Abstract. This article presents the results of a bifurcation analysis of a simple energy balance model (EBM) for the future climate of the Earth. The main focus is on the following question: can the nonlinear processes intrinsic to atmospheric physics, including natural positive feedback mechanisms, cause a mathematical bifurcation of the climate state, as a consequence of continued anthropogenic forcing by rising greenhouse gas emissions? Our analysis shows that such a bifurcation could cause an abrupt change to a drastically different climate state in the EBM, which is warmer and more equable than any climate existing on Earth since the Pliocene epoch. In previous papers, with this EBM adapted to paleoclimate conditions, it was shown to exhibit saddle-node and cusp bifurcations, as well as hysteresis. The EBM was validated by the agreement of its predicted bifurcations with the abrupt climate changes that are known to have occurred in the paleoclimate record, in the Antarctic at the Eocene–Oligocene transition (EOT) and in the Arctic at the Pliocene–Paleocene transition (PPT). In this paper, the EBM is adapted to fit Anthropocene climate conditions, with emphasis on the Arctic and Antarctic climates. The four Representative Concentration Pathways (RCP) considered by the IPCC (Intergovernmental Panel on Climate Change) are used to model future CO2 concentrations, corresponding to different scenarios of anthropogenic activity. In addition, the EBM investigates four naturally occurring nonlinear feedback processes which magnify the warming that would be caused by anthropogenic CO2 emissions alone. These four feedback mechanisms are ice–albedo feedback, water vapour feedback, ocean heat transport feedback, and atmospheric heat transport feedback. The EBM predicts that a bifurcation resulting in a catastrophic climate change, to a pre-Pliocene-like climate state, will occur in coming centuries for an RCP with unabated anthropogenic forcing, amplified by these positive feedbacks. However, the EBM also predicts that appropriate reductions in carbon emissions may limit climate change to a more tolerable continuation of what is observed today. The globally averaged version of this EBM has an equilibrium climate sensitivity (ECS) of 4.34 K, near the high end of the likely range reported by the IPCC.

中文翻译：

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人类世气候分岔

摘要。本文介绍了对地球未来气候的简单能量平衡模型 (EBM) 进行分叉分析的结果。主要关注以下问题：大气物理学固有的非线性过程，包括自然正反馈机制，是否会导致气候状态的数学分叉，这是由于温室气体排放不断增加而造成的持续人为强迫的结果？我们的分析表明，这种分叉可能会导致 EBM 中气候状态的突然变化，这种状态比上新世以来地球上存在的任何气候都更温暖、更平等。在以前的论文中，这种适应于古气候条件的 EBM 显示出鞍状节点和尖头分叉，以及滞后。EBM 通过其预测的分岔与已知发生在古气候记录、始新世-渐新世过渡（EOT）的南极和上新世-古新世过渡的北极的气候突变的一致性得到验证。 PPT）。在本文中，EBM 适合人类世气候条件，重点是北极和南极气候。IPCC（政府间气候变化专门委员会）考虑的四个代表性浓度路径 (RCP) 用于模拟未来的 CO2 浓度，对应于不同的人为活动情景。此外，EBM 调查了四个自然发生的非线性反馈过程，这些过程放大了仅由人为二氧化碳排放引起的变暖。这四种反馈机制是冰-反照率反馈、水汽反馈、海洋热传输反馈和大气热传输反馈。EBM 预测，在未来几个世纪内，人为强迫未减弱的 RCP 将发生分叉，导致灾难性的气候变化，转变为类似上新世前的气候状态，并被这些正反馈放大。然而，EBM 还预测，适当减少碳排放可能会将气候变化限制在今天观察到的更可容忍的范围内。该 EBM 的全球平均版本具有 4.34 K 的平衡气候敏感性 (ECS)，接近 IPCC 报告的可能范围的高端。EBM 预测，在未来几个世纪内，人为强迫未减弱的 RCP 将发生分叉，导致灾难性的气候变化，转变为类似上新世前的气候状态，并被这些正反馈放大。然而，EBM 还预测，适当减少碳排放可能会将气候变化限制在今天观察到的更可容忍的范围内。该 EBM 的全球平均版本具有 4.34 K 的平衡气候敏感性 (ECS)，接近 IPCC 报告的可能范围的高端。EBM 预测，在未来几个世纪内，人为强迫未减弱的 RCP 将发生分叉，导致灾难性的气候变化，转变为类似上新世前的气候状态，并被这些正反馈放大。然而，EBM 还预测，适当减少碳排放可能会将气候变化限制在今天观察到的更可容忍的范围内。该 EBM 的全球平均版本具有 4.34 K 的平衡气候敏感性 (ECS)，接近 IPCC 报告的可能范围的高端。EBM 还预测，适当减少碳排放可能会将气候变化限制在今天观察到的更可容忍的范围内。该 EBM 的全球平均版本具有 4.34 K 的平衡气候敏感性 (ECS)，接近 IPCC 报告的可能范围的高端。EBM 还预测，适当减少碳排放可能会将气候变化限制在今天观察到的更可容忍的范围内。该 EBM 的全球平均版本具有 4.34 K 的平衡气候敏感性 (ECS)，接近 IPCC 报告的可能范围的高端。