Sea levels are rising
The global average sea level rose by close to 20 centimetres between 1870 and 2007.
Sea levels rose at an average of 1.7 millimetres per year during the 20th century, and 3.4 millimetres per year from 1993 to 2007.
Factors in sea level rise
As water warms, it expands in volume.
This thermal expansion of the ocean is the major cause of sea level rise in the 20th century.
The other main contributors are the melting of glaciers and ice caps around the world, with smaller contributions from the melting of Greenland and Antarctic ice sheets.