Assessment of global warming impact on biodiversity using the extinction risk index in LCIA: a case study of Japanese plant species

There has been an increasing number of studies on species extinction because of global warming based on estimations of changes in species distributions. Life cycle impact assessment methods do not have a biodiversity damage factor for global warming that uses the extinction risk index. In this study, a method for determining the extinction risks of individual species per unit CO₂ emission was proposed and test calculations of the extinction risks of 216 species of Japanese vascular plants were performed. We also examined the possibility of determining local and global extinction risk factors using this method.

This method uses the Expected Increase in the Number of Extinction Species (EINES), which is defined as the inverse of the time to extinction, as the extinction risk index. Procedures for determining the extinction risks of individual species per unit CO₂ emission (EINES/species/kg) are as follows. First, based on the base scenario of CO₂ emission, a niche-based species distribution model is used to estimate species distribution areas in 2000 and 2100 and calculate the distribution area decrease over 100 years. The number of years before the zero distribution area is then determined by assuming that the decrease is constant. Extinction risk is defined as the inverse of this time. The final step is to determine the extinction risk at specific CO₂ emissions in addition to the base emission scenario and divide the difference in the extinction risk by the additional amount of CO₂ emissions.

The distribution areas of 216 species of Japanese vascular plants having southern distribution limits were estimated to decrease by 40–85% in 100 years. The accuracy of the estimation was sufficient according to the value of area under the curve (AUC). Considering climate models and migration conditions, the extinction risk per unit CO₂ emission was estimated between −0.6 × 10⁻¹⁸ and 4.7 × 10⁻¹⁸ (EINES/species/kg). We converted the normalization values of the extinction risk of Japan for the 216 species to compare impact of land use changes and waste processing with that of global warming on the species. We found that global warming has smaller impact compared with land use changes and larger impact compared with waste processing.

A method for estimating the extinction risks of species per unit CO₂ emission was proposed, and it can be used to determine the local and global extinction risk factors of CO₂.