Holocene glaciers have contributed to an abundance of unstable sediments in mountainous environments. In permafrost environments, these sediments can contain ground ice and are subject to rapid geomorphic activity and evolution under condition of a warming climate. To understand the influence of ground ice distribution on this activity since the Little Ice Age (LIA), we have investigated the Pierre Ronde and Rognes proglacial areas, two cirque glacier systems located in the periglacial belt of the Mont Blanc massif. For the first time, electrical resistivity tomography, temperature data loggers and differential global positioning systems (dGPS) are combined with historical documents and glaciological data analysis to produce a complete study of evolution in time and space of these small landsystems since the LIA. This approach allows to explain spatial heterogeneity of current internal structure and dynamics. The studied sites are a complex assemblage of debris-covered glacier, ice-rich frozen debris and unfrozen debris. Ground ice distribution is related to former glacier thermal regime, isolating effect of debris cover, water supply to specific zones, and topography. In relation with this internal structure, present dynamics are dominated by rapid ice melt in the debriscovered upper slopes, slow creep processes in marginal glacigenic rock glaciers, and weak, superficial reworking in deglaciated moraines. Since the LIA, geomorphic activity is mainly spatially restricted within the proglacial areas. Sediment exportation has occurred in a limited part of the former Rognes Glacier and through water pocket outburst flood and debris flows in Pierre Ronde. Both sites contributed little sediment supply to the downslope geomorphic system, rather by episodic events than by constant supply. In that way, during Holocene and even in a paraglacial context as the recent deglaciation, proglacial areas of cirque glaciers act mostly as sediment sinks, when active geomorphic processes are unable to evacuate sediment downslope, especially because of the slope angle weakness.
This contribution explores the internal structure of very small debris-covered glacier systems located in permafrost environments and their current dynamical responses to short-term climatic variations. Three systems were investigated with electrical resistivity tomography and dGPS monitoring over a 3-year period. Five distinct sectors are highlighted in each system: firn and bare-ice glacier, debris-covered glacier, heavily debris-covered glacier of low activity, rock glacier and ice-free debris. Decimetric to metric movements, related to ice ablation, internal deformation and basal sliding affect the glacial zones, which are mainly active in summer. Conversely, surface lowering is close to zero (−0.04 m yr −1 ) in the rock glaciers. Here, a constant and slow internal deformation was observed (c. 0.2 m yr −1 ). Thus, these systems are affected by both direct and high magnitude responses and delayed and attenuated responses to climatic variations. This differential evolution appears mainly controlled by (1) the proportion of ice, debris and the presence of water in the ground, and (2) the thickness of the superficial debris layer.
Since 1972, the United Nations Educational, Scientific and Cultural Organization (UNESCO) World Heritage Convention aims to identify and protect sites of Outstanding Universal Value for future generations. However, growing impacts of climate change are of the utmost concern for the integrity of many sites. Here, we inventory the glaciers present in natural World Heritage sites for the first time. We found 19,000 glaciers in 46 sites located all over the world. We analyze their recent evolution, current state, and project their mass change over the 21st century. Our results are based on a comprehensive review of the literature as well as a state-of-the-art glaciological model for computing glacier responses up to 2100. Illustrating the strong influence of CO 2 emission scenarios and human actions on future ice loss magnitude, we project the wastage of 33% to 60% of the 2017 cumulative ice volume of 12,000 km 3 of World Heritage glaciers by 2100. Furthermore, we expect complete glacier extinction in 8 to 21 of the investigated World Heritage sites until the end of the century, depending on the climate scenario. We suggest that World Heritage glaciers should be considered as analogs to endangered umbrella, keystone, and flagship species, whose conservation would secure wider environmental and social benefits at global scale. Plain Language SummaryThe World Heritage convention aims at protecting the Earth's outmost assets and commits humanity to transmit them to future generations. However, many World Heritage sites are affected by anthropogenic climate change. Here, we present the first study on the glaciers located within the natural World Heritage sites. We inventoried 19,000 World Heritage glaciers and projected their mass changes over the 21st century. The results emphasize that major glacier decline will occur in these iconic sites in future decades. Nevertheless, ice loss magnitude will vary by a factor of 2 according to CO 2 emission scenarios and thus human activities. This study points out how the conservation of World Heritage glaciers could serve as a leverage and a target to tackle the unprecedented issue of climate change. Glaciers are more than disappearing passive climatic indicators. They are key components of planetary ecosystems that influence global climate and sea level, as well as water fluxes, human activities, or biodiversity at the regional scale. The conservation of these iconic endangered features could thus mobilize global-scale conservation and climate mitigation benefits. In this context, we show how drastic reduction of emissions will rapidly curb melt rates and safeguard a large glacier volume on the long term.
ABSTRACT. Glacier response to climate forcing can be heterogeneous and complex, depending on glacier system characteristics. This article presents the decadal evolution of the Tsarmine Glacier (Swiss Alps), a very small and heavily debris-covered cirque glacier located in the Alpine periglacial belt. Archival aerial photogrammetry and autocorrelation of orthophotos were used to compute surface elevation, volume and geodetic mass changes, as well as horizontal displacement rates for several periods between 1967 and 2012. A GPR survey allowed us to investigate glacier thickness (15 m . This might be explained by the combined influence of debris cover, shadow, snow redistribution and permafrost conditions on this very small glacier.
Glacier shrinking and the development of postglacial ecosystems related to anthropogenic climate change is one of the fastest ongoing ecosystem shifts, with paramount ecological and societal cascading consequences globally (Huss et al., 2017; Milner et al., 2017; Cauvy and Dangles, 2019; IPCC, 2021). Yet, no complete spatial analysis exists to quantify or anticipate this major changeover (Ficetola et al., 2021; Zimmer et al., 2022). Here we model glacier responses to climate projections until 2100 and subglacial terrain to explore the ecological trajectory of all glaciated areas, outside the Antarctica and Greenland ice sheets. Depending on climate change magnitude, glaciers could lose less than one quarter to half of their area by 2100. Mainly composed of terrestrial, then marine and freshwater areas, deglaciated areas could range from the equivalent surface of Nepal to Finland. Ecological conditions in deglaciated areas will remain extreme in some regions, offering refuges for cold-adapted species, but become mild in others, favouring biogeochemical processes, primary productivity and generalist species. This unprecedented travel into the future of cold regions shows that glaciers and postglacial ecosystems have key roles to play to face climate change, biodiversity loss and freshwater scarcity. Less than a third of these vulnerable common goods, barely considered in nature conservation policies (IPBES, 2019), are located within protected areas. We therefore call to urgently enhance both climate change mitigation and the in-situ protection of these key ecosystems to secure their existence, functioning and values.
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