, Marine Systems Modelling, Southampton, UKUrsinus College; Biology Department; Collegeville, United StatesEnvironment, Commonwealth Scientific and Industrial Research Organisation, Brisbane, Queensland, AustraliaLeibniz Centre for Tropical Marine Research (ZMT), GermanyInstituto de Estudos Costeiros, Universidade Federal do Pará (UFPA), Bragança, BrazilInstitute of Marine Sciences, University of Chittagong, Chattogram, BangladeshRed Sea Research Center, King Abdullah University of Science and Technology, Saudi ArabiaDepartment of Marine Ecology, Faculty of Biology and Chemistry, University of Bremen, Bremen, GermanyCobra Collective, Egham, United KingdomJoint Nature Conservation Committee, UKAustralian National Centre for the Public Awareness of Science, Australian National University, Canberra, AustraliaInstitut de Ciències del Mar - CSIC, Barcelona, SpainDepartment of Marine Science and Technology, Federal University of Technology Akure, NigeriaInstitute for the Oceans and Fisheries, The University of British Columbia,CanadaDepartment of Biological Sciences, University of Cape Town, Cape Town, South AfricaFederal University of Technology, AkureBangladesh Open UniversityBertarelli Foundation’s Marine Science Programme, Zoological Society of London, UKNational Marine Fisheries Research Institute, Gdynia, PolandFaculty of Natural and Agricultural Sciences, Ovidius University of ConstantaInterdisciplinary Center of Advanced Research on Territorial Dynamics, University of Bucharest, RomaniaFaculty of Computer Science, Dalhousie UniversityDepartment of Development Studies, Nelson Mandela University, Gqeberha, South Africa

There is an urgent need for models that can robustly detect past and project future ecosystem changes and risks to the services that they provide to people. The Fisheries and Marine Ecosystem Model Intercomparison Project (FishMIP) was established to develop model ensembles for projecting long-term impacts of climate change on fisheries and marine ecosystems while informing policy at spatio-temporal scales relevant to the Inter-Sectoral Impact Model Intercomparison Project (ISIMIP) framework. While contributing FishMIP models have improved over time, large uncertainties in projections remain, particularly in coastal and shelf seas where most of the world’s fisheries occur. Furthermore, previous FishMIP climate impact projections have mostly ignored fishing activity due to a lack of standardized historical and scenario-based human activity forcing and uneven capabilities to dynamically model fisheries across the FishMIP community. This, in addition to underrepresentation of coastal processes, has limited the ability to evaluate the FishMIP ensemble’s ability to adequately capture past states - a crucial step for building confidence in future projections. To address these issues, we have developed two parallel simulation experiments (FishMIP 2.0) on: 1) model evaluation and detection of past changes and 2) future scenarios and projections. Key advances include historical climate forcing, that captures oceanographic features not previously resolved, and standardized fishing forcing to systematically test fishing effects across models. FishMIP 2.0 is a key step towards a detection and attribution framework for marine ecosystem change at regional and global scales, and towards enhanced policy relevance through increased confidence in future ensemble projections.