How Low Can We Go? The Implications of Delayed Ratcheting and Negative Emissions Technologies on Achieving Well Below 2 °C
How Low Can We Go? The Implications of Delayed Ratcheting and Negative Emissions Technologies on Achieving Well Below 2 °C
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我们能降到多低？延迟棘轮和负排放技术对实现远低于 2 °C 的影响
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发表时间：
2018
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影响因子：
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通讯作者：
Daniel Welsby
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作者：
M. Winning;S. Pye;J. Glynn;D. Scamman;Daniel Welsby
国家自主贡献（NDC）中包含的承诺代表着从全球“无政策”路径走向最佳长期全球缓解路径的过渡步骤。然而，《巴黎协定》的目标凸显出目前的承诺还不够。因此，有必要在短期内加大各方未来的减排承诺。保持远低于 2°C 并力争将气温降低到 1.5°C 的雄心勃勃的目标意味着，任何延迟提高承诺的代价都可能极其高昂，甚至可能使目标无法实现。在本章中，我们考虑推迟到 2030 年对全球排放轨迹向 2°C 和 1.5°C 的影响，以及通过负排放技术 (NET) 进行抵消的作用。分析表明，如果没有极高水平的负排放技术（NET），例如碳捕获和存储与生物能源（BECCS）相结合，那么延迟行动会使实现 1.5°C 目标变得尤其困难。根据生物质的可用性，将需要 BECCS 之外的其他 NET。政策制定者还必须认识到，化石燃料的前景与净能源的前景密切相关。如果 NET 无法扩展，则本分析中建议的化石燃料水平与《巴黎协定》目标不相容，即存在锁定高化石燃料未来的风险。因此，决策者必须充分理解不同策略的风险。
Pledges embodied in the nationally determined contributions (NDCs) represent an interim step from a global “no policy” path towards an optimal long-term global mitigation path. However, the goals of the Paris Agreement highlight that current pledges are insufficient. It is, therefore, necessary to ratchet-up parties’ future mitigation pledges in the near-term. The ambitious goals of remaining well below 2 °C and pursuing reductions towards 1.5 °C mean that any delay in ratcheting-up commitments could be extremely costly or may even make the targets unachievable. In this chapter, we consider the impacts of delaying ratcheting until 2030 on global emissions trajectories towards 2 °C and 1.5 °C, and the role of offsets via negative emissions technologies (NETs). The analysis suggests that delaying action makes pursuing the 1.5 °C goal especially difficult without extremely high levels of negative emissions technologies (NETs), such as carbon capture and storage combined with bioenergy (BECCS). Depending on the availability of biomass, other NETs beyond BECCS will be required. Policymakers must also realise that the outlook for fossil fuels are closely linked to the prospects for NETs. If NETs cannot be scaled, the levels of fossil fuels suggested in this analysis are not compatible with the Paris Agreement goals i.e. there are risks of lock-in to a high fossil future. Decision makers must, therefore, comprehend fully the risks of different strategies.