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2. Global Environment and Water

 

Recent valuation says that there is approximately water of 1.35 〜 1.37 billion km3 on the Earth, 97% of which fills seas (area of approx. 36.1 billion ha) with the average depth of 3,700m. This makes the Earth appear to be a deep blue planet of water, and so different from the other planets in the space.

So, the water should be the major factor that made the Earth a planet of lives, and has fostered the human race, the mysterious species. This chapter will briefly explain how the existence of water is related to the formation of global environment which allow lives in it.

 

1) Greenhouse Effect and Water Vapor in Atmosphere

By a simple balance equation of radiation energy, the temperature near the surface of the Earth without atmosphere, even with the current solar constant (= 1,367 W/m2 = 1.96 cal/ (cm2 ・ min)), can be obtained as follows (e.g., ref. Ogura 1997):

The temperature of the "naked" Earth: -18℃

In the meantime, by processing meteorological station's data that cover the surface of the Earth, the temperature near the surface of the Earth surrounded by atmosphere as it is now is as follows:

The temperature of the actual Earth: +15℃

From these two values, we can see that the current Earth surrounded by the thick atmosphere is kept 33℃ warmer than the assumed "naked" Earth. This is due to the greenhouse effect of the earth's atmosphere. Therefore, lives are considerably owed to this effect that maintain the temperature condition near the ground suitable for organisms to inhabit. Although the greenhouse effect tends to be viewed with hostility today due to its relationship with the global warming, it stems from the worries that the human activities for production may lead the greenhouse effect faster than the pace that the natural ecosystems and human society can conform to.

 

 

 

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