A bioenergy-focused versus a reforestation-focused mitigation pathway yields disparate carbon storage and climate responses

Limiting global warming to 2 degrees C requires urgent action on land - based mitigation. This study evaluates the biogeochemical and biogeophysical implications of two alternative land - based mitigation scenarios that aim to achieve the same radiative forcing. One scenario is primarily driven by bioenergy expansion (SSP226Lu- BIOCROP), while the other involves re/afforestation (SSP126Lu- REFOREST). We find that overall, SSP126Lu- REFOREST is a more efficient strategy for removing CO2 from the atmosphere by 2100, resulting in a net carbon sink of 242 - 483 PgC with smaller uncertainties compared to SSP226Lu- BIOCROP, which exhibits a wider range of -78 - 621 PgC. However, SSP126Lu- REFOREST leads to a relatively warmer planetary climate than SSP226Lu- BIOCROP, and this relative warming can be intensified in certain re/afforested regions where local climates are not favorable for tree growth. Despite the cooling effect on a global scale, SSP226Lu- BIOCROP reshuffles regional warming hotspots, amplifying summer temperatures in vulnerable tropical regions such as Central Africa and Southeast Asia. Our findings highlight the need for strategic land use planning to identify suitable regions for re/afforestation and bioenergy expansion, thereby improving the likelihood of achieving the intended climate mitigation outcomes. Significance Our study compares two land - based mitigation scenarios that limit global warming to 2 degrees C, primarily driven by bioenergy expansion and re/afforestation. While the re/afforestation- focused scenario excels in CO2 removal with lower uncertainties, it could lead to a relatively warmer regional climate than the bioenergy expansion-focused scenario, especially in regions unfavorable for tree growth. Despite the global cooling effect, the bioenergy expansion- focused approach, however, reshuffles regional warming hotspots, potentially amplifying summer temperatures in vulnerable regions such as Central Africa and Southeast Asia. Our study highlights the importance of carefully locating suitable re/afforestation and bioenergy expansion regions for achieving intended climate mitigation outcomes. Our research provides valuable insights for future land use planning and policy decisions to mitigate climate change.