Climate Sensitivity Increases Under Higher CO2 Levels Due to Feedback Temperature Dependence
Climate Sensitivity Increases Under Higher CO2 Levels Due to Feedback Temperature Dependence
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DOI：
10.1029/2020gl089074
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发表时间：
2021-02-28
影响因子：
5.2
通讯作者：
Gregory, Jonathan M.
中科院分区：
文献类型：
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作者：
Bloch-Johnson, Jonah;Rugenstein, Maria;Gregory, Jonathan M.
14 个耦合大气环流模型中的 13 个模型中，平衡气候敏感性（二氧化碳加倍时的平衡变暖）随着二氧化碳浓度的增加而增加，为工业化前浓度的 0.5-8 倍。特别是，突然的 4 x CO2 平衡变暖是 2 x CO2 平衡变暖的两倍多。我们确定了三个潜在原因：非对数强迫、反馈二氧化碳依赖性和反馈温度依赖性。反馈温度依赖性解释了至少一半的灵敏度增加，而反馈二氧化碳依赖性解释了较小的份额，非对数强迫在许多模型中降低了灵敏度，因为它增加了灵敏度。 14 个模型中有 10 个模型的反馈温度依赖性为正，这主要是由于长波晴空反馈，而云反馈则导致灵敏度大幅提高。反馈温度依赖性会增加极端或失控升温的风险，并且估计会导致 6 个模型在 8 x CO2 下升温至少 3K。
Equilibrium climate sensitivity-the equilibrium warming per CO2 doubling-increases with CO2 concentration for 13 of 14 coupled general circulation models for 0.5-8 times the preindustrial concentration. In particular, the abrupt 4 x CO2 equilibrium warming is more than twice the 2 x CO2 warming. We identify three potential causes: nonlogarithmic forcing, feedback CO2 dependence, and feedback temperature dependence. Feedback temperature dependence explains at least half of the sensitivity increase, while feedback CO2 dependence explains a smaller share, and nonlogarithmic forcing decreases sensitivity in as many models as it increases it. Feedback temperature dependence is positive for 10 out of 14 models, primarily due to the longwave clear-sky feedback, while cloud feedbacks drive particularly large sensitivity increases. Feedback temperature dependence increases the risk of extreme or runaway warming, and is estimated to cause six models to warm at least an additional 3K under 8 x CO2.