Global warming raises ocean levels at an accelerating pace, currently on average about three millimetres per year. The reasons for this are the thermal expansion of sea water and the melting of glaciers. It is estimated that by the end of this century, ocean levels will rise at least about 20 centimetres. The highest estimates are nearly two metres.
There is, however, great regional variation in the rise, for reasons such as the uneven warming of seas, changes in Earth's gravity field, and changes in the circulation of seas.