The high value of climate mitigation for global fish biomass to 2300

As climate change progresses, increasing attention is being devoted to potential impacts on ecosystems and resources under sustained warming. For models that resolve climate impacts on global marine animal biomass, however, most work to date including model intercomparisons have largely focused on the period up to 2100. Here we consider projections to 2300 using a collection of five Marine Ecosystem Models (BOATS, FEISTY, DBPM, MArcroecological, and ZooMSS) driven by output from a collection of CMIP6 Earth system models (including CESM2-WACCM and IPSL-CM6A, as well as UKESM1, MIROC-ES2L, and ACCESS-ESM1.5). Initial results from ESMs with online coupled biogeochemical models suggest that although they exhibit a degree of diversity in their ocean warming response, their disagreements about projected primary production are even more pronounced, with the disagreements being not only in amplitude but also in sign.

We explore the long-term impacts of climate mitigation on marine animal biomass, by comparing Marine Ecosystem Model results under high emissions with low mitigation (SSP5-8.5) and low emissions with high mitigation (SSP1-2.6) forcing. If thermal forcing were to dominate the fish biomass through its effect on mortality with a linear response, one might expect an approximately factor of five difference between SSP1-2.6 and SSP5-8.5 projections of marine animal biomass change to 2300. Both regional and global aspects will be considered, with a focus on identifying potential tipping points under SSP5-8.5 forcing that may be avoided through mitigation.