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驱动因素如何影响北大西洋的海洋环流。这种环流将大部分热量输送到北大西洋，也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时不可逆转地停止，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上一次评估报告称，21世纪大西洋环流只会出现温和下降。NERC正在资助两个海洋观测阵列。这些系统应能提供有关大西洋环流变化的高质量信息，但大约从2005年起才开始运行。因此，仅凭它们无法推断2005年前大西洋环流的变化。这些阵列的操作和维护费用很高，将于2011年对其重要性进行评估。对海洋环流的直接观测很少，但通过使用海洋模型并结合这些观测，有可能对大规模海洋环流作出估计。不同的研究小组使用不同的方法，通过这些海洋再分析得出了对环流变化的不同估计。我们将使用现有的一组估计，并将它们与关键观察结果进行比较，并在后续分析中使用针对这些观察结果进行验证的结果。使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型模拟的变化的“指纹”。这一分析将允许估计大西洋中人类和自然驱动的总变化，并根据我们对发生的事情的最佳估计对模型模拟变化进行测试。如果模型很好地符合已经发生的情况，那么我们就增加了对它们未来预测的信心；如果不符合，那么我们就有证据表明模型存在重大错误，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。我们计划首先考虑的是一种自然的多年代际变化模式，称为大西洋多年代际振荡。我们将探索这种模式能在多大程度上解释大西洋与人类驱动的变化的差异，以及提出的这种模式存在的机制是否得到观测证据的支持。另一个可能影响海洋循环的因素是大气风；它通过对海洋的直接影响以及通过进出海洋的热量和淡水的变化来实现。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的模拟，迫使大气环流接近观测到的环流，以检验这一假设。最后，我们将通过提出这样一个问题来为快速资助的海洋观测阵列的评估做出贡献：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？我们将使用模型模拟和经过验证的海洋再分析的结果，并模拟阵列将看到的情况，从而实现这一点。这将使人们能够估计海洋观测阵列将能够检测到什么样的变化。

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.