Disentangling diverse responses to climate change among global marine ecosystem models

Next-generation ensemble projections reveal higher climate risks for marine ecosystems

“…Warming can affect metabolic costs, rates of biomass production, mortality and species distributions and interactions in individual MEMs; a detailed study of the response of individual MEMs to warming in isolation 21 revealed a substantial variability in mechanisms and responses, although a broadly consistent negative impact on biomass. Warming is also accompanied by increased ocean stratification and a marked biomass decrease of non-nitrate-fixing phytoplankton 23 .…”

“…These differences within Fish-MIP represent structural variability in the MEMs, and the sensitivity of the results, as well as the general agreement, should be seen as a test of how robust the result of declining MEM biomass under climate change is to the ecological and other assumptions of the MEMs. Variability in how lower trophic levels are included in MEMs can result in a range of directional changes even under the same climate simulation experiment, highlighting the need for improvement in the coupling of MEMs with biogeochemical variable outputs 21 . However, the fact that all MEMs projected declining biomass under high emissions despite these differences around lower-trophic-level forcing suggests a robustness to the results and perhaps the particular importance of temperature effects 21 .…”

“…Variability in how lower trophic levels are included in MEMs can result in a range of directional changes even under the same climate simulation experiment, highlighting the need for improvement in the coupling of MEMs with biogeochemical variable outputs 21 . However, the fact that all MEMs projected declining biomass under high emissions despite these differences around lower-trophic-level forcing suggests a robustness to the results and perhaps the particular importance of temperature effects 21 .…”

“…We also caution that none of the MEMs (or ESMs for plankton) yet includes the potential for adaptation or evolution of individual taxa and that there remains the lack of a full bi-directional coupling between higher- and lower-trophic-level (biogeochemical) processes in the MEMs. Furthermore, many species interactions are not well captured by global-scale MEMs, and the potential for nonlinear tipping points that cause rapid ecological deterioration remains unclear 21 .…”

“…Notably, the MEM model agreement (Extended Data Fig. 7e,f ) is fairly high (>80%) in most oceanic regions under CMIP6, except for the subtropical gyres where the agreement drops to 50% (maximum disagreement among models), probably due to the marked differences in CMIP6 NPP and the various ways MEMs incorporate lower-trophic-level forcing 21 . Regardless of whether the full or comparable MEM models are considered (Extended Data Figs.…”