NERC - NSFGEO: Pliocene Lessons for the Indian Ocean Dipole (PLIOD)

印度洋的气候模式影响着超过10亿人的淡水供应。例如，印度季风的巨大变化，无论是干旱还是极端降雨，都可能导致作物歉收，并对依赖季风降雨的社会造成巨大危害。由于目前和未来人类造成的气候变化，我们预测所谓“变幻莫测”的印度季风会发生什么情况的能力面临挑战，因为历史数据有限，而且目前用于未来气候预测的计算机气候模型表现不佳[联合国政府间气候变化专门委员会第六次评估报告]。在未来气候变化情景下，气候模式模拟已经假设气候极端事件会增加，但还需要进一步的研究来证实潜在的过程和机制。将过去气候的地质重建与气候模型模拟结合起来，将有助于我们了解在全球气候变化下驱动印度洋的潜在气候动力学。2万年前，当极地地区有大片冰盖时，地质证据表明，由于印度尼西亚和澳大利亚周围的陆地暴露，印度洋出现了大规模的极端气候。这表明印度洋有能力转变为一种与今天根本不同的气候状态。然而，我们需要了解这种情况是否会在全球温暖气候下发生，并确定可能与全球寒冷气候不同的潜在机制。上新世中期的暖期（约300万年前）被用作未来气候变化的伪模拟，因为当时全球气温比现代高约3摄氏度，大气中的二氧化碳浓度与我们今天的升高水平相似。它是IPCC关于气候变化的古视角报告（上新世模式比较项目- PlioMIP）和古数据汇编（PAGES工作组PlioVAR和美国地质调查局PRISM）的关键气候模拟目标。在这个项目中，我们将使用最先进的地球化学技术和最先进的气候模型[英国地球系统模型（UKESM1）]来重建上新世中期暖期的气候。我们将重建过去300万年来印度洋的长期气候演变，并使用新的统计方法估计气候极端。我们提出了一系列气候模式模拟，将测试高大气温室气体水平和改变的陆地质量分布的影响。我们提出的重建将为预测平均气候条件和极端气候的未来变化的现实性提供一个变革性的过去气候视角。我们的结果将提高我们对IPCC未来报告中印度洋气候预测的信心。这项拟议的工作将推动我们对印度洋对全球气候系统的贡献的理解，并将使政策制定者受益，并有助于建立适应未来气候变化的社区。

Climate patterns in the Indian Ocean impact freshwater availability for over a billion people. For example, large variability in the Indian Monsoon, either drought or extreme rain, can cause crop failure and massive harm to societies that rely on monsoon rains. With ongoing and future human-caused climate change, our ability to predict what will happen with the so-called 'vagaries' of the Indian Monsoon is challenging due to limited historical data and poor performance of current computer climate models for future climate projections [United Nations Intergovernmental Panel on Climate Change Sixth Assessment Report]. Increased climate extremes have been hypothesised via climate model simulations under future climate change scenarios, but additional research is necessary to ground-truth the underlying processes and mechanisms. Using geological reconstructions of past climate together with climate model simulations will help us understand the underlying climate dynamics that drive the Indian Ocean under global climate change. Geologic evidence from 20,000 years ago, when the polar regions had large ice sheets, suggests the Indian Ocean had large climate extremes due to exposure of land mass around Indonesia and Australia. This shows the Indian Ocean is capable of switching to a climate state fundamentally different from today. However, we need to understand if this can happen during globally warm climates and identify the underlying mechanisms which may be different than globally cold climates. The mid-Pliocene warm period (~3 million years ago) is used as a pseudo-analog for future climate change because global temperatures were ~3oC higher than modern and atmospheric carbon dioxide concentrations were similar to our present day elevated levels. It is a key climate modeling target in the IPCC reports paleo-perspectives on climate change (Pliocene Model Intercomparison Project - PlioMIP) and paleo-data compilations (PAGES Working Group PlioVAR and United States Geological Survey PRISM). In this project, we will use state-of-the-art geochemical techniques and cutting-edge climate modeling [United Kingdom Earth System Model (UKESM1)] to reconstruct climate during the mid-Pliocene warm period. We will reconstruct the long-term climate evolution of the Indian Ocean over the last three million years and estimate climate extremity using novel statistical approaches. We propose a series of climate model simulations that will test the influence of high atmospheric greenhouse gas levels and altered land mass distribution. Our proposed reconstructions will provide a transformative past climate perspective on the realism of projected future changes of the both average climate conditions and climate extremes. Our results would improve our confidence in future climate projections of Indian Ocean climate in future IPCC reports. This proposed work will push the frontiers of our understanding of the Indian Ocean's contribution to the global climate system and will benefit policy makers and aid in building communities resilient to future climate change.