SWEET:Super-Warm Early Eocene Temperatures and climate: understanding the response of the Earth to high CO2 through integrated modelling and data

地球气候目前正在迅速变化，这主要是由于人类工业化造成的温室气体排放。预计到本世纪，这些排放量将增加，在某些情况下，到2100年，大气中二氧化碳(CO2)的浓度可能会达到百万分之1000以上，而工业化之前的浓度为280ppm。为了预测这些情景的社会、环境和经济影响，从而更好地为它们做好准备，我们可以使用的唯一工具是气候模型。为了评估我们对气候模型预测的信心，我们通常会在已知气候条件下对它们进行测试。然而，这项测试(以及相关的模型调整)几乎完全是在现代气候条件下进行的，而且是相对于最近观测到的气候变化进行的，在这些气候变化中，二氧化碳浓度低于400ppmv。因此，我们最先进的气候模型从未在高二氧化碳、超温气候条件下进行过测试，它们主要应用于这些气候条件，并在此基础上做出重大决策。然而，在地球更深的过去(例如约5000万年前的始新世)，存在着二氧化碳浓度与本世纪末预期的浓度相似的时间段；但这些时间段的气候学信息目前很少，而且与巨大的不确定性相关，二氧化碳的确切浓度鲜为人知。最近，我们对地质记录如何保存气候信号的理解发生了变化，以及实验室技术的发展，这意味着第一次有了一个新的令人兴奋的机会来纠正这种情况，并在一个超级温暖的世界中对我们最新的气候模型进行急需的评估。总之，我们将应用这些新兴技术，并开发新的方法和工具，以产生始新世温度的全球数据集。结合新的高保真的始新世二氧化碳浓度重建，以及最先进的古地理地图(大陆位置、山脉、海洋深度等)，我们将使用该数据集来测试在高大气二氧化碳、始新世条件下的最先进的气候模型。UKESM模型与英国气象局在国际CMIP6项目中使用的模型相同，该项目本身将是下一份政府间气候变化专门委员会(IPCC)评估报告的主要投入。我们还将使用我们的数据和额外的模型模拟(以高空间分辨率运行)来调查各种机制的相对重要性，这些机制决定了地球系统对高二氧化碳和古地理变化的响应。甜蜜的一个特点是，我们将充分考虑地质数据和建模中的不确定性，我们的模型数据比较将得到纳入这些不确定性的统计框架的支持。我们还将采用“多代理”方法，使用几个独立的地质档案来重建温度。对于其中的一个档案，即始新世微小海洋生物化石贝壳的氧同位素组成，我们将应用一种特别创新的方法，通过使用极细尺度的离子探测器来调查这些过去气候变化的同位素特征是如何记录在单个化石中的，从而使我们能够‘复活’以前不可信的数据。SWEET与英国气象局以及国际DeepMIP项目有着密切的联系，DeepMIP项目是‘古气候模拟国际比较项目’的一部分，该项目本身是CMIP6的一部分。我们预计，我们的结果将纳入下一份气专委评估报告，从而最终为政策提供参考。

The Earth's climate is currently changing rapidly, primarily due to emissions of greenhouse gases caused by human industrialisation. These emissions are projected to increase through this century, and under some scenarios atmospheric carbon dioxide (CO2) concentrations could reach more than 1000 parts per million (ppm) by the year 2100, compared with 280 ppm prior to industrialisation. In order to predict the sociological, environmental, and economic impacts of such scenarios, and thus to better prepare for them, the only tool at our disposal is climate modelling. In order to assess our confidence in predictions from climate models, they are routinely tested under conditions of known climate. However, this testing (and associated tuning of the models) is almost exclusively carried out under modern climate conditions, and relative to recently observed climate change, for which CO2 concentrations are less than 400 ppmv. As such, our state-of-the-art climate models have never been tested under the high CO2, super-warm climate conditions to which they are primarily applied, and upon which major policy decisions are made.However, there exist time periods in Earth's deeper past (for example the Eocene, about 50 million years ago) when CO2 concentrations were similar to those expected by the end of this century; but climatological information from these time periods is currently sparse and is associated with large uncertainties, and the exact concentrations of CO2 are only poorly known. Recent changes in our understanding of how the geological record preserves climate signals, and developments in laboratory techniques, mean that for the first time there exists a new and exciting opportunity to remedy this situation and provide a much-needed evaluation of our very latest climate models in a super-warm world.In SWEET, we will apply these emerging techniques, and develop new methodologies and tools, to produce a global dataset of Eocene temperatures. Coupled with new and high-fidelity reconstructions of Eocene CO2 concentrations, and state-of-the-art maps of the 'palaeogeograpy' (continental positions, mountain ranges, ocean depths etc.), we will use this dataset to test a state-of-the art climate model under high atmospheric CO2, Eocene conditions. The model, UKESM, is identical to that being used by the UK Met Office in the international 'CMIP6' project, which itself will be the primary input to the next Intergovernmental Panel on Climate Change (IPCC) assessment report. We will also use our data and additional model simulations (running at high spatial resolution) to investigate the relative importance of the various mechanisms which determine the response of the Earth system to high CO2 and to changes in palaeogeography.A characteristic of SWEET is that we will take full account of uncertainties in the geological data and the modelling, and our model-data comparisons will be underpinned by a statistical framework which incorporates these uncertainties. We will also adopt a 'multi-proxy' approach by using several independent geological archives to reconstruct temperature. For one of these archives, namely the oxygen isotopic composition of the fossilised shells of microscopic marine creatures from the Eocene, we will apply a particularly innovative approach which will enable us to 'resurrect' previously discredited data, by using an extremely fine-scale 'ion probe' to investigate how these isotopic signatures of past climate change are recorded in individual fossils.SWEET has strong links to UK Met Office, and to the international DeepMIP project, which is part of the 'Palaeoclimate Modelling Intercomparison Project', itself part of CMIP6. We expect our results to feed into the next IPCC assessment reports and therefore to ultimately inform policy.