A spectacular example of land subsidence due to mining (including oil and gas extraction) is the lowering of the sea bottom above the Ekofisk oil field in the North Sea. In 1984, significant subsidence (compared to the installation level in the '70's) had been discovered which amounted to 3.6 m by 1986.

In 1987, a huge operation was carried out in which six platforms were raised 6.5 m all at the same time (see Fig. 66 and Fig. 67). Enormous hydraulic cylinders were placed beside the steel legs to take the complete weight of the superstructure. The platforms were then raised after cutting the legs. Finally extension pieces of 6.5 m were mounted between platforms and legs.

Although still surrounded with great uncertainty, global warming induced by increased concentrations of the greenhouse gases, will give rise to climate change, sea level rise and changes in the behaviour of storms. Since these changes will have large effects on coastal areas, many studies have recently been started to estimate the impact on coasts throughout the world. Due to the uncertainties in the increase of greenhouse gases as well as their impact, various scenarios have been developed with high, best guess and low estimates for the sea level rise (see Fig. 68). Assessment studies are often based on sea level rises of the order of 0.5 to 1.0 m per century.