What are the roles of natural and human drivers in historical changes in the Atlantic Meridional Circulation?

我们研究的主要目的是了解人类和自然因素是如何影响北大西洋的海洋环流的。这种环流将大部分热量输送到北大西洋，是欧洲和英国相对温暖的部分原因。一些模型表明，它可能会在气候变化中不可逆转地停止，这可能会使欧洲降温1-3摄氏度。根据对几种不同气候模型的分析，政府间气候变化专门委员会的最后一次评估报告称，大西洋环流在21世纪只会出现温和的下降。NERC正在资助两个海洋观测阵列。这些应该能提供关于大西洋环流变化的高质量信息，但大约从2005年才开始运行。因此，仅凭它们自己无法推断2005年以前大西洋环流的变化。这些阵列的操作和维护成本很高，对其重要性的评估将在2011年进行。对海洋环流的直接观测很少，但通过将海洋模式与这些观测相结合，有可能对大尺度海洋环流进行估计。不同的研究小组使用不同的方法，从这些海洋再分析中得出了对环流变化的不同估计。我们将使用现有的估计集，并将它们与关键观察结果进行比较，并在后续分析中使用验证这些观察结果的估计集。利用经过验证的海洋再分析和现有的海洋温度分析，我们将比较来自大量气候模式模拟的变化的“指纹”。这一分析将使我们能够估计大西洋中人类和自然驱动的总变化，并根据我们对已经发生的事情的最佳估计来测试模型模拟的变化。如果这些模型与已经发生的情况吻合得很好，那么我们就增加了对它们对未来预测的信心；如果不是，那么我们有证据表明存在严重的模型错误，因此需要改进模型。我们还将分别研究人类和自然驱动因素对大西洋的影响，以估计它们对变化的贡献。其他因素也会影响北大西洋的气候和环流。我们计划考虑的第一个是自然的多年代际变率模式，称为大西洋多年代际振荡。我们将探讨这种模式在多大程度上可以解释大西洋与人类驱动的变化之间的差异，以及所提出的存在机制是否得到观测证据的支持。另一个影响海洋环流的因素是大气风；既通过对海洋的直接影响，也通过进出海洋的热量和淡水量的变化。海洋温度和淡水含量的变化会影响海洋密度，从而影响海洋环流。一些科学家提出，大气环流的变化是海洋温度和环流变化的原因。我们计划进行一些新颖的模拟，其中大气环流被迫接近观察到的，以验证这一假设。最后，我们将对RAPID资助的海洋观测阵列的评估做出贡献，提出这样一个问题：“这些阵列本身能告诉我们多少关于大西洋环流变化的信息？”我们将通过使用模型模拟的结果和经过验证的海洋再分析，并模拟阵列将看到的情况来做到这一点。这将使我们能够估计海洋观测阵列能够探测到什么样的变化。

The main aim of our research is to see how human and natural drivers have affected the ocean circulation in the North Atlantic. This circulation transports much of the heat into the North Atlantic and is partly responsible for the relative warmth of Europe and the UK. Some models suggest it might irreversibly stop in a changed climate which could cool Europe by 1-3 degrees centigrade. Based on the analysis of several different climate models the last Intergovernmental Panel on Climate Change assessment reported that the Atlantic circulation would show only a modest decline in the 21st century. NERC is funding two ocean observing arrays. These should produce high quality information on changes in the Atlantic Circulation but have only been operating since about 2005. Consequently, on their own, they cannot infer changes in the Atlantic circulation prior to 2005. These arrays are expensive to operate and maintain and an evaluation of their importance is to be made in 2011. Direct observations of the ocean circulation are sparse but through using ocean models in combination with these observations it is possible to make estimates of the large scale ocean circulation. Different research groups using different approaches have produced different estimates of changes in the circulation from these ocean reanalyses. We will use the existing set of estimates and compare them with key observations and use those that validate against those observations in our subsequent analyses. Using the validated ocean reanalyses and existing analysis of ocean temperatures we will compare 'fingerprints' of change from a large number of climate model simulations. This analysis will allow an estimate of the total human and naturally driven changes in the Atlantic and testing of model simulated changes against our best estimate of what has happened. If the models agree well with what has happened then we have increased confidence in their future predictions; if not then we have evidence of significant model error and thus a need to improve models. We will also separately examine the effect of human and natural drivers on the Atlantic to estimate their contribution to change. Other factors can also affect the climate and circulation of the North Atlantic. The first we plan to consider is a natural multi-decadal mode of variability called the Atlantic Multi-decadal Oscillation. We will explore how much of the difference from human driven changes in the Atlantic can be explained by this mode and if the proposed mechanisms for its existence are supported by observational evidence. Another factor that can affect the ocean circulations is the atmospheric winds; both through a direct effect on the ocean and through changes in the amount of heat and fresh-water moved in and out of the ocean. Changes in the temperature and fresh-water content of the ocean affect ocean density and thus the ocean circulation. Some scientists have suggested that changes in atmospheric circulation are responsible for changes in ocean temperature and circulation. We plan to carry out some novel simulations in which the atmospheric circulation is forced to be close to that observed in order to test this hypothesis. Finally we shall contribute to the evaluation of the RAPID funded ocean observing arrays by asking the question: 'How much would the arrays have told us, on their own, about changes in the Atlantic Circulation?' We will do this by using results from model simulations and the validated ocean reanalysis and simulating what the arrays would have seen. This will allow an estimate of what kind of changes the ocean observing arrays would be able to detect.