Suchergebnisse

The World's Glaciers and Ice Caps (GIC) contain a sea level rise (SLR) equivalent of about 0.4 m. Although their potential sea level contribution is small compared to Greenland (7.4 m) or Antarctica (58.3 m), the GIC are the largest contributor to global SLR at present. During the last 20 years, the GIC contributed 2.5 cm SLR vs 1 cm for Greenland and Antarctica. Rising global sea levels and posing a significant problem to society. Runoff from the melting GIC has an impact on the regional hydrology and freshwater supply. The latter is of great concern in highly populated regions such as Central Asia where it negatively affects economic activities and political stability. Defining consistent methodologies to monitor the state of GIC in these regions and reduce uncertainties regarding their specific ice mass loss and relative contribution to SLR is critical not only to science but to the public, policy development, and implementation. In this dissertation, we use available satellite and modeling techniques to estimate recent contribution to sea level rise by the ice-covered regions outside the two ice sheets during the last two decades. We estimate glacier mass balance employing: time-variable gravity measurements by the NASA GRACE mission, and satellite altimetry by the NASA ICESat and the ESA CryoSat-2 mission. These techniques are applied in key regions of the Arctic, where increasing atmospheric and ocean temperatures have led to accelerating glacier mass losses. In the second part of this work is focused on the glaciers High Mountains of Asia, the largest freshwater reservoir outside the Polar Regions. Here, we use a mixture of remote sensed observations and atmospheric models to characterize the effect of glacier mass loss on the water cycle of the Indus River Basin.This work helps improve our general understanding of the mechanisms driving current glaciers and ice caps mass change and its relative impact on freshwater availability and sea level rise during the next century.

The Arctic is thawing. In summer, cruise ships sail through the once ice-clogged Northwest Passage, lakes form on top of the Greenland Ice Sheet, and polar bears swim farther and farther in search of waning ice floes. At the opposite end of the world, floating Antarctic ice shelves are shrinking. Mountain glaciers are in retreat worldwide, unleashing flash floods and avalanches. We are on thin ice―and with melting permafrost's potential to let loose still more greenhouse gases, these changes may be just the beginning. Vanishing Ice is a powerful depiction of the dramatic transformation of the cryosphere―the world of ice and snow―and its consequences for the human world. Delving into the major components of the cryosphere, including ice sheets, valley glaciers, permafrost, and floating ice, Vivien Gornitz gives an up-to-date explanation of key current trends in the decline of ice mass. Drawing on a long-term perspective gained by examining changes in the cryosphere and corresponding variations in sea level over millions of years, she demonstrates the link between thawing ice and sea-level rise to point to the social and economic challenges on the horizon. Gornitz highlights the widespread repercussions of ice loss, which will affect countless people far removed from frozen regions, to explain why the big meltdown matters to us all. Written for all readers and students interested in the science of our changing climate, Vanishing Ice is an accessible and lucid warning of the coming thaw.

"Glaciers is a volume about the role glaciers play in our daily lives (often without us knowing), the risks posed to glaciers from natural and anthropogenic activity (including climate change and industrial pollution), and policies and practices that should be employed to protect this fundamental hydrological reserve"--

