Beyond the single-basket mindset: A multi-gas approach to better constrain overshoot in near term warming

Julie S Miller, Gabrielle Dreyfus, John S Daniel, Stephen Willis, Yangyang Xu
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Abstract

The remaining carbon budget framework tracks progress towards the Paris Agreement’s goal to limit longer-term warming to well below 2 ºC, but no analogous framework exists for constraining mid-century warming. Established single-basket methods of combining gases into CO2-equivalents using Global Warming Potentials (GWPs) lead to ambiguity over what combination of short- and long-lived emissions reductions are needed because they obscure the distinct warming impacts of each. We investigate to what extent a multi-basket approach that separates short-lived and long-lived pollutants can better estimate the likelihood for emission pathways to meet a near-term warming goal. We develop logistic regression models to categorize IPCC emission pathways (AR6) based on whether they exceed a mid-century temperature threshold. We focus on two baskets, using CO2 for long-lived and methane (CH4) for short-lived gases. For comparison, we consider several single-basket approaches (e.g., GWP100, GWP20, GWP*). We further apply our framework to a synthetic dataset covering a broader emissions space. Across both datasets, the two-basket outperforms all single-baskets. Using an illustrative near-term goal (1.7ºC), the two-basket approach reduces the magnitude of overshoot by a factor of 7 compared with the traditional single-basket. The two-basket’s advantage is smaller with the AR6 pathways, which we attribute to the high correlation between CO2 and CH4 emissions and confounding effects from other pollutants. Our results indicate that the two-basket approach better constrains overshoot magnitude, particularly if future emissions deviate from the AR6 assumption of correlated CO2 and CH4 reductions. Our approach allows the determination of a metric value and reduction target in the context of a chosen set of scenarios and temperature threshold; the outcome is a near-term methane-specific emissions budget that can be adopted by decisionmakers in a way that is analogous and complementary to the carbon budget. Future work could consider a third basket for very short-lived pollutants.
超越单篮子思维:采用多种气体方法更好地限制近期变暖超调
剩余的碳预算框架可跟踪《巴黎协定》将长期升温限制在远低于 2 ºC 的目标的进展情况,但在限制本世纪中期升温方面却没有类似的框架。使用全球升温潜能值(GWPs)将各种气体合并成二氧化碳当量的单篮子既定方法会导致短期和长期减排量的组合模糊不清,因为它们掩盖了每种减排量对升温的不同影响。我们研究了将短寿命和长寿命污染物分开的多篮子方法能在多大程度上更好地估计排放路径实现近期变暖目标的可能性。我们建立了逻辑回归模型,根据 IPCC 排放路径(AR6)是否超过本世纪中期温度阈值对其进行分类。我们将重点放在两个篮子上,长寿命气体使用二氧化碳,短寿命气体使用甲烷 (CH4)。为了进行比较,我们考虑了几种单篮子方法(如 GWP100、GWP20、GWP*)。我们还将我们的框架应用于一个涵盖更广泛排放空间的合成数据集。在这两个数据集上,双篮子都优于所有单篮子。以一个说明性的近期目标(1.7ºC)为例,与传统的单篮子方法相比,双篮子方法将超调幅度降低了 7 倍。在 AR6 途径中,双篮子方法的优势较小,我们将其归因于二氧化碳和甲烷排放之间的高度相关性以及其他污染物的混杂效应。我们的结果表明,双篮子方法能更好地限制超调幅度,尤其是在未来排放量偏离 AR6 假设的二氧化碳和甲烷相关减排量的情况下。我们的方法允许在一组选定的情景和温度阈值的背景下确定一个度量值和减排目标;其结果是决策者可以采用与碳预算类似和互补的方式,制定针对甲烷的近期排放预算。未来的工作可以考虑为寿命极短的污染物设计第三个篮子。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
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