The hydrological cycle

Hydrological Cycle (Water Cycle): The continuous movement of water on the land, in the atmosphere and in the oceans.

The hydrological cycle is said to be a closed system because water can not be added or lost. Although water can not be added or lost it can be found in different states and in different locations. Despite the planet being covered in water, the vast majority is sea water (97.5%). Of the remaining 2.5% the majority is held in glaciers and ice sheets. Only a very small amount of the world's water is easily accessible in rivers and lakes (0.00069%).
Because of rising global temperatures the storage of water is changing. This is particularly true of water held as ice either as permafrost or in giant ice sheets and ice shelves.

Permafrost: Ground that is permanently frozen. For permafrost to exits the ground temperature must be below freezing for the whole year, Permafrost contains large amounts of methane which is released when it melts. Glacier: A slow moving river of ice ages. many of the world's glaciers are melting. The melting of glaciers at their snouts is known as ablation. Ice sheet: Also known as a continental glacier, ice sheets are areas of ice over 50,000 square kilometres found on land. The world's only ice sheets are found on Antarctica and Greenland. Iceberg: A large piece of ice that has broken off a glacier or ice shelf. 90% of icebergs are submerged underwater Ice shelf: Thick floating platforms of ice. Ice shelves are between 100, and 1,000m thick Sea ice: Frozen sea water. Seas like the Baltic Sea freeze during winter.

Because ice shelves and icebergs already make up part of the ocean's volume, their melting does not contribute to rising sea levels. However, because ice sheets are found on land, their melting does contribute to rising seal levels. In addition because the density of liquid water is greater than frozen water, as icebergs and ice shelves melt, they do not take up a grater volume of space. The melting of ice sheets will cause eustatic sea levels changes. This is a global rise in the level of the sea. It is possible for the height of the land to change relative to the sea (e.g. rebound from last ice age). These local changes in the height of the land are known as isostatic sea level changes. As well as melting ice sheets and glaciers, it must also be remembered that global warming causes thermal expansion i.e. the density of water reduces and causes an increase in the volume of water and therefore sea levels.

Greenland ice loss accelerating - BBC article

Some Effects of Sea Level Changes and Global Warming	Related article
Loss of island nations	First island lost due to rising sea levels - Al Jazeera article Maldives cabinet to hold underwater meeting - BBC article New York set to be big loser as sea levels rise - BBC article
Methane release from melting permafrost	Melting Siberian bogs release methane - BBC article
Loss of biodiversity	Polar bears die as ice shelf melts - Times article
Cost of protection	Cost of protection - two cities compared - BBC article
Climate refugees	Bangladesh climate refugees - BBC article

For more information on problems and solutions to global warming go to: Atmosphere and change
As with most things, there are some advantages that global warming and the melting of ice sheets/shelves will bring. For example:

• The Arctic will become navigable all year
• Resources (fish and oil) under the Arctic will become accessible.
• Heating bills will reduce and therefore use of energy.
• There will be less deaths from the cold.
• More land can be used for agricultural production.
• Permafrost may release new supply of freshwater.