Alexander Tomas Sentinella, William B. Sherwin, Catherine A. Offord, Angela T Moles

Understanding how species will respond to climate change is critically important for managing our ecosystems into the future. However, surprisingly little is known about the distribution of risk based on the actual thermal tolerances of species, especially plants. We used germination records from 776 species to provide a global map of plant warming risk – the difference between maximum germination temperature and the predicted 2070 temperature. We then tested a series of hypotheses about factors associated with high risk. Many of our predictions were overturned. For example, although a great deal of attention has been paid to the risks faced by tropical forests, we found that the biomes most at risk were tropical grasslands, savannas and shrublands. Similarly, while we expected Australian species to have a lower warming risk due to its already variable conditions, our data showed that Australia had the highest average warming risk. Conversely, European species faced the lowest risk, with no plants examined in this study predicted to exceed their upper limits by 2070. Plants from regions with higher seasonality and higher canopy cover had lower warming risk, but the absolute range of annual temperature had no effect on risk. Therefore, the underlying factors contributing to warming risk warrant further examination. Overall, our results highlight that the regions most at risk from warming are not necessarily those with the most warming, but regions where species are closest to their upper limits. More attention needs to be given to high risk tropical environments, especially non-forest tropical environments which face the highest risk. In summary, while much of the world’s biota faces substantial threats from climate change, researchers may be surprised about where the effects are most acute.