Global Systems Institute and Geography Department, University of Exeter, Exeter, UK.
College of Life and Environmental Sciences, University of Exeter, Penryn, Cornwall, UK.
Nat Commun. 2022 Aug 25;13(1):5008. doi: 10.1038/s41467-022-32653-x.
The cooling transition into the Little Ice Age was the last notable shift in the climate system prior to anthropogenic global warming. It is hypothesised that sea-ice to ocean feedbacks sustained an initial cooling into the Little Ice Age by weakening the subpolar gyre circulation; a system that has been proposed to exhibit bistability. Empirical evidence for bistability within this transition has however been lacking. Using statistical indicators of resilience in three annually-resolved bivalve proxy records from the North Icelandic shelf, we show that the subpolar North Atlantic climate system destabilised during two episodes prior to the Little Ice Age. This loss of resilience indicates reduced attraction to one stable state, and a system vulnerable to an abrupt transition. The two episodes preceded wider subpolar North Atlantic change, consistent with subpolar gyre destabilisation and the approach of a tipping point, potentially heralding the transition to Little Ice Age conditions.
进入小冰期的冷却期是人为全球变暖之前气候系统的最后一次显著变化。据推测,海冰与海洋的反馈通过削弱亚极地回旋流,维持了小冰期的初始冷却;有人提出该系统具有双稳性。然而,在这一转变中,双稳性的经验证据一直缺乏。利用来自冰岛北部大陆架的三个每年解析的双壳类代理记录中的恢复力统计指标,我们表明,在小冰期之前,亚极地北大西洋气候系统在两个时期发生了失稳。这种恢复力的丧失表明对一个稳定状态的吸引力降低,以及一个容易发生突然转变的系统。这两个时期先于更广泛的亚极地北大西洋变化,与亚极地回旋流的失稳和临界点的逼近一致,可能预示着向小冰期条件的转变。