Authors: Mancini, Giordano; Cazalis, Victor;Lucas, Pablo M.;Santini, Luca;Di Marco, Moreno;

The IUCN Red List is a central tool in biodiversity conservation. To best inform policies, it is crucial that it monitors drivers of extinction consistently, especially those of growing concern, as climate change. However, assessors are currently not able to properly evaluate climate change impact across groups, due to the lack and uncertainty of climate change information and worsened by the discrepancy between “well studied” and “less studied” taxa. For example, 28% of threatened birds are considered threatened by climate change vs 10% of reptiles, despite the latter is a group of ectotherms highly sensitive to temperature. Here, we propose a standardized measure of climate change exposure to improve climate change risk assessment. Using terrestrial mammals as study group, we measure the exposure as the difference between the current and the future species climatic niche, defined using current and future bioclimatic variables. Assuming areas outside the future climatic niche are less likely to be suitable, this measure can directly inform Red List Criterion A on population trends and thus allows to identify species that are likely to be threatened by climate change and should be reassessed. Our measure is potentially applicable to all species within the IUCN with range maps.