Figure 8. Global water reservoirs, fluxes, and turnover times. Major reservoirs are underlined, pool sizes are given in 103 km3, and fluxes are given in km3 yr-1. Pool sizes expresed as percentages of the total water budget are given in parentheses.

Water is present on Earth in three phases, solid, liquid, and gas, and all of these phases are present at some place in the Earth's major water reservoirs. The ocean is the largest water reservoir, with over 97% of the Earth's water, followed by the glacial reservoir with 2%. Both have turnover times of ~10,000 years. Although only slightly larger than the river reservoir, water in the atmosphere, which accounts for only 0.0009% of the total budget, plays a very important role in maintaining Earth' s h abitability. Water vapor is the most important greenhouse gas, and is responsible for some 30 íC of greenhouse warming. In addition, water's unusually high heat capacity and latent heats of vaporization and fusion play an important role in heat storage and transport. All phases of atmospheric water play important roles in the Earth's radiation budget. Atmospheric processes are responsible for transporting water from the ocean to land.