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The hydrosphere is a generic term for all the water on Earth. It includes underground water, mobile and immobile surface water, and atmospheric water. 2.5% of global water is not salinated, and is generally referred to as fresh water. Of this, 68.9% is locked up in frozen ice or snow.

The Earth's oceans, land and atmosphere contain an estimated 1.4 × 106 km3 [1.4 × 1021 litres, or 1.4 billion billion tonnes] of water. The oceans contain 96.5% of the water, 2% is ice, and only 1% of global water is terrestrial, including the water in living organisms.

sea rise UK
An 80m sea rise, resulting from most of the ice and snow melting into the oceans, would leave many countries looking a lot different

Water is cycled around the globe through terrestrial surface flow and evaporation/precipitation through the atmosphere. The terrestrial ecosystem makes use of the water as it cycles through, and, except for long-term aquifer storage, water is relatively temporary in its residence in soil, groundwater, rivers and lakes.

People have often intervened in the natural hydrological cycle, building dams, irrigation systems and mining water from underground. People have also drained wetlands and changed river and estuary courses in their quest to control their habitat.

With climate change, water is a major factor in the changing world environment. More energy in the oceans and atmosphere is changing the proportion of water locked in perpetual ice and snow, and causing more precipitation, and rising sea levels. Since human civilisation has generally developed along water highways, along coasts and rivers, changes to the world's water system is having serious repercussions on the human way of life.

Water Storage in the Hydrosphere

Here is a list of water storages in the hydrosphere, and their approximate retention (or reservoir) times - the time a molecule is likely to be retained before re-entering the hydrocycle in another phase.

Water storage Retention time (years)
Polar ice caps 10k
Permafrost ice 10k
Oceans 2.5k
Groundwater 1.5k
Mountain glaciers 1.5k
Large lakes 17
Bogs (swamps) 5
Upper soil moisture 1
Atmospheric moisture 0.03
Rivers 0.04