Fig. 4. Impacts of projected climate change on global marine biomass and heterotrophic respiration in epipelagic (<200 m) waters.

Relative (%) change in global a biomass, and c respiration; and global b biomass lost (Pg wet biomass); and d additional respiration (Pg C yr⁻¹) from prokaryotes, zooplankton (covering micro-, meso- and macro-zooplankton) and fish in the top 200 m, under Shared Socioeconomic Pathway 3-7.0, compared to 1980–2000 levels. Contemporary (1980–2000) global biomass of prokaryotes (1.7 Pg) was calculated using statistical models derived here (assuming a carbon-to-biomass ratio of 0.1; see the “Methods” section). Global contemporary biomass of phytoplankton (5.4 Pg), zooplankton (7.9 Pg), and fish (5.5 Pg) were obtained from Hatton et al. (2021)³, while respiration of zooplankton (12.4 Pg C yr⁻¹) and fish (1.0 Pg C yr⁻¹) were taken from Nowicki et al.⁵ and Bianchi et al.⁴⁵, respectively. Contemporary global prokaryotic respiration (22.6 Pg C yr⁻¹) was calculated using statistical models derived here (see the “Methods” section). In a and c, solid lines represent the ensemble mean change, and shaded areas are the standard deviation from four separate simulations, each forced by one of four earth-system models (see the “Methods” section). Source data are provided as a Source Data file.