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.
Water distribution on Earth a globally significant amount of water. "Saline" groundwater is seldom considered except when evaluating water quality in arid regions. The remainder of the Earth's water constitutes the planet's "fresh water" resource. Typically, fresh water is defined as water with a salinity of "less than 1 percent that of the oceans" - i.e. below around 0.35‰. Water with a salinity between this level and 1‰ is typically referred to as "marginal water" because it is marginal for many uses by humans and animals. The ratio of salt water to fresh water on Earth is around 40 to 1. The planet's fresh