Towards a marginal Arctic sea ice cover

最近观测到的北极变化已成为全球气候变化的“典型代表”，特别是因为夏季海冰面积在过去35年中迅速缩小。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，随着新的卫星从太空测量海冰特性，对北极的观测有所改善。这些卫星不仅揭示了北极冰盖的范围和厚度在所有季节都在减少，而且边缘冰区（MIZ）——一个由相对分散的小浮冰组成的低冰面积集中区域——也在增长。模式预测显示，到2050年，MIZ将从夏季海冰覆盖的10%左右增长到80%，使迄今为止相对平静的北冰洋暴露在大气中。空气、冰和海洋之间的非线性相互作用，放大或缩小变化，被称为反馈，与减少和边缘海冰覆盖有关，将在未来几年出现或占据主导地位。在当前的模型中，许多反馈要么完全不存在，要么没有得到充分的捕捉。例如，不包括反馈，即由于冰融化或在海浪压力下破裂而产生的更小的浮冰促进了进一步的横向融化和波浪向更深处的传播，进一步扩大了MIZ。由于现有的气候模式过度简化了这些反馈，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以及北极冰输出的误差，这也导致低纬度地区气候模式精度的损害。我们将利用现有和新的观测资料研究控制MIZ演变的过程。我们将包括波冰相互作用的物理，冰的破裂和融化，和浮冰碰撞成冰，海洋，和气候模型。我们将使用这些模型，通过新的观测加以约束和验证，通过一系列数值实验来探索海冰、海洋和大气之间的反馈。我们将量化MIZ增加对北极物理气候的影响，并探索导致北极海冰预计损失的过程。

Recent observed changes in the Arctic have become a 'poster child' for global climatic changes, particularly because the summer sea ice extent has shrunk rapidly over the past 35 years. 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 with new satellites measuring sea ice properties from space. These satellites reveal not only that the extent and thickness of the Arctic ice cover is reducing in all seasons but that the Marginal Ice Zone (MIZ), a region of low ice area concentration consisting of a relatively disperse collection of small floes, has grown.Model projections indicate the MIZ will grow from around 10% to 80% of the summer sea ice cover by 2050, exposing a hitherto relatively quiescent Arctic Ocean to the atmosphere. Nonlinear interactions between the air, ice, and ocean that magnify or diminish change, known as feedbacks, associated with a reduced and marginal sea ice cover will emerge or assume dominance in the coming years. Many of these feedbacks are either entirely absent or inadequately captured in current models. For example, not included is the feedback whereby the creation of smaller floes due to ice melt or breakup under ocean wave stress promotes further lateral melt and propagation of waves deeper into the pack, further enlarging the MIZ. Because existing climate models oversimplify these feedbacks, 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. We will investigate processes controlling evolution of the MIZ using existing and new observations. We will include physics of wave-ice interaction, ice breakup and melt, and floe collisions into ice, ocean, and climate models. We will use these models, constrained and verified with new observations, to explore feedbacks between the sea ice, ocean, and atmosphere using a series of numerical experiments. We will quantify the impact of the increase in the MIZ on the Arctic physical climate, and explore the processes responsible for the projected loss of Arctic sea ice.