On the feasibility of cropland and forest area expansions required to achieve long-term temperature targets

Abstract

Biomass-based negative emission technologies (NETs) such as bioenergy with carbon capture and storage (BECCS) and afforestation/reforestation (AR) are regarded as important options to achieve the 2 °C and 1.5 °C targets stipulated in the Paris agreement, but the feasibility of their large-scale deployments remains very uncertain. This study focused on the speed of expansions of land-use area related to the biomass-based NETs and assessed the feasibility of climate change mitigation scenarios to achieve the temperature targets. Our model analysis shows that expansions at unprecedented speeds are required for total cropland area (including energy cropland) in Sub-Saharan Africa and for planted forest area for carbon sink in many regions in the next decades, under the assumption of global least-cost measures for CO2 emission reduction. On the other hand, when the speed of the land-use expansions is limited as observed in the real world, the CO2 emission reduction costs become unrealistically high around the middle of this century, particularly in scenarios for the 1.5 °C target; relatively low-cost measures such as BECCS in Sub-Saharan Africa and AR in many regions are limited in deployment due to the limited speed of the land-use expansion, and yet energy systems must be transformed to nearly net-zero/negative CO2 emissions for the 2 °C/1.5 °C target, which necessitates using other mitigation technologies of much higher costs. These results may cause concern over the feasibility of achieving the temperature targets, especially for the 1.5 °C target, and point to technical and scenario design aspects that will need further research for biomass-based NETs and their allowable expansion speed.