[A-CG34] 地球規模環境変化の予測と検出

[ACG34-09] How do afforestation and BECCS differ in their impacts on the land carbon cycle and surface climate?

*Irina Melnikova^1,2、Philippe Ciais²、Katsumasa Tanaka^1,2、Nicolas Vuichard²、Olivier Boucher³ (1.National Institute for Environmental Studies (NIES), Japan、2.Laboratoire des Sciences du Climat et de l’Environnement (LSCE), France、3.Institut Pierre-Simon Laplace (IPSL), France)

キーワード：afforestation, BECCS, carbon cycle, CDR, land-based solutions, temperature overshoot

Carbon dioxide removal (CDR) plays an essential role in achieving the Paris Agreement targets. Bioenergy with carbon capture and storage (BECCS) and Afforestation and reforestation (AR) are two widely assumed CDR methods in future mitigation pathways. We compare their CDR potentials and impacts on the land carbon cycle and surface climate by using Earth System Model simulations under the SSP5-3.4-OS temperature overshoot pathway, which favors BECCS over AR, combined with additional simulations assuming AR instead of BECCS based on the land-use maps of SSP5-3.4-OS. BECCS removes more carbon from the atmosphere than AR does in allocated areas. However, land-use change-induced CO₂ release regionally offsets the CDR benefits of BECCS over AR, depending on the carbon capture and storage efficiency of bioenergy crops and the timescales required to achieve the mitigation targets. Under the overshoot scenario considered, BECCS can remove more carbon from the atmosphere in the long term, but AR is more beneficial than BECCS in the short term (20–30 years) globally, except for some parts of the Middle East and Africa. Besides, the potential CDR benefits are compromised by regionally contrasting climate impacts from different surface properties of bioenergy crops and forests (albedo, roughness, surface humidity, extreme heats). From the biogeophysical perspective, BECCS may be more beneficial in the target areas of the high- and mid-latitudes of the Northern Hemisphere, where it causes local cooling through radiative mechanisms. AR is more beneficial in most parts of subtropical and tropical subregions of the Southern Hemisphere, where it causes local cooling through non-radiative mechanisms. The decision to allocate land for bioenergy crops or forests should take into account their respective CDR potentials, as well as their associated biogeochemical and biogeophysical feedbacks. This study may have important implications for regional and local mitigation strategies.