SPECIES DISTRIBUTION PROJECTIONS UNDER INTERNAL CLIMATE VARIABILITY REVEAL MULTIPLE PLAUSIBLE FUTURES REQUIRING FLEXIBLE CLIMATE-READY DECISIONS

ABSTRACT Traditional biodiversity projections using species distribution models (SDMs) assume that a given emissions pathway implies a largely predictable ecological response, yet how internal climate variability (ICV) translates into SDM outcomes remains largely uncharacterized. By projecting distributions for 34 marine and terrestrial species across 100 initial-condition members from CESM2-LENS2, we show that ICV alone produces qualitatively different outcomes, including reversals in projected range shifts. We classify these outcomes into four decision-relevant cases of increasing ICV susceptibility and find a pronounced marine-terrestrial divide that persists across time horizons. Responsiveness to ICV is not consistently explained by traits or local climate variability amplitude, implying it is atleast partly ecological in nature. Robust biodiversity planning therefore requires decisions stress-tested across distributions of plausible climate realizations rather than single best-estimate maps.