The UN Paris Agreement puts in place a legally binding mechanism to increase mitigation action over time. Countries put forward pledges called nationally determined contributions (NDC) whose impact is assessed in global stocktaking exercises. Subsequently, actions can then be strengthened in light of the Paris climate objective: limiting global mean temperature increase to well below 2 °C and pursuing efforts to limit it further to 1.5 °C. However, pledged actions are currently described ambiguously and this complicates the global stocktaking exercise. Here, we systematically explore possible interpretations of NDC assumptions, and show that this results in estimated emissions for 2030 ranging from 47 to 63 GtCO2e yr−1. We show that this uncertainty has critical implications for the feasibility and cost to limit warming well below 2 °C and further to 1.5 °C. Countries are currently working towards clarifying the modalities of future NDCs. We identify salient avenues to reduce the overall uncertainty by about 10 percentage points through simple, technical clarifications regarding energy accounting rules. Remaining uncertainties depend to a large extent on politically valid choices about how NDCs are expressed, and therefore raise the importance of a thorough and robust process that keeps track of where emissions are heading over time.
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机译：《联合国巴黎协定》建立了具有法律约束力的机制，以随着时间的推移增加缓解行动。各国提出了称为国家自主贡献（NDC）的承诺，其影响在全球盘点活动中进行评估。随后，可以根据巴黎的气候目标加强行动：将全球平均温度上升限制在2°C以下，并努力将其进一步限制在1.5°C以下。但是，目前对承诺的行动进行了模糊的描述，这使全球清点工作变得复杂。在这里，我们系统地探索了NDC假设的可能解释，并表明这导致2030年的估计排放量为47至63 GtCO2e yr -1 。我们表明，这种不确定性对于将升温限制在远低于2 C并进一步升高至1.5 C的可行性和成本有着至关重要的意义。各国目前正在努力澄清未来的国家数据中心的方式。我们通过简单的有关能源核算规则的技术澄清，确定了将总体不确定性降低约10个百分点的显着途径。剩下的不确定性在很大程度上取决于有关如何表达国家自主贡献的政治上有效的选择，因此，提高了透彻，稳健的过程的重要性，该过程可以跟踪排放随时间的流逝。
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