Climate Change Projections for the Southwest Pacific Ocean Using Coupled Model Intercomparison Project (CMIP) Phase 5 and 6 Models: Implications for Physics, Biogeochemistry, Ecosystems, and Fisheries

This article analyses future projections of ocean properties for a region of the south‐west Pacific Ocean encompassing the New Zealand Exclusive Economic Zone under different climate change emission scenarios. Projections are updated and expanded from previous assessments using a “best” ensemble comprising both CMIP5 and CMIP6 earth system models. The updated projections show improved physical representations compared to previous projections based on CMIP5 models only. Contrary to the CMIP5 models alone, the new ensemble shows novel and distinct signatures associated with ocean circulation changes in the Bounty Trough that are consistent with recent observations. Previous results are extended to show how the reduced emission scenario SSP126 dampens future trajectories relative to the high emissions scenarios RCP8.5/SSP585 but does not return the end‐of‐century ocean state to that of the “present‐day” period 1976:2005. Furthermore, analysis of archived output from three marine ecosystem models indicates that the south‐west Pacific Ocean total consumer biomass will reduce in the future, with reductions of 25%–51% by end‐of‐century under RCP8.5/SSP585 forcing. Overall, this article provides increased confidence of a substantially modified state of the southwest Pacific Ocean—physical, biogeochemical, and ecological—by end‐of‐century compared to present day.