Evaluating Emergent Constraints on Equilibrium Climate Sensitivity
Evaluating Emergent Constraints on Equilibrium Climate Sensitivity
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DOI：
10.1175/jcli-d-17-0631.1
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发表时间：
2018-05-01
影响因子：
4.9
通讯作者：
Klein, Stephen A.
中科院分区：
文献类型：
--
作者：
Caldwell, Peter M.;Zelinka, Mark D.;Klein, Stephen A.
紧急约束是从当前测量中可观察到的量，并且具有预测未来气候的技能。本研究探讨了19个先前提出的与平衡气候敏感性（ECS;全球平均平衡地表温度对CO2加倍的响应）相关的紧急约束。几个限制被证明是密切相关的，强调了仔细理解建议的限制的重要性。提出了一种新的方法，用于将紧急约束与ECS之间的相关性分解为与物理过程和地理区域相关的项。使用这种分解，可以确定是否与ECS相关的过程和区域解释对应的约束提供的物理解释。短波云反馈通常被认为是与ECS相关的主要贡献者，因为它是ECS中模型间传播的最大来源。在所有情况下，相关性的结果之间的相互作用的各种条款，反映了复杂的性质，ECS和反馈条款和强迫本身是相互关联的。对于19个约束中的4个，我们的分析证实了最初提出的相关性解释。这四个限制因素都预示着相对较高的气候敏感性。由于与ECS的相关性主要来自意想不到的来源和/或缺乏对合奏变化的鲁棒性，其他六个约束的可信度受到质疑。另外六个限制缺乏可检验的解释，因此无法确认。事实上，这项研究提出了更多的限制比它证实的怀疑，强调需要谨慎识别时，从小合奏紧急约束。
Emergent constraints are quantities that are observable from current measurements and have skill predicting future climate. This study explores 19 previously proposed emergent constraints related to equilibrium climate sensitivity (ECS; the global-average equilibrium surface temperature response to CO2 doubling). Several constraints are shown to be closely related, emphasizing the importance for careful understanding of proposed constraints. A new method is presented for decomposing correlation between an emergent constraint and ECS into terms related to physical processes and geographical regions. Using this decomposition, one can determine whether the processes and regions explaining correlation with ECS correspond to the physical explanation offered for the constraint. Shortwave cloud feedback is generally found to be the dominant contributor to correlations with ECS because it is the largest source of intermodel spread in ECS. In all cases, correlation results from interaction between a variety of terms, reflecting the complex nature of ECS and the fact that feedback terms and forcing are themselves correlated with each other. For 4 of the 19 constraints, the originally proposed explanation for correlation is borne out by our analysis. These four constraints all predict relatively high climate sensitivity. The credibility of six other constraints is called into question owing to correlation with ECS coming mainly from unexpected sources and/or lack of robustness to changes in ensembles. Another six constraints lack a testable explanation and hence cannot be confirmed. The fact that this study casts doubt upon more constraints than it confirms highlights the need for caution when identifying emergent constraints from small ensembles.