PaleoGradPhan: Paleoclimate meridional and zonal Gradients in the Phanerozoic

今天地球的温度并不是到处都一样，但总的来说，赤道附近最热，两极最冷（“经向温度梯度”），而且从西到东是不同的，例如热带西太平洋的水温比热带东太平洋的水温高（“纬向温度梯度”）。这些梯度是气候系统的基本属性——例如，受大气和海洋环流、水蒸气、云和海冰的控制和控制。温度梯度对于理解反馈的作用（如冰与气候之间的相互作用）也是至关重要的，对于确定许多陆地表面特性、环境和生态的分布也很重要。这些现代温度梯度的主要原因已相对较好理解；然而，当我们回顾数百万年前的地球历史时，对温度梯度的认识和理解迅速减少。对过去温度梯度的了解主要来自地质记录，即间接来源（如化石）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式，这些模式可以配置为在过去的间隔时间内运行，其结果可以被询问，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已经被详细研究过的几个时间“快照”，而且许多模型的结果与那些时期的地质记录不一致。因为温度梯度是气候系统的基本属性，如果没有对过去的梯度的强大知识和理解，我们就不能开始声称了解我们星球的气候历史——这是一个一级蓝天问题。最近的一些事态发展意味着，我们现在能够在这一“重大挑战”问题上取得实质性进展。首先，最近有一项来自地质学界的推动，要求对过去5亿年间的温度进行整理、质量控制，并提供一个广泛的数据库。该数据库为重建温度梯度随时间的变化提供了理想的来源。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，它可以在选定的快照中产生与地质记录一致的温度梯度，并且可以在超级计算机上运行得足够快，使我们能够进行所需数量的模拟。因此，有了这些新工具，我们就能很好地研究这个问题。特别是，在本项目中，我们将分析新数据库，重建显生宙的温度梯度，进行同一时期的新气候模式模拟，并利用温度数据评估模型的温度梯度。此外，对于显示出显著梯度变化的选定时间段，我们将整理已发表的数据，以评估模型中导致模拟温度梯度的一些关键机制，特别是海洋环流、水文循环和植被。我们还将对模型进行询问，以确定模拟的梯度变化的原因，包括关注海洋环流变化的作用。最后，我们将使用我们之前开发的用于探索全球平均温度变化的统计框架整合我们的模型模拟和地质数据，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，我们对过去5亿年温度梯度的认识和理解将会有一个阶段性的改变，因此，我们更接近于完全了解地球气候历史的最终目标。

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.