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Some gases present in the atmosphere of the Earth are artificially introduced by human activities, although in little amounts and they can increase the natural greenhouse effect present in it, to maintain the average temperature of our atmosphere at about 15C.

The action of these gases is absorbing the thermal infrared (IR) radiactions reflected by the ground toward the sky and also reflecting again these radiations toward the ground (depending on their wavelenghts and on the gas species); in this way, heat accumulates in the low layers of the atmosphere (troposphere) like it happens in a greenhouse under the sun, where the greenhouse roofs have the same action of those gases in excess in our atmosphere.

These gases are; CO2 (CARBON DIOXIDE) the main responsible and the most abundant, CH4 (METHANE), N2O (NITROUS OXIDE, or NITROGEN PROTOXIDE).
Then, there are other gases, able to create the same effect like CFCs (ChloroFuoro Carbides) and O3 (OZONE); they are present in much minor amount, but the combined action ov N20, CH4 and CFCs is today nearly equal to that of CO2 alone.

We can examine the natural and human sources of these gases, the protagonists of the climatic drama (the global warming) that is maturing year by year.

CO2
Its concentration in the atmosphere is today of 370 ppm (parts per million) or 0.037% but, in 1860, just at the beginning of the industrial revolution in all Europe, Japan and North America, it was 288 ppm.
Its effect is also enhanced by its persistence in the atmosphere, variable between 50 and 200 year and by the drastic reduction of forests coverage on the whole planet in the same period that has decreased also forests ability to absorb CO2 and raised its permanence in the atmosphere.
CO2 is the classic product of our combustions of FOSSIL FUELS (OIL, COAL, NATURAL GAS) that are the main source, with a 75% of all emissions of this gas that wouldn't need further comments.
Then, there's the combustion of vegetable matters, mainly wood, for the more and more frequent forest fires, caused by man.
Then, also rubbish discharges produce a lot of CO2 for the fermentation and decomposition of organic wet matter and our breeding farms (animals' dung decomposition and their breathing).

The natural sources of CO2, that are the background concentration of this gas without human production, are above all, the oceans and, then, volcanic eruptions and fumarole, swamps (fermentation of organic matter), the decomposition of dead organic matter in the soil and

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