Atmospheric warming and enhanced melting of glaciers is already resulting in changes in the glacial contribution to run-off in mountain basins around the world. The enhanced melting of glaciers leads at first to increased run-off and discharge peaks and an increased melt season, while in the longer time frame glacier wasting can be so severe that it results in decreased run-off. Glacier basins with a decreasing run-off trend have been observed in south-central British Columbia, at low elevations in the Swiss Alps and in the central Andes of Chile, which is probably a combined effect of reduced melt from seasonal snow cover as the snow line rises, and relevant glacier area losses. In contrast, significant run-off increases are reported in Alberta, north-western British Columbia and Yukon in Canada, in highly glacierized basins in the Swiss and Austrian Alps, the Tianshan Mountains and Tibet in central Asia and in the tropical Andes of Peru. The run-off increase within these basins is closely related to observed temperature rise, indicating that there is an unequivocal signal of enhanced glacier melting under the present warming trends. In future warming scenarios, glacier run-off should start to decrease even in high-altitude basins, affecting water availability. Copyright (C) 2008 John Wiley & Sons, Ltd.