Latent heat of vaporization of water：
2.5 × 106 Jkg-1 = 597 cal/g (at 0℃)
Such physical properties specific to water substantially relax global climatic conditions, which, in turn, form large areas with suitable climate for lives to inhabit on the Earth.
To describe the mechanism clearly, I will briefly explain the energy balance of the Earth as follows. Figure 1 shows the total annual energy balance of the Earth. Assuming the Earth's planetary albedo (= solar energy reflection coefficient) is 0.3, the planet earth and a unit area of the surface of the earth absorb solar energy per annum as follows：
absorption by the planet earth (Qsa) = 179 kcal
absorption by the surface of the earth (Qaa) = 118 kcal
The difference, 61 kcal is the energy absorbed and scattered in the earth atmosphere. Not all the energy absorbed by the surface of the earth are used in the climatic phenomena near the ground. Part of it is emitted into the atmosphere as infrared radiation (I). By subtracting the radiation, I, the energy source of the climatic phenomena near the ground, viz., the net radiation (Rn) can be obtained. It is expressed as follows：
Rn = Qa - I = 118 - 39 = 79 kcal (1)
This net radiation, 79 kcal is distributed as follows. Of the annual net radiation given to the surface of the earth, 83.5% is used to evaporate water from the surface of the watery planet, whereas 16.5% is used to transfer heat from the earth's surface warmed by the solar radiation to the cooler atmosphere.
Water evaporation (lE) = 66 kcal
Heat transfer into atmosphere (P) = 13 kcal
From these, the Bowen ratio, which characterizes the heat energy distribution on the surface of the earth, becomes as follows：
P/lE = 13/66 ≒ 0.19 (2)
Therefore, the overall climatic conditions on the Earth can be regarded as moist (humid) and suitable for plant production, thus, inhabitation of lives.
