As shown in Table 1, approximately 33℃ of the atmospheric greenhouse-effect is brought by the downward infrared-radiation energy (approx. 155 W/m2) coming from the greenhouse-effect gasses in the atmosphere. About two thirds of the energy is from water including as water vapor in the atmosphere, and only a third is owed to the carbon dioxide (CO2) which is being the global issue. The difference between the impacts of the two types of gasses is more or less related to the difference in absorptivity in the infrared-radiation range, but major factors are the difference in abundance between the two, as follows.
Water Vapor in Atmosphere： 12,400 billion ton
Carbon Dioxide in Atmosphere： 2,628 billion ton
Therefore, water existing in atmosphere (i.e., water vapor) is the leading component for the atmospheric greenhouse-effect that plays a major role to maintain the temperature within the suitable range (0 to 40℃) for lives near the surface of the earth.
Nonetheless, neither increase nor decrease of water vapor in the atmosphere is the issue for the present global warming. This is because the amount of water vapor in the air is a function of the air temperature, and so determined as a result of a change in the temperature. On the other hand, the concentration of carbon dioxide keeps rising along with the massive consumption of fossil fuels by human beings, directly enhances the atmospheric greenhouse-effect, and raises the air temperature. This is why it draws the attention from all over the world.
2) Function of Water to Relax Climatic Conditions
Water has considerably great specific heat and latent heat of vaporization, as shown below. Because of such characteristics, it takes relatively long to warm up or cool down water. When water changes its phase (liquid ←→ vapor), huge heat energy is involved, where energy is actively transferred by formation, advection, or condensation of vapor,
Specific heat of water： 4,218 JK-1 kg-1 = 1.0 cal/ (℃･g)
