The earth's temperature is rising - probably as a result of the increasing greenhouse effect that traps the heat inside the atmosphere. This means that the glaciers and the two large icecaps on Greenland and the Antarctic are beginning to melt. When the ice melts, the water starts flowing into the oceans and makes them rise.
In addition, the water of the oceans expands when heated. This means that the total volume of the water increases and contributes to further adding to the rise of the oceans.
The UN expert panel of climate scientists from all over the world concludes in its report from 2001 that the world's ocean level rose by between 10 and 20 cm during the 20th century. The water level is expected to increase by another 50 cm before 2100.
This may have a major impact on the lives of the millions of people living in low-lying areas around the world - as for instance, Holland or Bangladesh. Large parts of Holland are below or at the same level as the surface of the sea. They keep out the sea by means of dikes.
If the ocean rises by 45 cm, 11% of Bangladesh is expected to be flooded. Several small islands in the Pacific Ocean - the so-called Atolls - and in the Indian Ocean will be threatened by floods.