Mountain glaciers and ice-caps are often nicknamed ‘nature's thermometers’. Because of their relatively small size and high mass turnover rates, they show a rapid response to changes in the climate, and are one of the most visible indicators of a changing climate. Retreat and shrinkage of glaciers have been globally observed over the last century, and comes with profound societal, economic and environmental impacts, such as the release of freshwater into the oceans, glacier lake outbursts and landslides, and changes in local water availability for water consumption, hydro-electric power generation, agriculture and irrigation. The total amount of ice stored in glaciers and ice caps is only a small fraction (~1%) of the volume of the vast Greenland and Antarctic Ice Sheets. Yet, in the latest IPCC report, they were estimated to be the single largest land contributor to sea level rise in the 20th century, accounting for about 0.7 mm/y between 1901 and 1990. Until the mid-2000s, such estimates were mainly based on extrapolation of a limited number of in situ observations of relatively small glaciers, often located in easily accessible locations with a maritime climate, which comes with large uncertainties. The advent of satellite remote sensing has led to a leap forward in our understanding of the state of the cryosphere as it provides regular, near-global coverage of the Earth's glaciated regions. In this Special Issue, we invite contributions focusing on recent and upcoming advances in the application of satellite remote sensing to monitoring changes in the state of the Earth's mountain glaciers and ice caps. This excludes the main ice sheets of Antarctica and Greenland, but we do welcome studies focusing on their peripheral glaciers and ice caps, including the Antarctic Peninsula. Potential topics include, but are not limited to: variations in the volume and mass of glacier regions from gravimetry, altimetry, photogrammetry, etc. changes in their extent and surface properties (such as surface albedo) changes in the flow behavior of glacier regions, e.g., surface velocity and discharge first results from recently launched satellites (e.g., ESA's Sentinels) and the potential of upcoming missions (e.g., ICESat-2, GRACE-FO) multi-platform merging and the combination of satellite observations with historical data sources integration and assimilation of satellite remote sensing data into Earth system models novel applications of data processing, such as machine learning and “big data” analysis@en

Glaciers outside of the ice sheets are known to be important contributors to sea level rise. In this work, we provide an overview of changes in the mass of the world's glaciers, excluding those in Greenland and Antarctica, between 2002 and 2016, based on satellite gravimetry observations of the Gravity Recovery and Climate Experiment (GRACE). Glaciers lost mass at a rate of 199 ± 32 Gt yr ⁻¹ during this 14-yr period, equivalent to a cumulative sea level contribution of 8 mm. We present annual mass balances for 17 glacier regions, that show a qualitatively good agreement with published estimates from in situ observations. We find that annual mass balance varies considerably from year to year, which can in part be attributed to changes in the large-scale circulation of the atmosphere. These variations, combined with the relatively short observational record, hamper the detection of acceleration of glacier mass loss. Our study highlights the need for continued observations of the Earth's glacierized regions.

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