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

Lead Research Organisation: University of Leeds
Department Name: Sch of Geography


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.


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