Abstract Recent studies have found a significant mismatch between the amount of low-frequency variability in paleo-hydroclimate records and that simulated by climate models. However, uncertainties in how proxy systems record climate are significant, and the influence of low-frequency non-climate noise in paleoclimate archives is difficult to constrain. We use proxy system models to compare a network of mostly δ18O tree cellulose records from Monsoon Asia with isotope-enabled climate model output from (1) a coupled fully-forced version of iCESM (850–2005 CE), (2) isoGSM nudged toward the 20th Century Reanalysis (1871–2010 CE), and (3) an atmosphere-only run of iCAM5 with prescribed sea-surface temperatures from observations (1850–2014 CE). We identify a large discrepancy in scaling behavior between hydroclimate proxies and analogous iCESM pseudoproxies. In contrast, pseudoproxy networks based on climate models constrained by observations (isoGSM and iCAM5) have variance that continues to increase from decadal to multidecadal scales. This indicates that the mismatch arises from a failure of iCESM to simulate a sufficient amount of low-frequency hydroclimate variability. We test the influence of non-climate noise and photosynthate storage and find that they play a small role in elevating the low-frequency signal of proxies, but cannot explain the mismatch. Although our results are constrained to Monsoon Asia, the scaling of hydroclimate proxies across other regions and models have shown similar behavior, suggesting a proxy-model mismatch on a global scale that likely stems from an underestimation of low-frequency variability in fully coupled climate models.

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亚洲季风变率的频谱：水文气候尺度不匹配的代理系统模型方法

摘要 最近的研究发现古水文气候记录中的低频变异量与气候模型模拟的低频变异量之间存在显着的不匹配。然而，代理系统如何记录气候的不确定性很大，并且古气候档案中低频非气候噪声的影响难以约束。我们使用代理系统模型来比较来自亚洲季风的主要是 δ18O 树纤维素记录的网络与来自 (1) 耦合的完全强制版本的 iCESM (850–2005 CE)，(2) isoGSM 的同位素启用气候模型输出20 世纪再分析（1871-2010 CE），和（3）iCAM5 的仅大气运行，具有来自观测的规定海面温度（1850-2014 CE）。我们发现水文气候代理和类似的 iCESM 伪代理之间的缩放行为存在很大差异。相比之下，基于受观测约束的气候模型（isoGSM 和 iCAM5）的伪代理网络具有从十年到几十年尺度持续增加的方差。这表明不匹配是由于 iCESM 未能模拟足够数量的低频水文气候变化所致。我们测试了非气候噪声和光合储存量的影响，发现它们在提升代理低频信号方面的作用很小，但无法解释不匹配。尽管我们的结果仅限于亚洲季风，但其他地区和模型的水文气候代理的缩放也显示出类似的行为，