There are a few important processes that cause observed sea level rise. In order, with IPCC estimates on the magnitude:

- The ocean expands as it warms, which is the single largest contributor right now (1.1 mm/yr).

- Mountain glaciers are next, as they are very rapidly melting (0.76 mm/yr, with large uncertainties).

- Then Greenland, as mentioned by another poster (0.43 mm/yr).