Observational evidence indicates that a number of glaciers have lost mass in the past. Given that glaciers are highly impacted by the surrounding climate, human-influenced global warming may be partly responsible for mass loss. However, previous research studies have been limited to analyzing the past several decades, and it remains unclear whether past glacier mass losses are within the range of natural internal climate variability. Here, we apply an optimal fingerprinting technique to observed and reconstructed mass losses as well as multi-model general circulation model (GCM) simulations of mountain glacier mass to detect and attribute past glacier mass changes. An 8,800-year control simulation of glaciers enabled us to evaluate detectability. The results indicate that human-induced increases in greenhouse gases have contributed to the decreased area-weighted average masses of 85 analyzed glaciers. The effect was larger than the mass increase caused by natural forcing, although the contributions of natural and anthropogenic forcing to decreases in mass varied at the local scale. We also showed that the detection of anthropogenic or natural influences could not be fully attributed when natural internal climate variability was taken into account.

Abstract:We developed a monitoring system for deriving outlines of mountain glaciers and ice caps (MG&IC) at a 30 m horizontal resolution from Landsat Thematic Mapper (TM) and Landsat Enhanced Thematic Mapper plus (ETM+). Location and area information at 30 m resolution was obtained using a band ratio (TM4/TM5) and a threshold value of TM3 with a 9 by 9 pixel average filter. The total area and number of MG&IC were 449482 km 2 and 414258, respectively. The glacier outlines were similar to previous satellite-derived products for different regions. Although the derived glacier area was similar to previous estimates at regional scales, it was overestimated in some parts of Scandinavia where available satellite images are limited and only snowy season images can be used, and was underestimated in the western Himalayas and Caucasus where the glacier outlines are derived with difficulty from satellite images because of the effect of debris cover. Our system to monitor MG&IC has potential application in global hydrological and land-surface models and estimates of global sea-level rise.

Mountain glaciers are one of key elements to indicate current climate change considering their contribution to sea-level rise and to water resource change through regional hydrological processes. This study estimated the area and location of tropical mountain glaciers in Bolivia using satellite imagery. Previous studies have produced datasets of global glacier information, but the area/location information of mountain glaciers in Bolivia is not stored in those datasets due to limited field measurement data. In this study, we developed a couple of satellite remote sensing measurement methods so that the area/location information of tropical mountain glaciers in Bolivia was obtained at a country-wide scale for the first time.