The Himalaya depend on glacier ice and snow melt for water supply, food security and energy production more than any other region in the world. In the headwaters of the Brahmaputra, recent climate records show an increase in temperature since the 1970s, a decrease in total precipitation, and a partial replacement of snowfall by rain. Consequently, many glaciers in the region are decaying. Rates of mass loss in the eastern Himalaya have been measured at –0.26 ± 0.13 m w.e. a-1 for the first part of this century and –0.40 ± 0.25 m w.e. a-1 for the period 1992 to 2008; across the wider Himalayan region glaciers are losing almost 13 gigatonnes of mass per year, equating to 0.035 mm per year of sea-level rise. Given the lag between atmospheric adjustment and glacier ice response, this trend is set to continue through coming decades irrespective of future climatic change. Modelled climate projections (CMIP5 scenarios) suggest that air temperature in the region will continue to rise at a rate of between 0.021 and 0.040 °C a-1 and annual precipitation will change within the range –8 to +15% until 2050. It is therefore critical, and timely, to provide robust analyses of likely glacier evolution to policy makers in the Himalayan region where demands on water resources are growing and glaciers provide a substantial proportion of river flow, particularly during the dry season.