Since glaciers are essentially frozen snow, the water contained in them is fresh water.
Most water on Earth is salt water, so it cannot be used for drinking or watering crops.
Very little of the Earth's water is fresh and most of it - more than three quarters - is stored in glaciers and ice caps.
This means that glacier ice is the largest reservoir of fresh water on Earth.
The more of this ice that melts, the more fresh water there is that flows into the oceans and becomes salt water.
What would happen if all the ice melted?
If global warming led to the melting of all polar ice caps, the ocean water level would rise by about 80 metres - this would mean that nearly all of Denmark and most of Northern Germany would be covered with water.
This is not likely to happen in the foreseeable future, but even a small rise in the sea water level could be disastrous for islands or regions that lie just above or even below sea level.
The consequences of large-scale melting are difficult to assess. Scientists are working hard on this subject.