Modelling ice-sheets, climate and sea-level during the last glacial cycle

冰盖的反复形成、前进、后退和消失是过去一百万年冰川循环的决定性特征。在21,000年前的末次冰盛期，北半球广阔的冰盖对全球和区域气候产生了重大影响，全球平均海平面比现在低了120米，这主要是因为陆地上储存的冰中的水要多得多。冰盖和气候相互作用强烈。冰盖通过其对降雪和融化的影响对气候变化非常敏感。它们通过几种机制反馈区域和全球气候变化；例如，阳光被冰雪反射，地表温度因海拔上升而降温，融化的冰盖流入海洋可能会影响海洋循环。在冰川旋回期间发生的气候和冰盖的巨大而复杂的变化在几个重要方面或细节上没有得到了解。解释它们是地球系统科学的一项激动人心的智力挑战。人为气候变化对格陵兰和南极洲冰盖的影响可能会在未来几个世纪内使全球平均海平面发生多米的变化，对沿海人口和生态系统造成严重影响。从长远来看，如果气候变化逆转，冰盖可能会重新生长。仅凭当时的观察，我们对相关过程的了解不足以做出可靠的预测，因为上个世纪相对较好的观察期间的变化相对较小。因此，记录冰川周期中发生的更大的自然变化，是了解冰盖未来可能如何应对和影响气候变化的重要信息来源。该项目的目的是调查气候和北半球冰盖在上一次冰川周期中的共同演变。我们将第一次使用用于详细的未来气候预测的气候模型类型，以及详细的冰盖模型来实现这一点。重点是分析这些计算机模型模拟的变化，并将其与观测数据进行比较。预期的成果将是：(1)用比以前使用的更加完整的模型模拟上一次冰川周期，包括对模型系统不确定性对结果的影响进行量化；(2)在数百年至数千年的时间尺度上改进对冰盖变化及其与气候的相互作用的科学认识；(3)提高对人为气候变化造成的冰盖变化进行模拟的能力。这显然具有现实的社会经济意义，因为我们希望能够对未来做出预测。

The repeated formation, advance, retreat and disappearance of ice-sheets is the defining characteristic of the glacial cycles of the last million years. At the Last Glacial Maximum (LGM), 21,000 years ago, the extensive Northern Hemisphere ice-sheets had a major influence on global and regional climate, and global-mean sea-level was 120 m lower than present, mainly due to the much greater mass of water stored in ice on land. Ice-sheets and climate interact strongly. Ice-sheets are very sensitive to climate change through its effect on snowfall and melting. They feed back on regional and global climate change through several mechanisms; for instance, sunlight is reflected by the snow and ice, surface temperature is cooled by raised elevation, and meltwater running off the ice-sheet into the sea may influence ocean circulation. The enormous and complex changes in climate and ice-sheets which take place during glacial cycles are not understood in several important respects or in detail. Explaining them is an exciting intellectual challenge of Earth system science. The effect of anthropogenic climate change on the ice-sheets of Greenland and Antarctica could produce changes in global-mean sea-level of many metres over future centuries, with severe impacts on coastal populations and ecosystems. On the longer term, if climate change were reversed, the ice-sheets might regrow. Contemporary observations alone give us insufficient knowledge of the relevant processes to make reliable predictions, because changes during the relatively well-observed last century have been relatively small. Therefore the record of the larger natural variations that occur during glacial cycles is a crucial source of information about how ice-sheets may respond to and influence climate change in the future. The aim of this project is to investigate the co-evolution of the climate and the Northern Hemisphere ice-sheets during the last glacial cycle. For the first time we will do this using the type of climate model used for detailed future climate projections, coupled to a detailed ice-sheet model. The focus is on analysis of changes simulated by these computer models, which we compare with observational data. The intended outcomes will be (i) simulations of the last glacial cycle with a much more physically complete model than has been used before, including a quantification of the effect of model systematic uncertainty on the results; (ii) a consequent improvement in scientific understanding of ice-sheet change and its interaction with climate on timescales of centuries to millennia; (iii) an improved capability for modelling ice-sheet changes that will result from anthropogenic climate change. This has obvious practical socio-economic relevance, since we want to be able to make predictions for the future.