Net Social Benefits of Carbon Dioxide Removal: Carbon Cycle Feedbacks and Strategic Advantages (CDRecon)

为了保持将全球平均气温升幅控制在2摄氏度以下的机会，并限制长期气候变化，从大气中消除二氧化碳(二氧化碳清除)并将其处置在非大气碳库中变得越来越有必要。关于碳的社会成本的信息，即衡量向大气排放碳的成本，不足以评估CDR的社会效益，因为还需要考虑非大气碳库的社会成本。将碳移入陆地生物圈(例如通过植树造林)或海洋(例如通过在沿海地区传播橄榄石)的社会成本来自碳循环反馈和饱和效应，这意味着CDR的净社会效益低于节省的(大气)碳社会成本。本项目CDRecon通过将动态经济模拟和地球系统模拟相结合，开发了一种新的综合评估CDR的方法，以解决CDR非大气社会成本的两个问题：1)什么样的碳循环模型适合于综合评估CDR的净社会效益？2)什么是向CDR分配碳信用的合适方案？忽视非大气社会成本导致在气候政策中CDR措施的份额和时间方面的估计不一致。但无论如何，气候政策在现实中都是不完美的。非全球覆盖和不合作行为导致国际碳泄漏和搭便车。与减排和碳捕获与封存(CCS)不同，CDR允许从大气中消除扩散和过去的碳排放。因此，CDR在处理与不完善的气候政策相关的问题方面提供了一些尚未探索的战略优势。然而，如果在不考虑碳的非大气社会成本的情况下应用，它还可能增加另一个不完美的维度。CDRecon将使用并进一步发展综合评估模型(IAM)、敏感性分析、前瞻性可计算一般均衡(CGE)模型、微分博弈分析和(随机)动态优化方法，以解决气候政策中最优和非最优CDR的两个进一步问题：3)CDR如何影响全球协调的气候政策？4)CDRecon将如何影响国际碳泄漏和搭便车？CDRecon将同时研究最优和非最优CDR应用，后者是由于只关注大气社会成本而忽视碳循环反馈。

To maintain the chance of keeping the average global temperature increase below 2°C and to limit long-term climate change, removing carbon dioxide from the atmosphere (Carbon Dioxide Removal, CDR) and disposing of it in non-atmospheric carbon reservoirs is becoming increasingly necessary. Information on the social cost of carbon, i.e. measuring the cost of emitting carbon into the atmosphere, is not sufficient for assessing the social benefits of CDR because the social cost of non-atmospheric carbon reservoirs also needs to be taken into account. The social cost of removing carbon into the terrestrial biosphere (e.g., by afforestation) or the ocean (e.g. by spreading olivine in coastal areas) arises from carbon-cycle feedbacks and saturation effects, implying lower net social benefits of CDR than suggested by the saved (atmospheric) social cost of carbon. The present project, CDRecon, develops a new approach to an integrated assessment of CDR by combining dynamic economic modeling with earth system modeling to address two questions on Non-atmospheric Social Cost of CDR:1) What carbon cycle models are appropriate for integrated assessment of the net social benefits of CDR? 2) What is an appropriate scheme for assigning carbon credits to CDR? Neglecting non-atmospheric social cost results in inconsistent estimates with regard to the share and timing of CDR measures in climate policies. But climate policy is imperfect in reality anyway. Non-global coverage and non-cooperative behavior result in international carbon leakage and free-riding. In contrast to abatement and carbon capture and storage (CCS), CDR allows the removal of both, diffuse and past carbon emission from the atmosphere. Thus, CDR provides a number of unexplored strategic advantages in dealing with issues related to imperfect climate policies. Yet, if applied without accounting for the non-atmospheric social cost of carbon, it could also add a further dimension of imperfection. CDRecon will use and further develop methods of integrated assessment modeling (IAM), sensitivity analysis, forward-looking computable general equilibrium (CGE) models, differential game analysis, and (stochastic) dynamic optimization to address two further questions on Optimal and Non-optimal CDR in Climate Policies: 3) How is globally-coordinated climate policy affected by CDR?4) How is international carbon leakage and free-riding affected by CDR?CDRecon will study both, optimal and non-optimal CDR application, the latter arising from focusing only on the atmospheric social cost and neglecting carbon cycle feedbacks.