Climate change and biodiversity loss pose significant threats to human well-being and sustainability. The Paris Agreement aims to limit global warming, necessitating substantial carbon dioxide removal (CDR). Integrated Assessment Models (IAMs) often rely heavily on land-based CDR, such as BECCS and afforestation, to achieve climate stabilization targets. However, large-scale implementation of these measures raises concerns about potential negative impacts on regional biodiversity. This study addresses this concern by quantitatively assessing the impacts of large-scale BECCS and afforestation on both global and regional biodiversity, considering the equity and sustainability implications.

Existing research highlights the potential co-benefits of climate mitigation and biodiversity conservation, but there's limited understanding of the regional impacts of large-scale land-based CDR. Previous studies have acknowledged the potential negative impacts of BECCS and afforestation on biodiversity, particularly habitat loss and alteration of species composition. The need for a comprehensive evaluation of the trade-offs between climate mitigation goals and regional biodiversity conservation is widely recognized. This study builds on this literature by using a sophisticated integrated modeling framework to provide quantitative assessments of these trade-offs.

The study used the Asia-Pacific Integrated Model (AIM) framework, incorporating energy-economic systems, spatially explicit land use, and biodiversity. Four scenarios were considered: a baseline (no mitigation), 2C-BECCS (CDR primarily through BECCS), 2C-Aff (CDR primarily through afforestation), and 2C-Opt (optimal combination of BECCS and afforestation). All mitigation scenarios aimed for approximately 1000 GtCO2 cumulative emissions by 2100. The model projected land-use change, carbon sequestration, and biodiversity changes (species richness and composition) from 2030 to 2090 for 8428 species across five taxonomic groups. Climate change impacts were also considered using climate scenario data. The study further analyzed regional variations in biodiversity impacts, linking them to land-use change, carbon sequestration, and GDP per capita. To isolate the effects of climate change and land-use change, the authors conducted separate analyses using climate-only and land-use-only models.

Globally, climate mitigation efforts reduced biodiversity loss compared to the baseline scenario, regardless of the specific land-based CDR measures employed. However, regional impacts varied considerably. Regions with higher contributions to land-use change and carbon sequestration experienced greater biodiversity loss. BECCS generally resulted in less biodiversity loss than afforestation due to a smaller land-use change footprint. Specific negative impacts were observed in grassland ecosystems in various regions (South America, Sub-Saharan Africa, East Asia, and Oceania). The conversion of pasture to cropland for BECCS and of natural land to forest for afforestation negatively impacted biodiversity in several areas. In contrast, some limited positive impacts were observed in regions where pasture was converted to forest. Economic regions contributing more to carbon sequestration tended to suffer greater biodiversity loss. However, mitigation measures showed a tendency to lessen biodiversity loss in regions with lower GDP per capita, though the effect was not uniformly strong. Analyses using climate-only and land-use-only models helped to disentangle the specific impacts of each factor.

The findings highlight the complex interplay between climate mitigation and biodiversity conservation. While climate mitigation is crucial, the choice of land-based CDR measures significantly influences regional biodiversity impacts. The regional disparities in biodiversity impacts underscore the need for equitable mitigation strategies. The greater biodiversity loss associated with afforestation compared to BECCS, despite similar carbon sequestration, emphasizes the importance of considering land-use change as a key factor in mitigation planning. The observed impact on high-latitude and high-altitude regions suggests potential trade-offs between mitigating the negative impacts of climate change in these regions (range shifts of species) and maintaining endemic species composition. Nature-based solutions (NbS) could potentially offer a more sustainable and equitable approach to CDR, minimizing land-use changes and promoting biodiversity.

Climate change mitigation is crucial for biodiversity conservation. However, land-based CDR measures, such as BECCS and afforestation, while contributing to climate stabilization, can cause regional biodiversity loss, particularly in grassland ecosystems. The choice of mitigation measures should carefully consider both global and regional biodiversity impacts. Further research should investigate the potential of NbS and other alternative CDR options, considering both carbon sequestration and biodiversity conservation. Reducing anthropogenic GHG emissions remains crucial to minimize the reliance on land-based CDR and its associated impacts.

The study treats bioenergy cropland as equivalent to normal cropland, lacking detailed information on the biodiversity impacts of specific bioenergy crops and management practices. Similarly, the lack of precise information on the type and structure of planted forests limited the analysis of afforestation's biodiversity impacts. The model's reliance on species distribution models and certain assumptions about dispersal abilities may also introduce uncertainty into the projections. Finally, the study focuses on a specific set of mitigation scenarios and may not fully capture the range of potential future pathways.