Biodiversity Loss Projections Under SSP Scenarios

Abstract

The Shared Socioeconomic Pathways (SSPs) provide a structured scenario framework for projecting biodiversity loss under alternative combinations of climate change and land-use trajectories, enabling policy-relevant quantification of the consequences of different societal development choices for global vertebrate and plant diversity. This study conducted the most comprehensive SSP-based biodiversity projection analysis yet attempted, modelling projected species richness change and extinction risk for 38,247 vertebrate and plant species across five SSP scenarios (SSP1-1.9, SSP1-2.6, SSP2-4.5, SSP3-7.0, SSP5-8.5) by 2050 and 2100. Species distribution models (MaxEnt; 10-fold cross-validation AUC >= 0.84 for all species) were coupled with shared land-use change scenarios from the ISIMIP3b protocol and CMIP6 climate projections from six global circulation models. Under SSP5-8.5 by 2100, 21.4% +- 4.2% of modelled species lose >= 50% of their current suitable habitat -- more than double the 8.7% +- 2.1% projected under SSP1-1.9. Tropical amphibians and endemic island species face the highest absolute risks: 47.8% +- 8.4% of tropical amphibian species lose >= 30% of habitat under SSP3-7.0, rising to 68.4% under SSP5-8.5. Combined climate-and-land-use projections consistently produce greater biodiversity loss than either driver alone (synergistic interaction in 74.8% of species), confirming that biodiversity policy frameworks must address both drivers simultaneously. The Kunming-Montreal GBF 30x30 protected area target, when applied to areas of highest projected species loss, reduces SSP3-7.0 extinctions by 34.7% -- the largest conservation intervention benefit identified by the scenario analysis.