This project has received funding from the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation programme grant agreement No 772751, RAVEN, "Rapid mass losses of debris covered glaciers in High Mountain Asia". ; Ice cliffs play a key role in the mass balance of debris-covered glaciers, but assessing their importance is limited by a lack of datasets on their distribution and evolution at scales larger than an individual glacier. These datasets are often derived using operator-biased and time-consuming manual delineation approaches, despite the recent emergence of semi-automatic mapping methods. These methods have used elevation or multispectral data, but the varying slope and mixed spectral signal of these dynamic features makes the transferability of these approaches particularly challenging. We develop three semi-automated and objective new approaches, based on the Spectral Curvature and Linear Spectral Unmixing of multispectral images, to map these features at a glacier to regional scale. The transferability of each method is assessed by applying it to three sites in the Himalaya, where debris-covered glaciers are widespread, with varying lithologic, glaciological and climatic settings, and encompassing different periods of the melt season. We develop the new methods keeping in mind the wide range of remote sensing platforms currently in use, and focus in particular on two products: we apply the three approaches at each site to near-contemporaneous atmospherically-corrected Pléiades (2 m resolution) and Sentinel-2 (10 m resolution) images and assess the effects of spatial and spectral resolution on the results. We find that the Spectral Curvature method works best for the high spatial resolution, four band Pléaides images, while a modification of the Linear Spectral Unmixing using the scaling factor of the unmixing is best for the coarser spatial resolution, but additional spectral information of Sentinel-2 products. In both cases ice cliffs are mapped with a Dice coefficient higher than 0.48. Comparison of the Pléiades results with other existing methods shows that the Spectral Curvature approach performs better and is more robust than any other existing automated or semi-automated approaches. Both methods outline a high number of small, sometimes shallow-sloping and thinly debris-covered ice patches that differ from our traditional understanding of cliffs but may have non-negligible impact on the mass balance of debris-covered glaciers. Overall these results pave the way for large scale efforts of ice cliff mapping that can enable inclusion of these features in debris-covered glacier melt models, as well as allow the generation of multiple datasets to study processes of cliff formation, evolution and decline. ; Publisher PDF ; Peer reviewed

High thinning rates (up to −4.0±0.97 m a−1) have been measured at Campo de Hielo Patagónico Norte (CHN) or Northern Patagonia Icefield, Chile between 1975 and 2001. Results have been obtained by comparing a Digital Elevation Model (DEM) derived from regular cartography compiled by Instituto Geográfico Militar of Chile (IGM) based upon 1974/1975 aerial photographs and a DEM generated from Advanced Space-borne Thermal Emission and Reflection Radiometer (ASTER) satellite images acquired in September 2001. A complete cloud-free Landsat ETM+ satellite image mosaic acquired in March 2001 was used to update the available glacier inventory of the CHN, including all glaciers larger than 0.5 km2 (48 new glaciers). A new delineation of ice divides was also performed over the accumulation areas of glaciers sharing the high plateau where the existing regular cartography exhibits poor coverage of topographic information. This updated glacier inventory produced a total ice area for 2001 of 3953 km2, which represents a decrease of 3.4±1.5% (140±61 km2 of ice) with respect to the total ice area of the CHN in 1979 calculated from a Landsat MSS satellite image. Almost 62% of the total area change between 1979 and 2001 took place in glaciers located at the western margin of the CHN, where the maximum area loss was experienced by Glaciar San Quintín with 33 km2. At the southern margin, Glaciar Steffen underwent the largest ice-area loss (12 km2 or 2.6% of the 1979 area), whilst at the eastern margin the greatest area loss took place in Glaciares Nef (7.9 km2, 5.7% of the 1979 area) and Colonia (9.1 km2, 2.7% of the 1979 area). At the northern margin of the CHN the lower debris-covered ablation area of Glaciar Grosse collapsed into a new freshwater lake formed during the late 1990s. The areal changes measured at the CHN are much larger than previously estimated due to the inclusion of changes experienced in the accumulation areas. The CHN as a whole is contributing melt water to global sea level rise at rates ∼25% higher than previous estimates.

A consequence of melting Arctic ice caps is the commercial viability of the Northern Sea Route, connecting North-East Asia with North-Western Europe. This will represent a sizeable reduction in shipping distances and a decrease in the average transportation days by around one-third compared to the currently used Southern Sea Route. We examine the economic impact of the opening of the Northern Sea Route in a multi-sector Eaton and Kortum model with intermediate linkages. This includes a remarkable shift of bilateral trade flows between Asia and Europe, diversion of trade within Europe, heavy shipping traffic in the Arctic, and a substantial drop in traffic through Suez. These global trade changes are reflected in real income and welfare effects for the countries involved. The estimated redirection of trade has also major geopolitical implications: the reorganisation of global supply chains within Europe and between Europe and Asia, and the highlighted political interest and environmental pressure on the Arctic.