Why is sea level rising?

Global mean sea level has risen by roughly 20 centimetres since 1900, and the rate has accelerated to around 4 millimetres per year in recent years according to satellite measurements. Two main processes drive it: thermal expansion, since water takes up more space as it warms, and the addition of meltwater from mountain glaciers and the Greenland and Antarctic ice sheets. Melting sea ice, which already floats, adds very little. The IPCC projects further rises this century whose size depends strongly on future emissions. Rising seas increase coastal flooding, erosion and saltwater intrusion into farmland and drinking water.