Integrating climate storylines and time of emergence on vulnerability assessments: the case of crested penguins

Anthropogenic climate forcing is altering ocean circulation and water mass distribution across the Southern Ocean, reshaping the habitat of circumpolar marine predators such as threatened crested (Eudyptes) penguins. Understanding species vulnerability remains challenging due to substantial uncertainties in climate projections. Here, we integrate two state-of-the-art climate assessment tools—storylines and time of emergence—to evaluate the vulnerability of crested penguins to ocean warming while explicitly addressing projection uncertainties. Using this framework, we select a discrete set of projections from the Coupled Model Intercomparison Project Phase 6 (CMIP6) that capture qualitatively different global circulation responses and climate sensitivity. Uncertainty in global atmospheric circulation responses, particularly the degree of intensification of the Westerlies, strongly influences both the magnitude and spatial pattern of projected sea surface temperature (SST) warming within penguin foraging habitats. Storylines and climate sensitivity explain a greater proportion of overall projection uncertainty compared to conventional CMIP6 scenario ensembles. We identify two groups of SST sensitivity among crested penguins: (1) highly sensitive species, including Northern Rockhoppers (E. moseleyi) and Aotearoa/New Zealand endemic species, and (2) species with broader distributions, such as Southern and Eastern Rockhoppers (E. chrysocome) and Macaroni/Royal penguins (E. chrysolophus/E. schlegeli), which exhibit spatially heterogeneous exposure and sensitivity. Spatial variability in exposure among widely distributed species highlights opportunities for targeted monitoring to detect early climate change impacts. However, limited data on population dynamics, gene flow, and foraging ecology constrain vulnerability assessments, emphasizing the need for expanded ecological and tracking studies coupled with environmental monitoring. We advocate for interdisciplinary, uncertainty-aware approaches and transparent workflows, including open data and code sharing, to strengthen future climate vulnerability assessments for threatened species.