Understanding rising seas and ice by linking coupled models and past climates

由于温室气体的排放，海平面变化是气候变化最广为人知的潜在严重后果之一。它涉及公众和决策者，因为它对沿海和低洼地区的人口和生态系统产生不利影响。这种影响预计将在未来几个世纪内增加。尽管英国可能在几十年或更长时间内都不会感受到海平面重大变化的影响，但现在能够对海平面变化做出可靠的预测，具有巨大的社会经济效益。例如，需要对沿海基础设施做出规划决定，比如泰晤士河屏障，它耗资数十亿英镑，必须持续数十年。极地冰盖融化对海平面变化的贡献自1993年以来已经使全球海平面上升了约20毫米，预计这一速度将在21世纪继续增长。这也是海平面变化预算中最不确定的部分，这在很大程度上是因为，气候和冰盖模型的配合效果严重限制了模拟大冰盖如何随气候演变的科学。我们需要了解导致极地冰盖质量损失的物理过程之间的相互作用，并不仅预测最有可能的海平面变化量，而且还需要为更极端的情况分配概率(这种可能性可能较小，但影响要大得多)正变得越来越迫切。例如，目前的ISMIP6项目是世界气候研究方案的一项国际多冰盖模式活动，是在政府间气候变化专门委员会范围内预测冰盖对未来海平面变化的贡献的第一项国际合作努力。然而，目前缺乏关于气候和冰盖共同演化的科学知识，这要求冰盖建模人员在进行这样的预测时采用一些捷径。这些模型需要这些捷径来描述气候变化对冰盖的影响(反之亦然)，它们限制了我们对未来的预测。国际社会正在开发新的气候和冰盖模型，它们一起运行，并直接相互作用。这些可以帮助我们理解气候和冰盖如何相互反馈的物理原理，但很难确保这些模型是准确的，因为我们没有太多关于反馈实际上是如何运行的观察--上一次地球上冰盖和气候的重大变化一起发生是在数千年前。在这个项目中，我们将把过去那些重大变化的证据与对冰盖的现代观测结合起来，并使用它们来评估我们耦合的气候和冰盖模型的工作情况，并使模型更接近实际。这将有助于我们更多地了解气候和冰盖反馈过程，并使用新的统计方法，使我们能够在考虑到这些反馈的情况下对冰盖如何变化做出新的预测，并可以展望更远的未来。我们改进的模型还将告诉我们，当我们不得不单独运行冰盖模型时，如何才能做出更好的未来海平面预测。我们的最终目标是提高我们对气候-冰盖相互作用的理解，并为冰盖和气候模型社区配备更好的工具，以预测未来的海平面变化。

Sea level change is one of the mostly widely recognised and potentially serious consequences of climate change due to emissions of greenhouse gases. It concerns both public and policymakers, because of its adverse impact on the populations and ecosystems of coastal and low-lying areas. This impact is expected to increase for centuries to come. Although the impact of major sea level changes may not be felt in the UK for decades or longer, being able to make reliable projections of sea level change now is of large socio-economic benefit. For example, planning decisions need to be made concerning coastal infrastructure, such as the Thames Barrier, that costs billions of pounds and must last for decades.The contribution to sea level change from melting polar ice sheets has already raised global sea levels by around 20mm since 1993, and this rate is expected to grow over the 21st century. It is also the most uncertain part of the sea level change budget, largely because the science of modelling how large ice sheets evolve together with climate has been severely limited by how well climate and ice sheet models work together. Our need to understand the interplay between the physical processes that are resulting in the loss of mass from polar ice sheets and make projections of not only the most likely amount of sea level change, but also to assign probabilities to more extreme cases (which may be less likely, but have much greater impact) is becoming increasingly urgent. For instance, the current ISMIP6 project, an international multi-ice sheet model activity of the World Climate Research Programme, is the first international, collaborative effort to make projections of the ice sheet contribution to future sea-level change within the context of the Intergovernmental Panel on Climate Change. However, the present lack of scientific knowledge about the co-evolution of climate and ice sheets requires ice sheet modellers to adopt a number of short-cuts in carrying out projections like this. These short-cuts are needed in the models to describe how the ice sheets may be affected by the changing climate (and vice-versa) and they limit how far ahead into the future we can make projections.The international community are developing new climate and ice sheet models that run together and interact directly with each other. These can help us understand the physics of how climate and ice sheets feed back on each other, but it can be difficult to be sure that these models are accurate, as we do not have many observations of how the feedbacks really operate in practice - the last time major changes in ice sheet and climate happened together on Earth was thousands of years ago. In this project we will combine evidence from those major past changes with modern observations of ice sheets, and use them to assess how well our coupled climate and ice sheet models work and to make the models more physically realistic. This will help us understand more about climate and ice sheet feedback processes, and, using novel statistical methods, will let us make new projections of how ice sheets will change that take account of these feedbacks and can look further into the future. Our improved models will also tell us about how we can make better future sea-level projections when we have to run ice sheet models alone. We ultimately aim to improve our understanding of climate-ice sheet interactions and equip the ice sheet and climate modelling communities with better tools to make future projections of sea level change.