Reygondeau, G., Cheung, W. W. L., Wabnitz, C. C. C., Lam, V. W. Y., Frölicher, T., & Maury, O. (2020). Climate Change-Induced Emergence of Novel Biogeochemical Provinces. In Frontiers in Marine Science (Vol. 7, p. 657). https://www.frontiersin.org/article/10.3389/fmars.2020.00657
Summary:
The global ocean is commonly partitioned into 4 biomes subdivided into 56 biogeochemical provinces (BGCPs). Each province corresponds to a unique regional environment that shapes biodiversity and constrains ecosystem structure and functions. Biogeochemical provinces are dynamic entities that change their spatial extent and position with climate and are expected to be perturbated in the near future by global climate change. In this study, the changes in spatial distribution of BGCPs from 1950 to 2100 using three earth system models under two representative concentration pathways (RCP 2.6: zero CO2 emissions by 2100 and RCP 8.5: “no mitigation”) were characterised. Projection of the future distribution of BGCPs also revealed the emergence of new climate that has no analog with past and current environmental conditions. These novel environmental conditions, are named No-Analog BGCPs State (NABS), will cover areas where a substantial proportion of global marine biodiversity presently occurs and with a crucial dependence on seafood production and will expand from 2040 to 2100 at a rate of 4.3 Mkm2 per decade (1.2% of the global ocean). The NABS were characterized by very warm mean annual temperatures, high salinity, low oxygen concentration and low net primary production. Most marine species will be physiologically stressed under such conditions, which could impact their survival rate. This study subsequently quantified the potential number of marine species and annual volume of fisheries catches that would experience such novel environmental conditions to roughly evaluate the impact of NABS on ecosystem services. If the global climate is not kept below 2°C warming, NABS areas can be expected to emerge, as early as 20 years from the 2010s. It would affect 19% of the total number of exploited species in 2050 and 59% in 2100 and would cover regions that are currently responsible for 8% of global marine fisheries catch in 2050 and 30% in 2100, under RCP 8.5. These numbers would change to only 15% of exploited species and 5% of total fisheries catches in NABS areas by the end of the 21st century under the RCP 2.6 scenario. Mitigating anthropogenic pressures at a level sufficient to reach the Paris agreement targets would therefore substantially reduce the risk of emergence of large NABS regions in the global ocean, and the dramatic consequences that such large-scale ecological changes would entail for tropical marine biodiversity, associated fisheries and the human communities that they support.
Policy relevant message:
The environmental changes that would occur in the global ocean along a “no mitigation” RCP 8.5 scenario would lead to a drastic reorganization of global marine biogeography, associated biodiversity and trophic networks. If the global climate is not kept below 2°C warming, these novel areas can be expected to emerge, as early as 20 years from the 2010s. It would affect 19% of the total number of exploited species in 2050 and 59% in 2100 and would cover regions that are currently responsible for 8% of global marine fisheries catch in 2050 and 30% in 2100, under RCP 8.5. These numbers would change to only 15% of exploited species and 5% of total fisheries catches in these novel areas by the end of the 21st century under the RCP 2.6 scenario (zero CO2 emissions by 2100). Mitigating anthropogenic pressures at a level sufficient to reach the Paris agreement targets would therefore substantially reduce the risk of emergence of large NABS regions in the global ocean, and the dramatic consequences that such large-scale ecological changes would entail for tropical marine biodiversity, associated fisheries and the human communities that they support.