Sea level the warmer water expands. For at least the last 100 years, sea level has been rising at an average rate of about per year. Most of this rise can be attributed to the increase in temperature of the sea and the resulting slight thermal expansion of the upper of sea water. Additional contributions, as much as one-quarter of the total, come from water sources on land, such as melting snow and glaciers and extraction of groundwater for irrigation and other agricultural and human uses. Pilots can estimate height above sea level with an altimeter set to a defined barometric pressure.
Sea level rise literature found estimates for the Greenland ice sheet and its glaciers and ice caps, they were the largest contributor to the observed sea level rise from "land ice" sources (excluding thermal expansion), combined accounting for 71 percent, or 1.32 mm per year during the 2012–2016 period. Mountain glaciers include only a minor fraction of all water bound up in glaciers ice (<1%), compared to a bigger portion in Greenland and Antarctica (99%). Still, mountain glaciers have contributed appreciably to historical sea level rise and are set to contribute a smaller, but still significant fraction of sea level rise in the