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？过去二十年来，这个关键问题一直是深入研究的主题。最近，越来越多地利用过去的气候来评估用于未来预测的模式，并提供对气候敏感性的观测约束。然而，过去气候对未来敏感性的相关性还有待检验。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，但影响的程度是未知的。在这项研究中，我们将使用一个建模框架来探索从白垩纪到始新世（1.45亿至~ 3500万年前；145-35 Ma）最近的“温室”气候期间，古地理在控制气候和气候敏感性方面的作用。我们将研究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——我们将综合并重新解释现有数据的汇编。这项工作将为我们的星球在长期（数百万年）的时间尺度上如何运行提供有趣的见解，并评估过去温暖气候观测的效用，为未来的气候敏感性提供信息。最近的三个发展使这项研究变得及时：(1)白垩纪至始新世的全新古地理地图，在精度和时间分辨率方面都大大提高了以前的表现；(2)可用计算能力的阶跃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)对古气候代用物的控制和限制的新认识意味着我们可以将我们的模式模拟与地质记录进行最先进的比较。

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.