Explanation

Long-term (centennial to millennial) sea-level change is driven mainly by the melting of continental ice sheets in Greenland and Antarctica, which adds stored water to the oceans, together with thermal expansion of seawater. Melting icebergs and sea ice do not raise sea level because floating ice already displaces its own weight of water (Archimedes' principle). Atmospheric disturbances cause only short-term storm surges. The long-term cause is therefore the melting of ice sheets, option (D).