Reply to: Non-trivial role of internal climate feedback on interglacial temperature evolution
Reply to: Non-trivial role of internal climate feedback on interglacial temperature evolution
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回复：内部气候反馈对间冰期温度演化的重要作用
DOI：
10.1038/s41586-021-03931-3
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发表时间：
2021
期刊：
影响因子：
64.8
通讯作者：
Zeng, Cheng
中科院分区：
文献类型：
--
作者：
Bova, Samantha;Rosenthal, Yair;Liu, Zhengyu;Yan, Mi;Broccoli, Anthony J.;Godad, Shital P.;Zeng, Cheng
量化代用重建中的季节性偏差（例如，海面温度（SST））一直是一个长期存在的挑战，阻碍了我们对过去气候演变的理解（例如，全新世温度难题）1，2。最近，Bova等人提出了一种季节到平均年转换（SAT）的方法，似乎可以有效地去除由季节日照变化引起的SST信号。为了提取全新世时期（距今1.2 - 1万年）的平均年SST（MASST）变化，Bova等人3选择了额外覆盖末次间冰期（LIG;距今1.28 - 1.15万年）的SST记录，假定SST仅归因于当地太阳辐射的变化，因此可以可靠地量化SST记录中的季节性偏差。然而，这一假设从根本上是不正确的，因为它忽略了地球内部系统反馈（例如海冰）对LIG温度变化的作用，这表明他们的研究结果实际上是有偏差的，过度校正了SST代理中的太阳辐射引起的季节性偏差。我们同意，全球冰量和温室气体浓度在LIG期间相对稳定（图1a，B），与季节性日照变化相比，它们对季节性未经调整的SST（SSTsn）变化的直接贡献可能微不足道。然而，这并不意味着当代系统的内部反馈也有微不足道的作用。在各种内部反馈（例如，海冰，云，植被等）中，海冰是LIG的一个代表性例子，因为它经历了重建4，5和气候模式5-7所建议的显着的当代进步。海冰对温度的反馈是一种公认的有效的正反馈。最近，England等人8在当今气候背景下，采用代表性浓度路径8.5海冰覆盖率（包括南大洋约35%的冬季海冰损失和北极约70%的夏季海冰损失（常年海冰残留持续存在））进行了一项敏感性实验。他们发现，极地海冰的减少可以直接导致热带MASST增加0.6 C以上（图2）。特别是，Bova等人3中使用的所有核心位置的特征都是年平均变暖，幅度在0.4和1 C之间。（128-125 kyr bp），两个极地地区都经历了显著的海冰损失4，5（例如，南极冬季海冰可能已经消退了高达65%（参考文献6），北极可能出现夏季无海冰的情况7），这比参考文献8中规定的要多。在此之后，海冰体积显著增加（注意，它们的驱动机制可能不同-前者主要是由海冰引起的年平均日射量驱动
Quantifying seasonal bias in proxy reconstructions (for example, sea surface temperature (SST)) has been a long-standing challenge, hampering our understanding of past climate evolution (for example, the Holocene temperature conundrum) 1, 2. Recently, Bova et al. 3 proposed a seasonal to mean annual transformation (SAT) method that seems to effectively remove SST signal caused by seasonal insolation change. To extract mean annual SST (MASST) change for the Holocene epoch (12–0 thousand years before present (kyr bp)), Bova et al. 3 selected SST records that additionally cover the last interglacial (LIG; 128–115 kyr bp) period, for which SST is assumed to be solely attributed to variations in local solar insolation, hence allowing for reliable quantification of seasonal bias in SST records. However, this assumption is fundamentally incorrect because it overlooks the roles of internal Earth system feedback (for example, sea ice) on LIG temperature change, indicating that their findings are effectively biased by overcorrecting insolation-induced seasonal bias in SST proxies. We agree that global ice volume and greenhouse gas concentrations were relatively stable during the LIG (Fig. 1a, b) and their direct contributions to seasonally unadjusted SST (SSTsn) changes might be trivial, in comparison to the seasonal insolation change. However, this does not mean that contemporary internal feedbacks of the system also have a trivial role. Among various internal feedbacks (for example, sea ice, cloud, vegetation and so on), sea ice is one representative example for the LIG because it experienced significant contemporary advances as suggested by reconstructions 4, 5 and climate models 5–7. Sea ice–albedo feedback is a well-acknowledged effectively positive feedback on temperature changes. Recently, England et al. 8 conducted a sensitivity experiment applying a Representative Concentration Pathway 8.5 sea-ice scenario—including an approximately 35% winter sea-ice loss in the Southern Ocean and an approximately 70% summer sea-ice loss in the Arctic (perennial sea-ice remnants persist)—under an otherwise present-day climate background. They found that the polar sea-ice loss can directly cause an increase of tropical MASST by more than 0.6 C (Fig. 2). In particular, all of the core locations used in Bova et al. 3 are characterized by mean annual warming with magnitudes in a range between 0.4 and 1 C.During the peak warm period of the LIG (128–125 kyr bp), both polar regions experienced significant sea-ice losses 4, 5 (for example, Antarctic winter sea ice may have retreated by up to 65%(ref. 6) and a summer sea-ice-free condition probably happened in the Arctic 7) that were more than those imposed in ref. 8. Following that, sea-ice volume increased markedly (note that their driving mechanisms might be different—the former is mainly driven by obliquity-induced mean annual insolation