How sensitive are mountain glaciers to climate change? Insights from a block model

Eviatar Bach,Valentina Radić,Christian Schoof

doi:10.1017/jog.2018.15

Eviatar Bach, Valentina Radić + Show 1 more

Open Access

https://doi.org/10.1017/jog.2018.15

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Abstract

ABSTRACTSimple models of glacier volume evolution are important in understanding features of glacier response to climate change, due to the scarcity of data adequate for running more complex models on a global scale. Two quantities of interest in a glacier's response to climate changes are its response time and its volume sensitivity to changes in the equilibrium line altitude (ELA). We derive a simplified, computationally inexpensive model of glacier volume evolution based on a block model with volume–area–length scaling. After analyzing its steady-state properties, we apply the model to each mountain glacier worldwide and estimate regionally differentiated response times and sensitivities to ELA changes. We use a statistical method from the family of global sensitivity analysis methods to determine the glacier quantities, geometric and climatic, that most influence the model output. The response time is dominated by the climatic setting reflected in the mass-balance gradient in the ablation zone, followed by the surface slope, while volume sensitivity is mainly affected by glacier size, followed by the surface slope.

Highlights

Despite comprising a small fraction of the world’s total ice volume, the majority of which is in the ice sheets of Greenland and Antarctica, mountain glaciers and ice caps are major contributors to ongoing sea-level rise (SLR)
Simple models of glacier evolution typically describe the glacier geometry using a small number of degrees of freedom, and reduce their dynamics to a statement of mass balance combined with a set of heuristic or empirical closures that reflect the mechanics of glacier flow and feedbacks between glacier geometry and surface mass balance
Using the regional equilibrium line altitude (ELA) distance (dr; Eqn (19)), we find that Antarctic and Subantarctic, Svalbard and Scandinavia (267, 322 and 326 m, respectively) are the most threatened by the complete disappearance of glaciers, while Alaska, South Asia West and Caucasus and Middle East are the least (1645, 1250 and 1074 m, respectively)

Summary

Introduction

Despite comprising a small fraction of the world’s total ice volume, the majority of which is in the ice sheets of Greenland and Antarctica, mountain glaciers and ice caps are major contributors to ongoing sea-level rise (SLR). The glacier contribution to SLR is projected to be in the range 0.07–0.17 m by the end of the 21st century, which is roughly a third of the total projected SLR (Radić and Hock, 2011). This can cause severe damage to small island states and coastal and low-lying areas (Wong and others, 2014). Current approaches to projecting glacier mass or volume changes on regional and global scales rely on relatively simple models of glacier evolution (Marzeion and others, 2012; Radić and others, 2014; Clarke and others, 2015; Huss and Hock, 2015). A key challenge for these simplified glacier flow models is to represent the effects of bed geometry, which is often poorly known for individual glaciers, and of surface mass balance, for which detailed information only exists for a handful of glaciers with longterm monitoring programs

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