evidence: Sea level is a measure of the average height of the surface of the sea. Like land, the surface of the ocean is not flat or uniform. But unlike land – for the most part – it can change in short order. [...] Global sea level has been rising over the past century, and we’ve seen the rate increase in recent decades. Global tidal records from 1900 to 1990 show an estimated 4- to 5-inch rise in global mean sea level. Then, in the 25 years from 1990 to 2015, this global tide gauge network showed global sea level rising 3 inches, agreeing with measures by satellite altimeters taken since 1992. Currently, sea level is rising about one-eighth of an inch per year but is projected to rise in the future. By 2100, sea levels may rise another 1 to 8 feet – that’s feet, not inches. [...] Global sea level is rising from two primary causes: the expansion of ocean water as it warms; and increased melting of land-based ice, like glaciers and ice sheets in Greenland and Antarctica and other "upland" areas.