Characterization factor estimation based on a species-specific extinction risk approach for determining CO2 emission impact on terrestrial biodiversity

Species extinction risk is a crucial indicator of the global impact of climate change on biodiversity. In life cycle impact assessment (LCIA), the relationship between the potentially extinct ratio and temperature is used to calculate characterization factors (CFs) that indicate additional biodiversity impact per unit greenhouse gas emissions, using the biodiversity loss indicator termed potentially disappeared fraction (PDF). However, current methods for calculating CFs that focus on terrestrial biodiversity do not show differences among taxa and regions. Here, we estimated taxon-level CFs based on a species-specific extinction risk approach for determining impact of CO2 emission on terrestrial biodiversity. The extinction risk of a species is defined as the reciprocal of the estimated waiting times for extinction caused by climate-derived habitat loss of the species. Based on the approach, CFs for five taxa—birds, reptiles, mammals, amphibians, vascular plants—were estimated as 0.017, 0.017, 0.025, 0.027, and 0.040 (PDF·km2·year·kton−1), respectively. In addition, CFs that use the number of potentially extinct species (species·kton−1) as indicators were also calculated based on the same species-specific extinction risk approach. The proposed method successfully calculates taxon-level CFs and has the potential to show their regional variations, which contributes to the precise impact assessment on climate-derived biodiversity in LCIA.