Fragmentation and melt of Arctic sea ice

北极海冰是气候变化的重要因素和指标；过去几十年来，海冰的迅速减少给科学家、决策者和公众敲响了警钟。海冰的退缩导致了跨北极航运的增长，以及从海底开采矿物和化石燃料的计划。政府间气候变化专门委员会（IPCC）的最新评估得出结论，假设温室气体排放继续增加，到2050年，北极很可能会成为可靠的无冰地区。然而，IPCC所使用的气候模拟常常不能真实地捕捉北极海冰的大尺度特性，如范围、变率和近期趋势。因此，有必要改进对北极海冰的模拟，以便更好地了解最近观测到的变化和对未来的可靠预测，以帮助评估风险和机遇，并为有关适应和缓解的重要决策提供信息。近年来对北极的观测有所改善：新的卫星正在从空间测量海冰厚度和地形，最近和计划中的大量实地方案有助于我们了解控制冰盖演变的现场过程。这些观测不仅揭示了北极冰盖的范围和厚度在所有季节都在减少，而且还向我们展示了冰是如何减少的。特别是，最近的观察表明，地表融化池是如何削弱冰的，将其破碎成许多浮冰。海冰演变的任何可操作的环境或气候模式都没有考虑到冰破碎的过程或具有一系列不同海冰大小的影响。海冰的大小影响横向融化、空气到海洋的动量转移、流变学和波冰相互作用。理想模型研究表明，考虑浮冰破碎对海冰的空间分布具有领先的影响，并降低了海冰的总体范围和体积。由于现有的气候模型不包含这种物理特性，它们在理解和预测北极的可变性和变化方面的效用受到了损害。由于经向大气和海洋环流的误差以及北极的冰输出，这也导致低纬度地区气候模式精度的损害。这一建议将确定海冰破碎在北极海冰加速消退中的作用。结合新的和新兴的观测，新的理论和过程模型，我们将建立对海冰破碎的基本理解。我们将a)开发一个高保真度、高分辨率的海冰热力学和力学演化模型，并利用该模型和观测数据来探索海冰破碎；b)建立破碎过程的参数化，包括第一个融化破碎模型，并将其纳入气候和天气模型的海冰成分；c)使用冰-海洋和完全耦合的气候模型来确定破碎对以下方面的贡献：过去几十年的快速冰损失，对未来几十年冰损失的预测，以及现在为业务冰预报创造技能。除了科学成果之外，拟议的工作还将产生一个新的海冰破碎模块，交付给气候和天气建模小组：英国国内的气象局、国家海洋学中心、英国南极调查局和欧洲中期天气预报中心。

Arctic sea ice is an important agent, and indicator, of climate change; the rapid decline of sea ice in past decades has been a wake-up call to scientists, policy-makers, and the general public. This retreat of the sea ice has led to growth of trans-Arctic shipping and plans to extract minerals and fossil fuels from the ocean floor. The latest assessment of the Intergovernmental Panel on Climate Change (IPCC) concluded that it was likely that the Arctic would become reliably ice-free by 2050 assuming greenhouse gas emissions continue to increase. However, the climate simulations used by the IPCC often fail to realistically capture large scale properties of the Arctic sea ice, such as the extent, variability and recent trends. Therefore, there is a need to improve simulations of Arctic sea ice to provide better understanding of the recent observed changes and credible projections of the future to help assess risks and opportunities and inform important policy decisions about adaptation and mitigation.Observations of the Arctic have improved in recent years: new satellites are measuring sea ice thickness and topography from space, and substantial recent and planned field programmes are contributing to our knowledge of the in situ processes controlling the evolution of the ice cover. These observations reveal not only that the extent and thickness of the Arctic ice cover is reducing in all seasons, but also show us how the ice is decreasing. In particular, recent observations demonstrate how surface melt ponds weaken the ice, fragmenting it into many floes. No operational environmental or climate model of sea ice evolution takes into account the processes of ice fragmentation or the impact of having a range of different sea ice floe sizes. Sea ice floe size affects lateral melting, air to ocean momentum transfer, rheology, and wave-ice interaction. Idealised model studies demonstrate that accounting for floe fragmentation has a leading order impact on the spatial distribution of sea ice and decreases its overall extent and volume. Because existing climate models do not contain this physics, their utility for understanding and predicting variability and change in the Arctic is compromised. This leads to impairment of climate model accuracy at lower latitudes also, due to errors in meridional atmospheric and oceanic circulations, as well as ice export from the Arctic. This proposal will determine the role of sea ice fragmentation in the accelerated retreat of Arctic sea ice. Using a combination of new and emerging observations, new theory and process modelling, we will build fundamental understanding of sea ice fragmentation. We will a) develop a high fidelity, high resolution model of sea ice thermodynamic and mechanical evolution and use this, and observations, to explore sea ice fragmentation, b) build parameterisations of fragmentation processes, including the first model of fragmentation by melt, and incorporate these into the sea ice component of climate and weather models, and c) use ice-ocean and fully coupled climate models to identify the contribution of fragmentation to: rapid ice loss over past decades, projections of ice loss in the coming decades, and creating skill for operational ice forecasts now.In addition to the scientific outcomes, the proposed work will result in a new sea ice fragmentation module delivered to climate and weather modelling groups: within the UK, the Met Office, the National Oceanography Centre, the British Antarctic Survey, and the European Centre for Medium-Range Weather Forecasts.