PaleoGradPhan: Paleoclimate meridional and zonal Gradients in the Phanerozoic

今天地球的温度并不是到处都是均匀的，但是，一般来说，赤道附近最热，两极最冷（“纬向温度梯度”），从西到东变化，例如热带西太平洋的沃茨比热带东太平洋的更热（“纬向温度梯度”）。这些梯度是气候系统的一个基本属性-例如，受大气和海洋环流、水蒸气、云和海冰的控制。温度梯度对于理解反馈的作用也很重要（如冰和气候之间的相互作用），以及对确定许多陆地表面特性、环境和生态的分布很重要。这些现代温度梯度的主要原因相对较好地理解;然而，当我们回到数百万年前的地球历史时，对温度梯度的知识和理解迅速减少。关于过去温度梯度的知识主要来自地质记录--从化石等间接来源对温度的估计。对控制过去梯度的物理机制的理解主要来自气候模型，这些模型可以配置为在过去的时间间隔内运行，并且可以询问其结果以确定过去梯度变化的原因。然而，对过去梯度的估计仅限于一些经过详细研究的时间“快照”，许多模型的结果与这些时间段的地质记录不一致。由于温度梯度是气候系统的一个基本属性，如果没有对过去的梯度的可靠知识和理解，我们就不能开始声称了解我们星球的气候历史--这是一个头等大事。最近的几项发展意味着我们现在能够在这个“重大挑战”问题上取得实质性进展。首先，最近地质学界一直在推动整理、质量控制，并提供过去5亿年来过去温度的广泛数据库。该数据库为重建随时间变化的温度梯度提供了理想的来源。其次，最近我们一直在开发英国气象局气候模型的一个版本，该模型可以产生与地质记录一致的温度梯度，并在经过研究的时间内选择快照，并且可以在超级计算机上运行足够快，以便我们进行所需数量的模拟。因此，有了这些新的工具，我们是研究这一问题的理想场所，特别是在这个拟议的项目中，我们将分析新的数据库，以重建整个中生代的温度梯度，在同一时期进行新的气候模型模拟，并利用温度数据评估模型的温度梯度。此外，对于选定的时间段，显示梯度的实质性变化，我们将整理公布的数据，以评估模型中的一些关键机制，导致模拟的温度梯度，特别是海洋环流，水文循环和植被。我们还将询问模型，以确定模拟梯度变化的原因，包括重点关注海洋环流变化的作用。最后，我们将使用我们以前开发的统计框架来整合我们的模型模拟和地质数据，以探索全球平均温度变化，并将我们的发现传达给其他科学家和公众。总的来说，到项目结束时，我们将在过去5亿年中对过去温度梯度的知识和理解方面取得重大进展，从而更接近我们的最终目标，即全面了解我们星球的气候历史。

The temperature of the Earth today is not uniform everywhere, but, in general, is warmest near the Equator and coldest at the poles (the "meridional temperature gradient"), and varies from west to east, for example with warmer waters in the tropical west Pacific than in the tropical east Pacific (the "zonal temperature gradient"). These gradients are a fundamental property of the climate system - for example being controlled by, and controlling, atmospheric and ocean circulation, water vapour, clouds, and sea ice. The temperature gradients are also crucial for understanding the role of feedbacks (such as the interactions between ice and climate), as well as being important for determining the distribution of many land-surface properties, environments, and ecologies.The primary reasons for these modern temperature gradients are relatively well understood; however, as we go back millions of years into Earth's history, knowledge and understanding of temperature gradients decreases rapidly. Knowledge of past gradients comes primarily from the geological record - estimates of temperature from indirect sources such as fossils. Understanding of the physical mechanisms that controlled past gradients comes primarily from climate models, which can be configured to run for intervals in the past and whose results can be interrogated to determine the reasons for past changes in gradients. However, estimates of past gradients are limited to a few "snapshots" of time that have been studied in detail, and results from many models have been inconsistent with the geological record for those time periods. Because temperature gradients are such a fundamental property of the climate system, without a robust knowledge and understanding of past gradients, we cannot begin to claim to understand the climate history of our planet - which is a first-order blue-skies question.Several recent developments mean that we are now in a position to make substantial progress on this "grand challenge" question. Firstly, there has been a recent push from the geological community to collate, quality-control, and make available an extensive database of past temperatures over the last 500 million years. This database provides an ideal source for reconstructing temperature gradients over time. Secondly, recently we have been developing a version of the UK Met Office climate model that can produce temperature gradients in agreement with the geological record at selected snapshots in time which have been studied, and which can run fast enough on a supercomputer to allow us to carry out the required number of simulations. As such, with these new tools at our disposal, we are ideally placed to study this question.In particular, in this proposed project we will analyse the new database to reconstruct temperature gradients through the Phanerozoic, carry out new climate model simulations through the same time period, and evaluate the temperature gradients from the model with the temperature data. In addition, for selected time periods that show substantial changes in gradients, we will collate published data to evaluate some of the key mechanisms in the model that lead to the modelled temperature gradients, in particular ocean circulation, the hydrological cycle, and vegetation. We will also interrogate the model to ascertain the reasons for the modelled changes in gradients, including a focus on the role of changes in ocean circulation. Finally, we will integrate our model simulations and the geological data using a statistical framework that we have previously developed to explore global average temperature changes, and communicate our findings to other scientists and to the general public.Overall, by the end of the project we will have made a step-change in our knowledge and understanding of past temperature gradients over the last half a billion years, and therefore be closer to our ultimate goal of fully understanding the climate history of our planet.