Assessing the role of millennial-scale variability in glacial-interglacial climate change

地球气候的时间尺度从几十年到数千万年不等。曾经，这种变化模式与地球绕太阳轨道的变化有关。这就是众所周知的“轨道-时间尺度”变化，具有数万到数十万年的特征时间尺度，导致了众所周知的晚更新世冰川周期。在这种冰期-间冰期变异性的基础上，还有另一种气候变化模式，称为“千年尺度”气候变异性(以数百年至几千年的时间尺度变化为特征)。这两种气候变化模式都收到了重大的科学询问，因为它们涉及全球气候的重大变化，但两种模式的基本机制仍是谜。然而，最近的研究表明，这些表面上独立的机制实际上可能是密切相关的。因此，改善我们对其中一个的理解应该促进对另一个的理解。在这里，我们试图调查千年尺度的气候变异性在与冰川-间冰期气候变化相关的更广泛变化中的潜在作用。具体地说，我们将研究海洋/大气环流的突然变化所产生的影响，这些变化可能在从冰川气候向间冰期气候的转变中发挥作用(例如最后一次冰川消融，发生在2万到1万年前)。人们认为，海洋环流和相关大气现象的变化可以引起巨大的温度波动，就像格陵兰冰芯在最后一次冰川和去冰川时期记录到的那样。值得注意的是整个南极洲记录的相应温度变化，这表明气候系统可能像一种秋千；当环流很强时，格陵兰(和西北欧)温暖，南极洲变冷。环流减弱导致整个格陵兰地区寒冷，而整个南极洲则在变暖。这种所谓的“两极摇摆板”的一个重要副作用是，每当大气环流处于减弱状态时，大气中的二氧化碳似乎就会上升。与这一提议特别相关的是上一次冰川消融期间二氧化碳的上升，这与两极拉锯的明显振荡有关。此外，在最后一次冰期还发生了其他几次跷跷板振荡，这也导致了二氧化碳的增加，但没有导致冰川消融。我们希望找出为什么某些两极跷跷板振荡(末端振荡)明显导致冰川消融，而另一些(非末端振荡)则不会。这些事件有没有什么特别之处，或者它们与冰川消融的联系仅仅是巧合？为了回答这个问题，我们将把定量数据分析与最先进的气候系统计算机模型结合起来。我们将分析几个冰川周期的气候记录，以提供两极秋千的“末端”和“非末端”振荡的统计表示。然后，我们将使用计算机模型来研究在各种背景条件下秋千是如何运作的。我们的最终目标是找出是什么让终端振荡变得特别。在这样做的时候，我们将对冰川消融的机制提供重要的约束。

Earth's climate varies on timescales ranging from decades to tens of millions of years. Once such mode of variability is that related to changes in the Earth's orbit around the Sun. This is known as 'orbital-timescale' variability and has characteristic timescales of tens to hundreds of thousands of years, giving rise to the well known glacial cycles of the Late Pleistocene. Superimposed on this glacial-interglacial variability is another mode of climate change, known as 'millennial-scale' climate variability (characterised by changes on a timescale of hundreds to a few thousands of years). Both of these modes of climate variability have received significant scientific enquiry because they involve major changes in global climate and yet both remain enigmatic in their underlying mechanisms. However, recent studies have suggested that these apparently separate mechanisms may in fact be intimately related. As such, improving our understanding of one should promote understanding in the other. Here we seek to investigate the potential role of millennial-scale climate variability in the wider changes associated with glacial-interglacial climate change. Specifically we will examine the effects that occur in response to abrupt changes in ocean/atmosphere circulation that may play a role in the transition from glacial to interglacial climate (such as the last deglaciation, which occurred between 20 and 10 thousand years ago).It is thought that changes in ocean circulation and related atmospheric phenomena can give rise to dramatic temperature fluctuations such as those recorded by Greenland ice cores during the last glacial and deglacial periods. Of note is the corresponding temperature variations recorded across Antarctica, which suggest that the climate system may act like a sort of seesaw; when circulation is strong, Greenland (and north western Europe) is warm and Antarctica cools. A weakened circulation gives rise to cold conditions across Greenland while warming occurs across Antarctica. An important side effect of this so-called 'bipolar seesaw' is that atmospheric carbon dioxide appears to rise every time the circulation is in a weakened state. Of particular relevance to this proposal is the rise in carbon dioxide that occurred during the last deglaciation, which was associated with a distinct oscillation of the bipolar seesaw. Moreover, several other seesaw oscillations occurred during the last glacial period, which also gave rise to increases in carbon dioxide but did not lead to deglaciation.We wish to find out why certain bipolar seesaw oscillations (terminal oscillations) apparently lead to deglaciation while others (non-terminal oscillations) do not. Is there anything special about these events or is their affiliation with deglaciation merely coincidence? In order to answer to this question we will combine quantitative data analysis with state-of-the-art computer models of the climate system. We will analyse climate records spanning several glacial cycles in order to provide a statistical representation of 'terminal' and 'non-terminal' oscillations of the bipolar seesaw. We will then use computer models to investigate how the seesaw operates under a variety of background conditions. Our ultimate goal is to find out what, if anything, makes terminal oscillations special. In so doing we will provide important constraints on the mechanism of deglaciation.