Climate change in the global ocean

Quantifying past and future trends of marine ecosystems caused by global change is critical to inform ongoing climate change and biodiversity assessments, and to guide feasible pathways towards achieving key policy objectives globally^[1]. To predict the future of marine biodiversity and ecosystem services there is a need to adopt an integrated view of the ocean as a social-ecological system, encompassing the dynamics of commercial and non-commercial species and their interactions, the dynamics of resource users and their interactions, and how those are affected by changing environmental conditions and management interventions^[2]. This understanding can only be attained with studies at multiple scales, where global studies are essential as environmental changes and socio-economic interactions are often coupled and cascading impacts of ecological disturbances affect human use of ecosystem services across vast distances through ocean currents, species movements and fishing fleet mobility^{[3] [4]}.

The last decades have witnessed extensive development of modeling techniques at global scales both in terrestrial and marine domains^[5][6]. Rapid development of atmospheric-ocean circulation models, including biogeochemical processes in Earth System Models (ESM), has improved the scientific capability to project the climate system, which in turn has helped inform the United Nation (UN) Intergovernmental Panel on Climate Change (IPCC, (Shukla et al., 2019). Ecosystem models have also shown a dramatic increase in their development, especially in the marine realm^[7].

These Marine Ecosystem Models (MEMs) are used to project changes in marine ecosystems at global scales, including the impacts of fishing and other human activities and stressors. They are now being synthesized into ensemble model projections, contributing towards extending the scientific capability to project what the future oceans may look like, how different scenarios may play out, and what the range of uncertainty is for different components and processes^{[8] [9]}. This is important both for the IPCC but also for the IPBES international platforms^[10].

Figure 1. Schematic structure of EcoOcean v2 modeling complex (reproduced from Coll et al., 2020)

The EcoOcean model^{[11] [12]} is a global modeling complex with a tropho-dynamic core that represents one of these initiatives with a global scope. EcoOcean is a spatially and temporally explicit mechanistic marine ecosystem model that unifies the consideration of spatial-temporal food-web dynamics ranging from primary producers to top predators with the impacts of environmental change and worldwide fisheries and cumulative impacts of anthropogenic activities. EcoOcean was built upon a heavily modified version of Ecospace, where EwE calculations were expanded or replaced to represent spatial heterogeneity in fishing and the behavior, growth and movement of functional groups across the worlds’ oceans (Figure 1). Applications of EcoOcean v2 include a global assessment of the impacts of climate change under different projected trajectories (Figure 2) and climate change and fisheries (Table 1), the effects of MPAs and fisheries management strategies, the assessment of uncertainties associated with climate change drivers’ responses and the analysis of global teleconnections^{[13] [14] [15]}

Figure 2. Results of EcoOcean v2 regarding climate impacts under two contrasting scenarios of climate change (RCP 2.6 and 8.5) and two Earth System Models (GFDL and IPSL) —Relative temporal change of Total Consumers Biomass (%) by sub-regional oceans: (A) GFDL RCP2.6; (B) GFDL RCP8.5, (C) IPSL RCP2.6, and (D) IPSL RCP8.5 (reproduced from Coll et al., 2020).

Table 1 – Results of EcoOcean v2 regarding climate impacts in comparison with climate and fishing impacts —Temporal Change (%) of biomass by functional groups (reproduced from Coll et al., 2020)