Causes of change in European mean and extreme climate over the past 500 years

我们项目的目的是了解过去500年来平均和极端温度以及平均降水量变化的原因，主要集中在欧洲。气候变化和极端气候变化的空间模式很重要，因为气候在区域范围内影响社会和自然世界。通过了解温度和极端温度以及降水在过去发生变化的原因，我们将能够更好地预测未来可能发生的变化。这将是因为我们将提高我们对哪些机制在过去的变化中起重要作用的知识，并测试气候模型再现过去发生的事情的能力。研究人员重建了欧洲过去500年的温度变化，现在可以找到可以追溯到18世纪的长时间同质化仪器记录，在某些情况下，还具有每日分辨率。此外，一些降水和环流的重建正在变得可行，这些数据可以可靠地追溯到大约250年前，但更有局限性，可以追溯到500年前。其他研究人员利用冰盖中记录的数据重建了太阳活动的变化、主要火山喷发的时间和规模以及大气的组成。气候最重要的自然“强迫”一直被认为是太阳辐射的变化。这是根据太阳黑子等太阳活动的测量重建的。然而，另一个可能更重要的气候强迫是大规模火山爆发的影响。它们将硫酸盐气溶胶注入高层大气，反射更多的阳光，导致降温。自18世纪和19世纪以来，人类的力量变得重要起来。人类排放的二氧化碳和其他温室气体很好地混合在一起，因此导致全球变暖的原因大致相同。从18世纪开始，就发生了大规模的森林砍伐。森林的消失使陆地将更多的阳光反射回太空，导致降温。19世纪燃烧的主要化石燃料是煤，煤的燃烧会将硫磺排放到大气中。硫磺形成一种短暂的气溶胶，作用于其排放地附近的降温区域。因此，人类的强迫作用预计将产生相当复杂的地区性影响，在北半球，温室气体造成的变暖部分地被森林砍伐和气溶胶造成的降温所抵消。为了找出在欧洲和北半球观察到的气候变化模式的原因，我们将使用气候模型来模拟由于上述每个人的“强迫”而会发生的情况。然后，我们将使用数学技术将这些“指纹”与过去气候变化和气候变异性的重建进行比较，并确定哪些变化是由外部影响造成的，哪些只是自然变化气候的代表。我们将主要关注欧洲自1500年以来的温度和降水变化模式，但也将探索整个千年变化的原因。比较的结果告诉我们，每种强迫对过去气候变化的相对贡献，以及有多少变化没有得到解释，可能是由于气候的混乱变化而自发发生的。由于气候模型和现实世界一样，具有混乱的可变性，我们将使用几个模拟来分离可预测的分量。利用模型和重建，我们还将探索导致历史变化的机制。

The aim of our project is to understand the causes of variability and change in mean and extreme temperature, and changes in mean precipitation over the last 500 years, largely focusing on Europe. Spatial patterns of climate change and changes in extremes are important since climate affects society and the natural world on regional scales. By understanding why temperature and temperature extremes as well as precipitation have varied in the past, we will be better able to predict how it might vary in the future. This will be because we will have improved our knowledge of what mechanisms were important in changes in the past, and tested the ability of climate models to reproduce what has happened in the past. Researchers have reconstructed European temperature variability over the last 500 years, and long homogenized instrumental records are now available that go back into the 18th century, and in some cases have daily resolution. Also, some reconstructions of precipitation and circulation are becoming available that go back reliably about 250 years, and with more limitations, 500 years. Other investigators have reconstructed changes in solar activity, the timing and magnitude of major volcanic eruptions and the composition of the atmosphere using data recorded in the ice sheets. The most important natural 'forcing' of climate has been thought to be changes in radiation from the Sun. This is reconstructed from measures of solar activity such as sunspots. However, another possibly more important climate forcing is the effect of large explosive volcanic eruptions. These inject sulphate aerosol into the upper atmosphere, which reflect more sunlight, causing cooling. Since the 18th and 19th centuries human forcings have become important. Human emissions of carbon dioxide and other greenhouse gases are well mixed, so cause roughly equal warming everywhere. From the 18th century on substantial deforestation took place. The removal of forest makes the land reflect more sunlight back to space, causing a cooling. The main fossil fuel burnt in the 19th century was coal, whose burning causes sulphur to be emitted to the atmosphere. The sulphur forms a short-lived aerosol which acts to cool regions close to where it is emitted. Thus, human forcings would be expected to have a rather complex regional affect with, in the Northern Hemisphere, warming from greenhouse gases being, partly to fully, offset by cooling due to deforestation and aerosols. To find causes of the observed patterns of climate change over Europe and the Northern hemisphere we will use climate models that can simulate what would have happened due to each individual 'forcing' described above. Then using mathematical techniques we will compare these 'fingerprints' with reconstructions of past climate change and climate variability and determine which changes have been caused by external influences, and which are just a representation of a naturally varying climate. We will mainly focus on patterns of temperature and precipitation change over Europe since 1500, but also explore the causes of changes over the entire millennium. The results of the comparison tell us the relative contribution of each forcing to past climate change, and how much change is left unexplained and may have occurred spontaneously due to chaotic variability in the climate. Since climate models, like the real world, have chaotic variability, we will use several simulations to isolate the predictable component. Using models and reconstructions, we will also explore the mechanisms responsible for the historical changes.