To achieve the goals of the Paris Agreement requires deep and rapid reductions in anthropogenic CO2 emissions, but uncertainty surrounds the magnitude and depth of reductions. Earth system models provide a means to quantify the link from emissions to global climate change. Using the concept of TCRE – the transient climate response to cumulative carbon emissions – we can estimate the remaining carbon budget to achieve 1.5 or 2 oC. But the uncertainty is large, and this hinders the usefulness of the concept. Uncertainty in carbon budgets associated with a given global temperature rise is determined by the physical Earth system, and therefore Earth system modelling has a clear and high priority remit to address and reduce this uncertainty. Here we explore multi-model carbon cycle simulations across three generations of Earth system models to quantitatively assess the sources of uncertainty which propagate through to TCRE. Our analysis brings new insights which will allow us to determine how we can better direct our research priorities in order to reduce this uncertainty. We emphasise that uses of carbon budget estimates must bear in mind the uncertainty stemming from the biogeophysical earth system, and we recommend specific areas where the carbon cycle research community needs to re-focus activity in order to try to reduce this uncertainty. We conclude that we should revise focus from the climate feedback on the carbon cycle to place more emphasis on CO2 as the main driver of carbon sinks and their long-term behaviour. Our proposed framework will enable multiple constraints on components of the carbon cycle to propagate to constraints on remaining carbon budgets.

中文翻译：

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量化过程级不确定性对 TCRE 和碳预算的贡献，以实现巴黎协定气候目标

为实现《巴黎协定》的目标，需要大幅度、快速地减少人为二氧化碳排放量，但减少的幅度和深度存在不确定性。地球系统模型提供了一种量化从排放到全球气候变化的联系的方法。使用 TCRE 的概念——对累积碳排放的瞬态气候响应——我们可以估计剩余的碳预算达到 1.5 或 2 oC。但不确定性很大，这阻碍了概念的实用性。与给定的全球温度上升相关的碳收支的不确定性是由地球物理系统决定的，因此地球系统建模具有明确和高度优先的职责来解决和减少这种不确定性。在这里，我们探索了跨三代地球系统模型的多模型碳循环模拟，以定量评估传播到 TCRE 的不确定性来源。我们的分析带来了新的见解，这将使我们能够确定如何更好地指导我们的研究重点，以减少这种不确定性。我们强调，碳预算估算的使用必须牢记源自生物地球物理地球系统的不确定性，我们建议碳循环研究界需要重新关注活动的特定领域，以尽量减少这种不确定性。我们得出的结论是，我们应该修改对碳循环的气候反馈的关注，更多地强调 CO2 作为碳汇及其长期行为的主要驱动力。