Collaborative Research: Assessing the Global Climate Response to Melting of the Antarctic Ice Sheet

有令人信服的历史证据表明，西南极冰盖（WAIS）很容易迅速退缩和崩溃。与20-30年前的观测相比，最近的观测表明，冰架（下面是海洋的厚冰）和陆地冰（下面是陆地的厚冰）现在都在以更快的速度融化。一些数值模型表明，在我们有生之年，大规模的冰川退缩可能会开始，从松岛和思韦茨冰川在未来50年的突然崩塌开始。这可能会导致大部分WAIS的退缩，然后是东南极冰盖（EAIS）部分的崩溃。该研究项目将评估如果大量淡水和冰流入南大洋，全球海洋环流和气候将受到何种程度的影响。它将确定在不久的将来，WAIS的快速崩溃是否会对现代气候和人类社会的稳定构成任何重大威胁。这是一个迄今为止很少受到关注的话题，因为大多数先前的研究都集中在气候对格陵兰冰盖融化的反应上。然而，模型模拟预测，在未来几个世纪内，南极洲释放的淡水和冰的体积可能至少是格陵兰岛的十倍。该项目的智力价值来自于它能够在南极的物理系统（冰盖动态、淡水排放和冰山崩解）与全球气候之间建立联系。PI（首席研究员）将使用海洋，冰山，冰盖和气候模型的组合来评估海洋环流和气候对冰盖融化增加的敏感性。这项研究的结果将有助于确定容易崩溃的冰盖区域以及海洋区域，其中显着的淡水化将对气候产生相当大的影响，并有助于指导观测监测系统的部署，该系统能够在冰和淡水排放开始接近能够破坏海洋环流和全球气候的水平时向我们发出警告。该项目将支持和培训两名研究生，每个PI将参与当地中小学，做演讲，指导科学博览会项目，并为课程开发做出贡献。一个新颖的，基于网络的，互动的，冰冻圈学习工具将被开发出来，以帮助使学童更加意识到极地地区在全球气候中的重要性，这个软件将在麻省大学STEM教育研究所组织的半天研讨会上介绍给科学教师。最近使用大陆冰盖/大陆架模型进行的数值模拟显示，在未来50-300年内（根据IPCC RCP（政府间气候变化专门委员会，代表性浓度路径）未来变暖情景的全部范围），南极冰盖退缩的速度可能比以前预测的更快，更大。大量的冰和淡水释放到南大洋将如何影响全球海洋环流和气候，目前还没有准确的评估。这部分是因为以前的模型模拟太粗糙，无法准确地解决狭窄的沿海边界流，陆架断裂，锋面和中尺度涡旋，这些对于逼真地模拟海洋中的淡水输送都非常重要。在这个奖项中，未来的淡水排放和南极冰山崩解的预测将被用来迫使一个高分辨率的涡旋分辨海洋模型（MITgcm）耦合到一个新的冰山模块和一个完全耦合的全球气候模型（CCSM 4）。高分辨率海洋/冰山模拟将确定中尺度涡旋在淡水输送中的作用，并对淡水如何平流输送到远场位置，包括北大西洋深水形成地点提供新的见解。这些模拟将提供有关冰锋和接地线附近的地下温度和海洋环流变化的详细信息。一套随附的完全耦合气候模式模拟（NCAR CCSM 4）将确定由高纬度南大洋淡水强迫增加引发的气候系统的数十年至百年变化。将特别注意大西洋经向翻转环流（AMOC），风应力，海冰形成和全球温度的强度变化。通过这样做，该项目将更准确地确定南极系统的变化是否可能在不久的将来引发全球气候的突然和潜在的灾难性变化。

There is compelling historical evidence that the West Antarctic Ice Sheet (WAIS) is vulnerable to rapid retreat and collapse. Recent observations, compared to observations made 20-30 years before, indicate that both ice shelves (thick ice with ocean below) and land ice (thick ice with land below), are now melting at a much faster rate. Some numerical models suggest that significant ice retreat may begin within many of our lifetimes, starting with the abrupt collapse of Pine Island and Thwaites Glaciers in the next 50 years. This may be followed by retreat of much of the WAIS and then the collapse of parts of the East Antarctic ice sheet (EAIS). This research project will assess the extent to which global ocean circulation and climate will be impacted if enormous volumes of fresh water and ice flow into the Southern Ocean. It will establish whether a rapid collapse of WAIS in the near-future poses any significant threat to the stability of modern-day climate and human society. This is a topic that has so far received little attention as most prior research has focused on the response of climate to melting the Greenland ice sheet. Yet model simulations predict that the volumes of fresh water and ice released from Antarctica in the next few centuries could be up at least ten-times larger than from Greenland. The Intellectual Merit of this project stems from its ability to establish a link between the physical Antarctic system (ice sheet dynamics, fresh water discharge and iceberg calving) and global climate. The PIs (Principal Investigators) will assess the sensitivity of ocean circulation and climate to increased ice sheet melt using a combination of ocean, iceberg, ice sheet and climate models. Results from this study will help identify areas of the ice sheet that are vulnerable to collapse and also regions of the ocean where a significant freshening will have a considerable impact on climate, and serve to guide the deployment of an observational monitoring system capable of warning us when ice and fresh water discharge start to approach levels capable of disrupting ocean circulation and global climate. This project will support and train two graduate students, and each PI will be involved with local primary and secondary schools, making presentations, mentoring science fair projects, and contributing to curriculum development. A novel, web-based, interactive, cryosphere learning tool will be developed to help make school children more aware of the importance of the Polar Regions in global climate, and this software will be introduced to science teachers at a half day workshop organized by the UMass STEM Education Institute. Recent numerical simulations using a continental ice sheet/shelf model show the potential for more rapid and greater Antarctic ice sheet retreat in the next 50-300 years (under the full range of IPCC RCP (Intergovernmental Panel on Climate Change, Representative Concentration Pathways) future warming scenarios) than previously projected. Exactly how the release of enormous volumes of ice and fresh water to the Southern Ocean will impact global ocean circulation and climate has yet to be accurately assessed. This is in part because previous model simulations were too coarse to accurately resolve narrow coastal boundary currents, shelf breaks, fronts, and mesoscale eddies that are all very important for realistically simulating fresh water transport in the ocean. In this award, future projections of fresh water discharge and iceberg calving from Antarctic will be used to force a high resolution eddy-resolving ocean model (MITgcm) coupled to a new iceberg module and a fully-coupled global climate model (CCSM4). High resolution ocean/iceberg simulations will determine the role of mesoscale eddies in freshwater transport and give new insight into how fresh water is advected to far-field locations, including deep water formation sites in the North Atlantic. These simulations will provide detailed information about subsurface temperatures and changes in ocean circulation close to the ice front and grounding line. An accompanying set of fully coupled climate model simulations (NCAR CCSM4) will identify multidecadal-to-centennial changes in the climate system triggered by increased high-latitude Southern Ocean freshwater forcing. Particular attention will be given to changes in the strength of the Atlantic Meridional Overturning Circulation (AMOC), wind stress, sea ice formation, and global temperatures. In doing so, this project will more accurately determine whether abrupt and potentially catastrophic changes in global climate are likely to be triggered by changes in the Antarctic system in the near-future.