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，南极西部冰盖（WAIS）很容易迅速退缩和崩塌。与20-30年前的观测结果相比，最近的观测结果表明，冰架（下面有海洋的厚冰）和陆冰（下面有陆地的厚冰）现在都在以更快的速度融化。一些数值模型表明，在我们许多人的有生之年，从未来50年松岛冰川和思韦茨冰川的突然崩塌开始，冰的大规模退缩可能会开始。随之而来的可能是大部分西南冰原的退缩，然后是南极东部冰盖（EAIS）的部分崩塌。这个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多大程度的影响。它将确定在不久的将来WAIS的迅速崩溃是否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，在接下来的几个世纪里，从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。这个项目的知识价值在于它能够建立南极物理系统（冰盖动力学、淡水排放和冰山崩解）与全球气候之间的联系。pi（首席调查员）将综合运用海洋、冰山、冰盖和气候模型，评估海洋环流和气候对冰盖融化加剧的敏感性。这项研究的结果将有助于确定冰盖易崩塌的区域，以及海洋中显著变新鲜将对气候产生重大影响的区域，并有助于指导部署观测监测系统，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，每位PI将参与当地的中小学，进行演讲，指导科学展览项目，并为课程开发做出贡献。一种新颖的、基于网络的、互动的冰冻圈学习工具将被开发出来，以帮助学校的孩子们更多地意识到极地地区在全球气候中的重要性，该软件将在麻省理工大学STEM教育研究所组织的为期半天的研讨会上介绍给科学教师。最近使用大陆冰盖/冰架模式的数值模拟表明，在未来50-300年（在IPCC RCP（政府间气候变化专门委员会，代表性浓度路径）未来变暖情景的全范围下），南极冰盖退缩的速度和幅度可能比以前预估的更快和更大。向南大洋释放大量冰和淡水究竟会对全球海洋环流和气候产生怎样的影响，目前还没有得到准确的评估。这在一定程度上是因为以前的模式模拟过于粗糙，无法准确地解决狭窄的海岸边界流、大陆架断裂、锋面和中尺度涡流，而这些对于实际模拟海洋中的淡水运输都非常重要。在本奖项中，未来对南极淡水排放和冰山崩解的预估将用于强制建立一个高分辨率漩涡分辨海洋模式（MITgcm），该模式与一个新的冰山模块和一个完全耦合的全球气候模式（CCSM4）相耦合。高分辨率的海洋/冰山模拟将确定中尺度漩涡在淡水运输中的作用，并为淡水如何平流到远场位置（包括北大西洋的深水形成地点）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。伴随的一套完全耦合的气候模式模拟（NCAR CCSM4）将确定由高纬度南大洋淡水强迫增加引发的气候系统几十年到百年的变化。将特别关注大西洋经向翻转环流（AMOC）强度的变化、风应力、海冰形成和全球温度。通过这样做，该项目将更准确地确定在不久的将来，南极系统的变化是否可能引发全球气候的突变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.