Cretaceous-Paleocene-Eocene: Exploring Climate and Climate Sensitivity

地球对大气中二氧化碳浓度的增加有多敏感？这一关键问题在过去二十年中一直是深入研究的主题。最近，人们越来越多地利用过去的气候，既评估用于未来预测的模型，又提供对气候敏感性的观测约束。然而，过去气候与未来敏感性的相关性尚待检验。特别是，不同的古地理（即大陆位置、山脉范围和高度以及海底深度）将影响气候和气候敏感性，但影响程度尚不清楚。在这项研究中，我们将使用一个建模框架来探索古地理学在控制气候和气候敏感性的作用，在最近的时间间隔的“温室”气候从白垩纪到始新世（145 〜 35百万年前; 145-35马）。我们将调查与重建的古地理和使用的模型有关的不确定性。我们将通过将模型结果与观测结果进行比较来评估我们的发现-我们将综合和重新解释现有数据的汇编。这项工作将为我们的地球如何在长时间（数百万年）的时间尺度上运行提供迷人的见解，并评估过去温暖气候的观测结果对未来气候敏感性的影响。最近的三个事态发展使这项研究及时：（1）全新的白垩纪至始新世古地理地图，在准确性和时间分辨率方面大大提高了以前的表现，（2）可用计算能力的一个步骤变化意味着我们第一次可以将模拟气候的大型集合旋转到平衡状态，使我们能够探索不确定性，（3）对古气候代用指标的控制和限制的新认识意味着我们可以提供我们的模型模拟与地质记录的最先进的比较。

How sensitive is the planet to increasing concentrations of atmospheric carbon dioxide? This crucial question has been the subject of intensive research over the past two decades. Recently, increasing use is being made of past climates, both to evaluate models used for future prediction, and to provide observational constraints on climate sensitivity. However, the relevance of past climates for future sensitivity is yet to be tested. In particular, differing palaeogeography (i.e. continental positions, mountain extents and height, and ocean floor depth) will influence climate and climate sensitivity, but to an extent that is unknown. In this study, we will use a modelling framework to explore the role of palaeogeography in controlling climate and climate sensitivity during the most recent interval of 'greenhouse' climates from the Cretaceous to Eocene (145 to ~35 million years ago; 145-35 Ma). We will investigate uncertainties related to the reconstructed palaeogeographies and the models used. We will evaluate our findings by comparing the model results with observations - compilations of existing data which we will synthesise and re-interpret. The work will provide fascinating insights into how our planet operates on long (multi-million year) timescales, and assess the utility of observations of past warm climates for informing future climate sensitivity. Three recent developments which make this study timely are: (1) Brand new palaeogeographic maps of the Cretaceous to Eocene which improve greatly on previous representations in terms of both accuracy and temporal resolution, (2) A step change in the computing power available means that for the first time we can spin up large ensembles of simulations climates to equilibrium, allowing us to explore uncertainties, and (3) New understanding of the controls and limitations on palaeoclimate proxies means that we can provide a state-of-the-art comparison of our model simulations with the geological record.