Quantifying variability of the El Nino Southern Oscillation on adaptation-relevant time scales using a novel palaeodata-modelling approach

这里提出的研究旨在帮助我们了解世界各地气候的年际变化。这包括洪水和干旱、热浪和寒流的发生。为此，我们将研究地球上气候年际变化的最大来源，即厄尔尼诺现象。厄尔尼诺现象是一种温暖的洋流，每隔3-5年在南美洲西北部海岸出现一次，它是一个更大范围现象的结果，涉及整个热带太平洋的风、降雨量、温度和洋流的变化。更大范围的现象被称为厄尔尼诺南方涛动，这个名字反映了这样一个事实，即它涉及大气和表层海洋的循环及其相互作用的自然循环。虽然我们知道ENSO起源于热带太平洋，但它的影响几乎遍及全球，因为它影响了大气环流，从而影响了风和水汽从热带到热带外的输送。洪水和干旱以及厄尔尼诺带来的暴风雨的发生变化直接影响到10多亿人的生活和生计，重大厄尔尼诺事件导致数万人死亡，数十亿英镑的损失，以及对珊瑚礁等一些自然生态系统的破坏。甚至欧洲也经历了与ENSO相关的天气模式的变化！虽然我们现在对ENSO循环背后的基本机制有了很好的了解，但一些主要问题仍然存在。特别是，我们不明白为什么一些厄尔尼诺事件比另一些强得多，为什么有些几十年的厄尔尼诺活动要强得多，或者ENSO将如何应对气候变化。为了帮助回答其中的一些问题，我们将通过分析生活在加拉帕戈斯群岛的老死(化石)珊瑚骨骼中的生长环，重建过去5000年来ENSO的变化。加拉帕戈斯群岛经历了与厄尔尼诺现象相关的极端天气变化(在事件期间变得更温暖和更潮湿)，这些变化记录在生活在周围海洋的珊瑚骨骼的化学中。其中一些珊瑚的寿命长达一百年，甚至更长，形成了一层又一层的骨骼，有点像树轮。我们将通过古老的死亡珊瑚收集岩心，包括一些生活在数千年前的珊瑚。然后，通过分析珊瑚生长带的化学成分，我们将能够重建珊瑚在其一生中经历的气候和ENSO的变化。通过结合许多这类珊瑚的记录，我们将建立一幅关于ENSO自然变化的图景，帮助我们了解重大事件发生的频率，以及ENSO发生了多少十年至十年的变化。这些珊瑚记录可以让我们重建ENSO过去变化的历史，但它们本身并不能帮助我们了解这些变化的原因。它们是由太阳辐射的变化引起的吗？或者是由于重大火山喷发的降温效应？或者它们只是我们应该预料到的随机变化，而不是任何形式的触发？要回答这些问题，我们需要使用气候模型。我们现在用来预测未来气候的模型也可以用来研究ENSO的变化。在我们的工作中，我们将使用最新的气候模型，看看它们是否能正确地复制我们的珊瑚记录所定义的过去几千年来观察到的ENSO变化。我们还可以在这些模型中看到火山喷发、太阳辐射和温室气体变化的影响。通过将模式结果与珊瑚记录进行比较，我们将更好地了解ENSO变化的性质和原因，以及模式预测这一变化的技巧。通过这种方式，我们将在帮助预测未来几十年与ENSO相关的气候事件的可能范围方面做出重大贡献。

The research proposed here aims to help us understand year-to-year variations in climate around the world. This includes the occurrence of floods and droughts, of heat waves and cold spells. To do this, we are going to examine the largest source of year-to-year climate variability on Earth, namely, El Niño. The El Niño is a warm ocean current that appears off the coast of NW South America every 3-5 years, and it is a result of a much larger scale phenomenon involving changes to the winds, rainfall, temperature and ocean currents across the whole of the tropical Pacific. The larger scale phenomenon is known as the El Niño Southern Oscillation, a name which reflects the fact that it involves a natural cycle in the circulation of both the atmosphere and the surface ocean and how they interact. Although we know that ENSO originates in the tropical Pacific, it has near world-wide impacts because of the way it affects the circulation of the atmosphere, and hence the winds and transport of moisture from the tropics to the extra-tropics. Floods and droughts and changed incidence of storminess from El Niño directly affect the lives and livelihoods of well over a billion people, and major El Niño events are associated with tens of thousands of human deaths, billions of pounds of damage, and devastation to some natural ecosystems such as coral reefs. Even Europe experiences changed weather patterns associated with ENSO! Although we now understand quite well the basic mechanisms behind the ENSO cycle, some major questions remain. In particular, we do not understand why some El Niño events are much stronger than others, why some decades show much stronger El Niño activity, or how ENSO will respond to climate change. To help answer some of these questions, we will reconstruct changes in ENSO over the past 5,000 years by analysing growth rings in the skeletons of old dead ('fossil') corals that lived in the Galápagos. The Galápagos Islands experience extreme changes in weather associated with El Niño (warmer and wetter during events), and these changes are recorded in the chemistry of the skeletons of corals living in the surrounding ocean. Some of these corals live for up to a hundred years, or longer, laying down layers of skeleton a bit like tree rings. We will collect cores through old dead corals, including some that lived thousands of years ago. Then, by analysing the chemistry of their growth bands we will be able to reconstruct the changes in climate, and ENSO, that the corals experienced during their life time. By combining the records from many such corals we will build up a picture of the natural variability in ENSO, helping us see how often major events occurred, and how much decade-to-decade variability in ENSO occurred. These coral records can let us reconstruct the history of past changes in ENSO, but on their own they do not help us to understand the causes of the changes. Were they due to changes in the sun's radiation? Or due to the cooling effects of major volcanic eruptions? Or were they simply random variations that we should expect without any sort of trigger? To answer these questions, we need to use climate models. The same models that we now use to predict future climate can be used to research changes in ENSO. In our work, we will use the most up-to-date climate models to see if they can correctly replicate the observed changes in ENSO over the past few thousand years as defined by our coral records. We can also see what the effects are of changing volcanic eruptions, solar radiation and greenhouse gases in these models. By comparing the model results with the coral records we will get a better understanding of the nature and causes of changes in ENSO, and the skill of the models at predicting this. In this way we will make a significant contribution to helping predict the likely range of ENSO-related climate events for the coming decades.