Two approaches are predominant in climate models: cost–benefit and cost-effectiveness analysis. Cost–benefit analysis maximizes welfare, finding a trade-off between climate damages and emission abatement costs. By contrast, cost-effectiveness analysis minimizes abatement costs, omits damages but adds a climate constraint, such as a radiative forcing constraint, a temperature constraint or a cumulative emissions constraint. We analyse the impacts of these different constraints on optimal carbon prices, emissions and welfare. To do so, we fit a model with abatement costs, capital repurposing costs (stranded assets) and technological change on IPCC and NGFS scenarios. For scenarios reaching 1.5 °C in 2100, a constraint on cumulative emissions has the best welfare properties, followed by a temperature constraint with overshoot. A forcing constraint with overshoot has insufficient early abatement and large net negative emissions later on, leading to a substantial welfare loss of $23 Trillion. As to the paths reaching 2 °C, all cost-effectiveness analysis abate too late, but the welfare impact of this dynamic inefficiency is milder. Again, a forcing constraint with overshoot scores worst. We show that large negative emissions at the end of the century are never optimal and an artefact of constraints with overshoot.

中文翻译：

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气候目标的福利特性


气候模型中有两种主要方法：成本效益和成本效益分析。成本效益分析使福利最大化，在气候损害和减排成本之间找到权衡。相比之下，成本效益分析可以最大限度地降低减排成本，忽略损害，但会增加气候约束，例如辐射强迫约束、温度约束或累积排放约束。我们分析了这些不同约束条件对最佳碳价格、排放和福利的影响。为此，我们在 IPCC 和 NGFS 情景中拟合了一个包含减排成本、资本再利用成本（搁浅资产）和技术变革的模型。对于 2100 年达到 1.5 °C 的情景，对累积排放的约束具有最好的福利特性，其次是具有过冲的温度约束。超调的强制约束在早期减排方面作用不足，后期净负排放量很大，导致 23 万亿美元的重大福利损失。对于达到 2 °C 的路径，所有成本效益分析都为时已晚，但这种动态低效率对福利的影响要温和。同样，具有 overshoot 的 force 约束的分数最差。我们表明，本世纪末的大量负排放从来都不是最优的，而是超调的约束因素。