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.
Imperial and US customary measurement systems of Henry Cavendish, proposed the definition of the Fahrenheit scale be modified such that the temperature corresponding to the melting point of ice be 32 °F and the boiling point of water under standard atmospheric conditions be 212 °F. The British thermal unit (Btu) is defined as the heat needed to raise the temperature of one pound of water by one degree Fahrenheit. It was in use before 1859 as a unit of heat based on imperial units rather than the metric units used by the French—Clément-Desormes having defined the calorie in terms of the kilogram and degrees centigrade in