The document discusses the melting of glaciers due to global warming and the problems that this causes. Glaciers around the world, including the large ice sheets in Antarctica and Greenland, have been shrinking and retreating in recent decades. This melting is accelerated by rising global temperatures. The shrinking of glaciers threatens water supplies and will displace millions of people as sea levels rise. Scientists use various techniques like satellite observations, aerial surveys, and satellite gravimetry to measure changes in glacier mass and confirm that ice loss is increasing over the long term.