Colloborative Research: Assessing Climate Model Simulations of Last Glacial Maximum Ocean Circulation with Carbon Isotopes

古气候学的关键前提之一是，了解过去的气候可以让我们深入了解当今和未来的气候。 一个推论是，气候模型能够忠实地模拟过去的气候，特别是在末次盛冰期（LGM；约2万年前）等极端时期，将有助于我们改进这些模型，并使我们对它们对未来气候变化的预测更有信心。在过去的几十年里，世界各地的科学家定期对过去几个世纪和未来气候的最新模型模拟进行相互比较。在其最新版本（政府间气候变化专门委员会第五次评估报告，或 IPCC AR5）中，该练习还包括对末次冰期期间的气候模拟（古气候模型比对项目 - 第 3 阶段，或 PMIP3）。该项目由哥伦比亚大学拉蒙特·多尔蒂地球观测站和俄勒冈州立大学的研究人员合作，其主要目标是评估 AR5 和 PMIP3 气候模型套件模拟现代和末次盛冰期全球海洋环流的能力。目标是评估用于预测未来气候变化的最先进模型，并有助于更好地了解末次盛冰期期间的气候和海洋环流。由于缺乏对过去气候的直接观测，之前的评估受到了阻碍。 幸运的是，海洋环流与二氧化碳和其他生物地球化学微量物质的相互作用在海洋沉积物中留下了化学特征，记录了该时期的气候和海洋环流。 不幸的是，虽然科学家已经非常擅长测量它们，但这些化学特征只是环境气候的间接和不精确的记录。为了解决这个问题，研究人员开发了一种能够直接模拟生物地球化学示踪剂及其与海洋环流相互作用的模型。结合一种新颖的计算技术，研究人员将在 AR5 和 PMIP3 模型中模拟这些示踪剂，然后将它们直接与沉积物中测量的化学特征进行比较。通过分析结果，研究人员将能够描述每个模型的循环特征，确定潜在的影响因素，并根据观察到的数据评估其性能。这项工作与正在进行的更准确地限制过去的气候、预测人类活动对气候系统的未来影响以及开发能够模拟不同气候状况的模型的努力高度相关。这项工作涉及与世界各地（德国、日本、法国和澳大利亚）的气候建模小组的合作。

One of the key premises in paleoclimatology is that understanding of past climate can give us insight into present day and future climate. A corollary is that the ability of climate models to faithfully simulate past climate, particularly during extreme periods such as the Last Glacial Maximum (LGM; ~20,000 years ago), will help us improve these models and give us more confidence in their projections of future climate change. Over the past few decades scientists around the world have periodically carried out an intercomparison of the latest model simulations of climate over the past few centuries and the future. In its most recent iteration (the Intergovernmental Panel of Climate Change Fifth Assessment Report, or IPCC AR5), this exercise also includes simulations of climate during the last glacial period (the Paleoclimate Model Intercomparison Project- Phase 3, or PMIP3). The primary goal of this project, a collaboration between researchers from Columbia University's Lamont Doherty Earth Observatory and Oregon State University, is to evaluate the ability of the AR5 and PMIP3 suite of climate models to simulate the modern and LGM global ocean circulation. The goal is to both assess the state-of-the-art models used to project future climate change, as well as to contribute to a better understanding of climate and ocean circulation during the LGM. Previous assessments have been hampered by the lack of direct observations of past climates. Fortunately, the interaction of ocean circulation with carbon dioxide and other biogeochemical trace material leaves behind chemical signatures in ocean sediments that record the climate and ocean circulation of that period. Unfortunately, while scientists have become quite adept at measuring them, these chemical signatures are only indirect and imprecise recorders of ambient climate. To get around this problem, the researchers have developed a model capable of directly simulating biogeochemical tracers and their interaction with ocean circulation. Coupled with a novel computational technique, the researchers will simulate these tracers in the AR5 and PMIP3 models, and then compare them directly to the chemical signatures measured in sediments. By analyzing the results the researchers will be able to characterize the circulation of each model, identify the underlying factors responsible, and assess its performance against observed data. The work is highly relevant to ongoing efforts to more accurately constrain past climates, to project the future impact of human activity on the climate system, and to develop models capable of simulating different climate regimes. The work involves collaboration with climate modeling groups around the world (Germany, Japan, France, and Australia).