Glaciers are defined as a large mass of perennial ice of atmospheric origin generally moving slowly on land over a long period.

About 75% of the world’s entire natural freshwater is contained within ice sheets and glaciers. However 97% is not considered to be a water resource as it is inaccessible, located in the Antarctic, Arctic and Greenland ice sheets.

Land-based glaciers and permanent snow and ice cover approximately 680,000 km2 and are critical to many nations’ water resources.

Between 1980 and 2001, the thickness of 30 major mountain glaciers decreased by an average of 6 metres.
During the last century, land-based and mountain glaciers worldwide have been retreating and thinning, and this decline has considerably accelerated during recent years. The mean mass balance decrease that took place during the period 1990–1999 was 3 times greater than that of the previous decade.

Glacial ice often appears blue when it has become very dense. Years of compression gradually make the ice denser over time, forcing out the tiny air pockets between crystals. When glacier ice becomes extremely dense, the ice absorbs all other colours in the spectrum and reflects primarily blue, which is what we see. When glacier ice is white, that usually means that there are many tiny air bubbles still trapped in the ice.

During the last ice age, when glaciers covered almost one-third of the land the sea level was about 120 meters lower than it is today.

If all land ice melted, sea level would rise approximately 70 metres worldwide. Almost 90% of an iceberg is below water — only about 10% emerges above water.

The Kutiah Glacier in Pakistan holds the record for the fastest glacial surge. In 1953, it raced more than 12 Km in three months, averaging about 112 metres per day.

Between 1962 and 2000 the Kilimanjaro in Tanzania lost approximately 55% of its glaciers.

Information from:
the 2nd United Nations World Water Development Report, ‘Water, a shared responsibility’
the ‘International Glossary of Hydrology
the United Nations Statistics Division Environmental Glossary
the United States Geological Survey (USGS) section ‘Glaciers and icecaps: Storehouses of freshwater
UNEP’s GEO Year Book 2003
UNEP’s Mt. Kilimanjaro Forests section
the National Snow and Ice Data Center website

Source: UNESCO Water Portal, August 2006