Department of Environmental Systems Science, Institute for Environmental Decisions, ETH Zurich (Swiss Federal Institute of Technology), Zurich, Switzerland.
PLoS One. 2021 Mar 17;16(3):e0247887. doi: 10.1371/journal.pone.0247887. eCollection 2021.
The Representative Concentration Pathway 2.6 (RCP2.6), which is broadly compatible with the Paris Agreement's temperature goal by 1.5-2°C, contains substantial reductions in agricultural non-CO2 emissions besides the deployment of Carbon Dioxide Removal (CDR). Failing to mitigate agricultural methane and nitrous oxide emissions could contribute to an overshoot of the RCP2.6 warming by about 0.4°C. We explore using additional CDR to offset alternative agricultural non-CO2 emission pathways in which emissions either remain constant or rise. We assess the effects on the climate of calculating CDR rates to offset agricultural emission under two different approaches: relying on the 100-year global warming potential conversion metric (GWP100) and maintaining effective radiative forcing levels at exactly those of RCP2.6. Using a reduced-complexity climate model, we find that the conversion metric leads to a systematic underestimation of needed CDR, reaching only around 50% of the temperature mitigation needed to remain on the RCP2.6 track. This is mostly because the metric underestimates, in the near term, forcing from short-lived climate pollutants such as methane. We test whether alternative conversion metrics, the GWP20 and GWP*, are more suitable for offsetting purposes, and found that they both lead to an overestimation of the CDR requirements. Under alternative agricultural emissions pathways, holding to RCP2.6 total radiative forcing requires up to twice the amount of CDR that is already included in the RCP2.6. We examine the costs of this additional CDR, and the effects of internalizing these in several agricultural commodities. Assuming an average CDR cost by $150/tCO2, we find increases in prices of up to 41% for beef, 14% for rice, and 40% for milk in the United States relative to current retail prices. These figures are significantly higher (for beef and rice) under a global scenario, potentially threatening food security and welfare. Although the policy delivers a mechanism to finance the early deployment of CDR, using CDR to offset remaining high emissions may well hit other non-financial constraints and can thus only support, and not substitute, emission reductions.
路径 2.6（RCP2.6）与《巴黎协定》1.5-2°C 的温度目标大致相符，除了部署二氧化碳去除（CDR）之外，还大幅减少了农业非二氧化碳排放。未能减轻农业甲烷和氧化亚氮排放可能导致 RCP2.6 升温超过约 0.4°C。我们探讨了使用额外的 CDR 来抵消替代农业非二氧化碳排放途径的方法，这些途径要么保持不变，要么上升。我们评估了根据两种不同方法计算 CDR 率以抵消农业排放对气候的影响：依赖于 100 年全球变暖潜能值（GWP100）转换指标和将有效辐射强迫水平保持在 RCP2.6 的水平。使用简化复杂性气候模型，我们发现转换指标会导致对所需 CDR 的系统低估，仅达到保持在 RCP2.6 轨道上所需的温度缓解的 50%左右。这主要是因为该指标在短期内低估了甲烷等短寿命气候污染物的强迫。我们测试了替代转换指标，GWP20 和 GWP*，是否更适合抵消目的，发现它们都导致对 CDR 要求的高估。在替代农业排放途径下，保持 RCP2.6 总辐射强迫需要的 CDR 量最多是已经包含在 RCP2.6 中的两倍。我们研究了这种额外 CDR 的成本，以及将其纳入几种农业商品中的影响。假设 CDR 的平均成本为 150 美元/吨二氧化碳，我们发现与当前零售价格相比，美国的牛肉价格上涨了 41%，大米价格上涨了 14%，牛奶价格上涨了 40%。在全球情景下，这些数字（对牛肉和大米而言）要高得多，可能会威胁到粮食安全和福利。尽管该政策提供了一种为早期部署 CDR 提供资金的机制，但使用 CDR 来抵消剩余的高排放可能会遇到其他非金融约束，因此只能支持，而不能替代减排。
