Losing their Cool: are high-elevation heat exchanges warming Himalayan glaciers?

失去冷静：高海拔热交换会使喜马拉雅冰川变暖吗？

• 批准号: NE/Z000033/1
• 负责人: Duncan Quincey
• 金额: $ 107万
• 依托单位: University of Leeds
• 依托单位国家: 英国
• 项目类别: Research Grant
• 财政年份: 2024
• 资助国家: 英国
• 起止时间: 2024 至 无数据
• 项目状态: 未结题
• 来源: https://gtr.ukri.org/projects?ref=NE%2FZ000033%2F1
• 关键词: Losing; their; Cool; elevation; heat

We recently discovered that over half of the ablation area of one of the world's highest glaciers, Khumbu Glacier, Nepal, comprises ice that is at the melting point. Moreover, ice within the upper ablation area has warmed by 2-3 degrees Celsius over the last 40 years and is out of equilibrium with local climate. Combined, these observations indicate that high-elevation Himalayan glaciers are unexpectedly vulnerable to 21st Century climatic warming, and approaching a tipping point beyond which greatly accelerated mass loss will occur. However, the processes that determine ice temperatures within this region remain poorly understood, making projections of future glacier change uncertain.The overarching aim of Losing their Cool (LtC) is to investigate the physical interactions between the atmosphere and the glacier surface at high-elevation (>6,000 m a.s.l.), providing insight into the snow and firn processes that prescribe Himalayan ice temperatures for the first time. The working hypothesis is that melting and refreezing within the accumulation area is sufficiently effective to raise firn-layer temperatures by several degrees prior to ice formation. To test this, LtC will collect the first robust and sustained measurements of firn conditions from Khumbu Glacier's accumulation area in the Western Cwm of Mount Everest. We will drill and instrument 20-25 m-long boreholes at elevations of 6,000-6,800 m a.s.l. to measure englacial firn and ice temperatures over a two-year period. We will also use a 360 degree camera to image the interior of the boreholes to characterise firn density and quantify the magnitude and frequency of previous re-freezing events. We will install automatic weather stations at elevations where they do not already exist, and take samples from the cores for collaborators working in relevant fields (e.g. biogeochemistry). We will use these empirical data to calibrate, and then validate, a numerical model that can simulate both the energy fluxes driving warming at the surface, and the consequent subsurface meltwater flow and refreezing processes. This will enable us to isolate the impact of meltwater re-freezing on ice temperature, and determine the extent to which this changes in a warming climate. Finally, we will simulate the whole glacier system, and track the evolution of ice temperatures with distance downglacier, to assess the extent to which firn processes can account for the unexpectedly high temperatures we previously observed in the glacier ablation area, as well as yield improved forecasts of ice loss up to 2100.This work will provide new understanding of firn processes that are relevant for all glaciers within similar settings world-wide. In particular it will improve the way we represent ice stiffness and processes of ice flow in dynamic glacier models. It will resolve outstanding debates in the literature about the possibility of net mass loss at the world's highest elevations, and indicate the extent to which other glaciers within the Himalaya may also comprise unexpectedly warm ice. Our work will provide insights into a rarely observed cryospheric zone that can inform agenda-setting reports such as those produced by the Intergovernmental Panel on Climate Change, as well as addressing, directly and indirectly, several key Sustainable Development Goals. We will further provide evidence for supporting agencies such as UNDP, and the Nepalese government, to help prepare for, and mitigate against, a now inevitable change in meltwater supply as climatic changes continue to impact this region.

我们最近发现，世界上最高的冰川之一尼泊尔昆布冰川的消融面积有一半以上是处于熔点的冰。此外，在过去的40年里，消融区上部的冰已经升温了2-3摄氏度，与当地气候不平衡。综合起来，这些观察结果表明，高海拔喜马拉雅冰川意外地容易受到21世纪世纪气候变暖的影响，并接近一个临界点，超过这个临界点，将发生大大加速的质量损失。然而，对决定该地区冰温的过程仍知之甚少，使得对未来冰川变化的预测不确定。“降温”（LtC）的总体目标是调查高海拔（>6,000 m a.s.l.）大气和冰川表面之间的物理相互作用，提供了对雪和积雪过程的深入了解，这是第一次规定喜马拉雅山的冰温度。目前的假设是，在冰形成之前，堆积区内的融化和再冻结足以有效地将积雪层的温度提高几度。为了验证这一点，LtC将收集珠峰西部库姆冰川积累区的第一批可靠和持续的积雪状况测量数据。我们将在海拔6，000 - 6，800米的地方钻探20-25米长的钻孔并进行仪器测量。在两年的时间里测量冰内积雪和冰的温度。我们还将使用360度摄像机对钻孔内部进行成像，以确定积雪密度，并量化以前重新冻结事件的幅度和频率。我们将在尚不存在自动气象站的海拔高度安装自动气象站，并从岩心中采集样本，供相关领域（例如地球化学）的合作者使用。我们将使用这些经验数据来校准，然后验证，一个数值模型，可以模拟在地表驱动变暖的能量通量，以及随之而来的地下融水流和再冻结过程。这将使我们能够隔离融水重新冻结对冰温度的影响，并确定在气候变暖的情况下这种变化的程度。最后，我们将模拟整个冰川系统，并跟踪冰温度随冰川下降距离的演变，以评估积雪过程在多大程度上可以解释我们先前在冰川消融区观察到的意外高温，这项工作将提供对类似冰川内所有冰川相关的积雪过程的新认识，世界各地的设置。特别是，它将改善我们在动态冰川模型中表示冰刚度和冰流过程的方式。它将解决文献中关于世界最高海拔地区净质量损失可能性的悬而未决的争论，并表明喜马拉雅山脉内其他冰川也可能包含意想不到的温暖冰的程度。我们的工作将提供对一个很少被观察到的冰冻圈区域的深入了解，这些区域可以为政府间气候变化专门委员会等机构编制的报告提供信息，并直接和间接地解决几个关键的可持续发展目标。我们将进一步为联合国开发计划署和尼泊尔政府等支持机构提供证据，帮助他们做好准备，并减轻由于气候变化继续影响该地区而导致的融水供应不可避免的变化。