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 the analysis of current and future changes. In the recent geological past changes in land ice and thermal expansion from increased temperatures are the dominant reasons of sea level rise. The last time the Earth was 2 °C warmer than the pre-industrial temperatures, sea levels were at least higher than present. This was during the last interglacial, when the earth warming was caused by slow changes in the orbital forcing. The warming was sustained over a period of thousands of years and the magnitude of the rise in sea level implied a large contribution from the Antarctic and Greenland ice