The Challenge of Non-Stationary Feedbacks in Modeling the Response of Debris-Covered Glaciers to Climate Forcing

Abstract

Ongoing changes in mountain glaciers affect local water resources, hazard potential and global sea level. An increasing proportion of remaining mountain glaciers are affected by the presence of a surface cover of rock debris, and the response of these debris-covered glaciers to climate forcing is different to that of glaciers without a debris cover. Here we take a back-to-basics look at the fundamental terms that control the processes of debris evolution at the glacier surface, to illustrate how the trajectory of debris cover development is partially decoupled from prevailing climate conditions, and that the development of a debris cover over time should prevent the glacier from achieving steady state. We discuss the approaches and limitations of how this has been treated in existing modeling efforts and propose that “surrogate world” numerical representations of debris-covered glaciers would facilitate the development of well-validated parameterizations of surface debris cover that can be used in regional and global glacier models. Finally, we highlight some key research targets that would need to be addressed in order to enable a full representation of debris-covered glacier system response to climate forcing.

Revisiting glacier mass-balance sensitivity to surface air temperature using a data-driven regionalization

“…Limitations of our results are associated with the fact that at this global scale we cannot yet account for the impact of particular features of the monitored glaciers that may affect mass-balance sensitivity. For instance, supraglacial debris may decouple them from regional climatic conditions (Nicholson and others, 2021; Rounce and others, 2021) and thus impact mass balance. Therefore, future refinement of our analysis may include merging the global glacier inventory with recently published databases on debris cover (Herreid and Pellicciotti, 2020) to then account for that variable in the clustering in order to reassess our classification.…”

Quantifying Supraglacial Debris‐Related Melt‐Altering Effects on the Djankuat Glacier, Caucasus, Russian Federation

“…After plotting the obtained melt ratios against the debris thickness itself, values for the critical (h c d ) and characteristic debris thickness (h * d ) could be assigned to the debris thickness that exhibited a value for the melt ratio closest to 1 and 0.37 respectively. The effective debris thickness (h (Anderson & Anderson, 2016;Nicholson et al, 2021;Rounce et al, 2021).…”

“…The effective debris thickness ($${h}_{d}^{e}$$) and the associated maximum melt enhancement factor ($${f}_{d}^{e}$$) were determined by locating the maximum of a polynomial function through all values between h d = 0 m and h d = $${h}_{d}^{c}$$. To then fit an equation to the Østrem curve itself, we used a linear equation for values of $${h}_{d}\le {h}_{d}^{e}$$ (between points [0,1] and [$${h}_{d}^{e}$$, $${f}_{d}^{e}$$]), and a reciprocal equation for $${h}_{d} > {h}_{d}^{e}$$, which has been shown to provide the optimal fit for an Østrem curve (Anderson & Anderson, 2016; Nicholson et al., 2021; Rounce et al., 2021).…”

Be‐10 Dating of Ice‐Marginal Moraines in the Khumbu Valley, Nepal, Central Himalaya, Reveals the Response of Monsoon‐Influenced Glaciers to Holocene Climate Change

“…However, a limitation of such remote-sensing observations is that they represent a relatively short timescale (decades) compared to the response times of mountain glaciers to climatic forcing (centuries) (Hambrey et al, 2008). Understanding the processes that affect how glaciers have responded to climate change through the Holocene (∼11 ka to present) is required to identify the drivers of longer-term change and constrain projections of future glacier evolution (Nicholson et al, 2021;Owen et al, 2009;Rowan et al, 2015). 0.4 ± 0.1 ka (Murari et al, 2014;Saha et al, 2018).…”