The energy balance of the Earth

A sunray reaches the earth’s surface after travelling for 150 million kilometres in 8 minutes. The solar energy received by the earth amounts to 170,000 TW approximately (the unit of measurement equivalent to 1012 watts, used to measure solar energy). 50,000 TW are reflected by the top layers of the atmosphere, 30,000 are absorbed by the atmosphere and 90,000 TW reach the earth’s surface. A big part of them is reflected (by water, for example) or absorbed. A small part is transformed. 400 TW make seawater evaporate and transform it into clouds, 370 TW activate the wind and 80 TW are transformed by the plant’s photosynthesis into chemical energy. The 30,000 TW absorbed by the atmosphere and 90,000 reaching the earth’s surface are transformed into infrared radiations towards the space. Thus, the energy balance remains constant, like the temperature of the earth’s atmosphere and surface. The greenhouse effect, i.e. the natural phenomenon heating the bottom layers of the atmosphere, which normally makes human existence possible, has been lately increasing due to certain human activities often leading to catastrophic effects (i.e. climate changes).

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