Advaenced state estimats of the ocean and cryosphere: innovative new tools to better understand, predict, and prepare for sea level changes

海平面上升（SLR）是当今人类面临的最严重的适应挑战之一。SLR增加了风暴潮、沿海洪水和侵蚀的频率和严重程度，从而破坏了关键的基础设施，阻碍了经济活动，并可能使全球1亿多沿海社区居民流离失所。在“一切照旧”的情况下，到2100年，海平面上升86厘米的情况下，全球每年的洪水损失可能会增加到10万亿英镑以上。尽管它很重要，但本世纪单反的发展前景非常不确定。SLR预测中最大的不确定性来自南极西部冰盖（WAIS），如果它完全融化，最终有可能使海平面上升3米以上。南极海岸线上突出的大型漂浮冰架像水坝一样，阻止了WAIS流入海洋，也阻止了海平面的上升。这些重要的冰架正在迅速融化；近几十年来，所有南极冰架的冰损失率增加了12倍以上。冰架是非常动态的系统，可以对海洋环流的变化做出快速反应，例如，在冰架下面增加的温水入侵可以使它们从下面融化。近期和中期未来海平面迅速上升的威胁突出表明，有必要进一步了解洋流如何将热量输送到南极冰架脆弱的底部。到目前为止，这一领域的进展一直受到从有限的观测数据中提取详细的热收支、冰架融化速率和灵敏度的挑战。在这项研究中，我将使用敏感性分析技术（即伴随建模）来建立下一代海洋和冰架建模框架，这将使我们做出稳健和有用的单反预测的能力发生重大变化。我将第一次将观测结果和现实物理模型结合在一个分层海洋-冰状态估计框架中，这将使我能够：(1)获得在海洋-冰界面上对融化速率和其他难以观测的参数的空间变化、观测受限的估计；(2)量化海冰界面的热含量和融化速率对局地和远地海气相互作用和海洋环流的敏感性；(3)建立空间和时间上详细的热量收支，以跟踪热量如何从公海传递到冰架；(4)通过智能定位关键位置进行新的测量，优化未来的观测活动。这种海冰状态估计框架将适用于地球上的任何海冰系统，有可能改变我们理解这些关键海平面调节器现在和未来行为的能力。因此，全球社会将获得更好的信息，从而能够更好地应对海平面上升，减少对低洼基础设施、社区和企业的风险。

Sea level rise (SLR) is one of the most serious adaptation challenges facing humanity today. SLR increases the frequency and severity of storm surges, coastal flooding, and erosion, thereby damaging critical infrastructure, hampering economic activity, and potentially displacing more than 100 million people globally who live in coastal communities. Under "business as usual" conditions, global flood costs could increase to over £10tn per year by 2100, under 86 cm of sea level rise. Despite its importance, projections of SLR over this century are very uncertain. The greatest single source of uncertainty in SLR projections comes from the West Antarctic Ice Sheet (WAIS), which has the potential to eventually raise sea levels by over three metres if it melts entirely. The WAIS is held back from flowing into the ocean and raising sea levels by large floating ice shelves that protrude from the Antarctic coastline, acting like dams. These crucial ice shelves are melting increasingly rapidly; in recent decades, the rate of ice loss from all Antarctic ice shelves has increased by more than a factor of twelve. The ice shelves are very dynamic systems that can respond quickly to changes in ocean circulation, e.g. increased intrusion of warm water under the ice shelves can melt them from underneath. The threat of rapidly rising seas in the near-to-medium term future highlights the need for improved understanding of how ocean currents deliver heat to the vulnerable undersides of Antarctic ice shelves. Thus far, progress in this area has been hampered by the challenges associated with extracting detailed heat budgets, ice shelf melt rates, and sensitivities from a limited set of observations. In this Fellowship, I will use sensitivity analysis techniques (i.e. adjoint modelling) to establish a next-generation framework for ocean and ice shelf modelling that will make a step change in our ability to make robust and useful SLR projections. I will, for the first time, combine observations and realistic physical models in a hierarchical ocean-ice state estimation framework that will allow me to: (1) obtain spatially-varying, observationally-constrained estimates of melt rates and other hard-to-observe parameters at the ocean-ice interface; (2) quantify the sensitivities of heat content and melt rates at the ocean-ice interface to local and remote air-sea interactions and ocean circulation; (3) create spatially and temporally detailed heat budgets to track how heat is delivered from the open ocean to the ice shelves; and (4) optimise future observing campaigns by intelligently targeting key locations for new measurements. This ocean-ice state estimation framework will be applicable to any ocean-ice system on Earth, offering the potential to transform our ability to understand the present and future behavior of these key sea level regulators. As a result, global societies will be better informed and hence better able to respond to sea level rise, reducing risks to low-lying infrastructure, communities, and businesses.