Cretaceous-Paleocene-Eocene: Exploring Climate and Climate Sensitivity

地球对大气中二氧化碳浓度升高的敏感度有多高？在过去的二十年里，这个关键的问题一直是深入研究的主题。最近，越来越多的人使用过去的气候来评估用于未来预测的模型，并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，但程度尚不清楚。在这项研究中，我们将使用一个模拟框架来探索古地理在白垩纪到始新世(145-3500万年前；145-35 Ma)最近的温室气候区间内控制气候和气候敏感性的作用。我们将调查与重建的古地理和使用的模型相关的不确定性。我们将通过将模型结果与现有数据的观察汇编进行比较来评估我们的发现，我们将综合和重新解释这些数据。这项工作将为我们的星球如何在长时间(数百万年)的时间尺度上运行提供令人着迷的见解，并评估对过去温暖气候的观测对未来气候敏感性的影响。使这项研究适时的三项最新发展是：(1)全新的白垩纪至始新世古地理地图，在精度和时间分辨率方面比以前的表示法有了很大改进，(2)可用计算能力的阶跃变化意味着我们第一次能够将大型气候模拟集合旋转到平衡，使我们能够探索不确定性，以及(3)对古气候指标控制和限制的新理解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.