Quantifying Human Influence on Ocean Melting of the West Antarctic Ice Sheet

南极西部冰原（WAIS）是一块巨大的冰川冰板，大约有欧洲那么大，有几公里厚。卫星观测显示，西洋带正在失去冰，这导致全球海平面上升。如果目前的冰流失速度继续下去，到2100年，仅WAIS就将导致全球海平面上升50厘米。冰的损失是由于漂浮在冰架之下的海洋融化加剧造成的。在南极洲的阿蒙森海地区，海洋融化导致冰架迅速变薄。这些融化变化的最终原因尚不清楚。地球的气候经历了巨大的自然变化，我们知道这些变化对阿蒙森海有很大的影响。因此，我们不知道WAIS融化的增加是由人类引起的气候变化引起的，还是由自然变化引起的。这个项目将解决这个问题。英国和日本的科学家在开发阿蒙森海的冰和海洋的计算机模型方面处于世界领先地位。我们将在过去和未来广泛的大气条件下强迫这些模式，包括自然变率和人为引起的变化。这些强迫将取自全球气候模式模拟。通过综合考虑所有这些模型的结果，并对许多可能的自然变率的例子进行平均，我们将能够确定人类引起的变化的重要性。为了对这些结果有信心，我们需要知道是什么海洋过程导致了我们发现的模型行为。我们将通过逐步禁用模型中的每个过程并调查结果来量化不同过程的重要性。我们还必须确保这些模式能很好地反映该地区的海洋状况。然而，这是很困难的，因为阿蒙森海很遥远，观测很少。为了提供关键的模型验证，我们将创建该地区过去25年的洋流新记录，使用最新的卫星处理技术来确定甚至在厚海冰覆盖的地区的洋流。这些结果将使我们能够确定目前的冰损失是否是由过去的人类活动造成的，以及未来的融化是否可以通过减少温室气体的排放来减少。这将使政治家和公众能够决定如何最好地应对来自西海的海平面上升。

The West Antarctic Ice Sheet (WAIS) is a huge slab of glacier ice about the size of Europe, and a few kilometres thick. Satellite observations show that the WAIS is losing ice, and this is causing global sea level to rise. If the current rate of ice loss continues, the WAIS alone will cause 50 cm of global sea-level rise by 2100. The ice loss is caused by increased ocean melting beneath areas of floating glacial ice called ice shelves. In the Amundsen Sea region of Antarctica, ocean melting is causing the ice shelves to thin very rapidly. The ultimate cause of these changes in melting is not known. Earth's climate experiences large natural variations, and we know that these variations have a strong influence on the Amundsen Sea. As a result, we don't know whether the increased melting of the WAIS is caused by human-induced climate change, or by natural variability. This project will address that question.Scientists in the UK and Japan are leading the world in developing computer models of the ice and ocean in the Amundsen Sea. We will force these models with a wide range of atmospheric conditions for the past and future, including both natural variability and human-induced changes. These forcings will be taken from global climate model simulations. By considering the results of all these models together, and averaging over many possible examples of the natural variability, we will be able to determine the importance of human-induced changes.In order to be confident in these results, we need to know what ocean processes are causing the model behaviour that we find. We will quantify the importance of different processes by progressively disabling each process in the model and investigating the result. We must also be sure that the models are a good representation of ocean conditions in the region. However, this is difficult because the Amundsen Sea is remote and very poorly observed. To provide the crucial model validation, we will create a new record of ocean currents in the region over the last 25 years, using the latest satellite processing techniques to determine ocean currents even in regions covered by thick sea ice.These results will allow us to determine whether the present ice loss was caused by human activities in the past, and whether melting in the future can be reduced by lower emissions of greenhouse gases. This will enable politicians and the public to decide how best to respond to sea-level rise from the WAIS.