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.

中文翻译：

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关于实现长期温度目标所需的农田和林区扩展的可行性

基于生物质的负排放技术（NETs），例如具有碳捕获和封存的生物能源（BECCS）和造林/再造林（AR），被视为实现《巴黎协定》规定的2°C和1.5°C目标的重要选择，但是他们大规模部署的可行性仍然非常不确定。这项研究的重点是与基于生物质的NET相关的土地利用区域的扩张速度，并评估了缓解气候变化方案实现温度目标的可行性。我们的模型分析表明，在全球最低成本措施的假设下，撒哈拉以南非洲的农田总面积（包括能源农田）和未来几十年许多地区的碳汇人工林面积都需要以前所未有的速度扩张用于CO ₂减排。另一方面，如在现实世界中所观察到的那样，当土地利用扩张的速度受到限制时，在本世纪中叶左右，CO ₂减排成本将变得不切实际地高，尤其是在目标温度为1.5°C的情况下；由于土地利用扩张的速度有限，相对低成本的措施（如撒哈拉以南非洲的BECCS和许多地区的AR）的部署受到限制，而能源系统必须转换为几乎为零净/负的CO ₂为2°C / 1.5°C的目标排放，必须使用成本更高的其他缓解技术。这些结果可能引起人们对实现温度目标（尤其是针对1.5°C目标温度）的可行性的关注，并指出技术和方案设计方面需要对基于生物质的NET及其允许的扩展速度进行进一步研究。