Gas with greenhouse effect
The gas with greenhouse effect ( GES ) are Gaz which contribute by their physical properties to the Greenhouse effect. The increase in their concentration in the Terrestrial atmosphere is at the origin of the Climate warming.
The principal not-artificial gases with greenhouse effect are:
- vapor of Water (H2O),
- the Carbon dioxide (CO2),
- the Methane (CH4),
- the Protoxide of nitrogen (N2O) and
- the Ozone (O3).
The industrial gases with greenhouse effect include fluorinated Gaz like:
- the Chlorofluorocarbon S (CFC) and HCFC -22 like the freon,
- the Perfluorométhane (CF4)
- the Hexafluoride of sulfur (SF6).
The steam is at the origin of 55% of the effect of serre.
Le additional Carbonic gas released by the human activities is responsible for 55% of the increase in greenhouse effect.
The mechanism of the greenhouse effectUnder the effect of the GES, the terrestrial atmosphere behaves as the pane of a greenhouse, letting enter a big part of the solar radiation, but retaining the Rayonnement Infrarouge re-emitted.
The transparency of the atmosphere (in the visible one) makes it possible the solar radiation to reach the ground. Energy thus brought is transformed there into heat. Like any hot body, the surface of the ground tends to radiate part of its heat towards the more cold bodies which surround it. But the GES and the Nuage S are opaque with the infra-red raies emitted by the ground. By absorbing these radiations, they imprison the Chaleur close to the surface of the sphere, where it heats the low atmosphere.
The greenhouse effect, mainly due to the steam (0,3% in volume, 55% of the greenhouse effect) and to the clouds (17% of the greenhouse effect), carries the average temperature on the surface of the ground of -18 to +15°C.
Emissions which had with the human activities
The gas concentrations with greenhouse effect in the atmosphere increase since the 19th century, and with an increasingly strong speed. The phenomenon is mainly due to the human activities, comme :
- the massive use of Combustible S Fossil S: in a few tens of years, one rejected into the atmosphere of the considerable quantities of Carbon dioxide coming from Carbone lengthily accumulated in the basement since the primary era. The increase in the concentration of CO2 in the atmosphere which results from it, is the independent factor of Climate warming. Fossile fuels sont :
- the Deforestation: a mature forest is an important carbon tank. The disappearance of surfaces increasingly larger of forest to the profit of cultures or pastures (storing a less quantity of organic matter), causes to increase the rejections of CO2 in the atmosphere. Indeed, the growth of young trees cannot absorb carbon as much any more that the degradation of the dead trees generates some.
- the use of CFC in the systems of Refrigeration and Air-conditioning (regulated by the Protocol of Montreal) also led to alarming rejections, in particular because of lifespans in the atmosphere particularly long.
- the Protoxide of nitrogen and the Méthane are also taken into account in the international agreements, but not the Ozone. The stratospheric ozone exploits a crucial role of protection against radiation Ultraviolet S. Its impact climate warming is minor compared to his importance as a filter.
- rejections of Natural Methane, natural, and not S: the animals (mainly ruminant and the Termite S), flooded surfaces (Estuary S, Marsh, Rice plantation S) produce natural methane instead of CO2 (thus without added carbon). One can charge to the increase in the livestock of Bovidae as to the discharges, an increase in the methane emissions. However this gas, even if it is degraded rather quickly in CO2, presents a radiative Forçage higher (and thus a Potentiel of total warming increased). Conversely, when produced methane can be developed, it constitutes a clean and renewable fuel.
The Protocole of Kyōto is given like objective to stabilize then to reduce the emissions of GES in order to limit the Climate warming.
The Potential of total warmingEach GES has a different effect on the total warming. For example a methane molecule to an impact on the greenhouse effect 23 times stronger than a molecule of CO2. Then to compare the emissions of each gas, according to their impact on the climate changes one prefers to use a common unit: the CO2 equivalent or the carbon equivalent; rather than to measure the emissions of each gas.
The CO2 equivalent is also called Potentiel of total warming (PRG). It is worth 1 for the carbon dioxide which is used as reference. The potential of total warming of a gas is the factor by which it is necessary to multiply its mass to obtain a mass of CO2 which would produce an equivalent impact on the greenhouse effect. For example, methane has a PRG of 23, which means that it has a capacity of warming 23 times higher than the Carbon dioxide.
For the carbon equivalent, one leaves owing to the fact that one kg of CO2 contains 0,2727 kg of carbon. The emission of one kg CO2 is worth thus 0,2727 kg of carbon equivalent. For other gases, the carbon equivalent is worth:
carbon equivalent = PRG X 0,2727
One can note that the combustion of a ton of carbon corresponds well to the emission of a ton are equivalent carbon of CO2.
This measuring unit is very useful to determine the emissions produced by a company, for example. One can thus carry out a total assessment which takes into account the direct emissions (Combustion S, consumption of energy, Transport S) and indirect (manufacture and transport of the sub-contracted products).
- N.B. the Biosphère accounts for 540 with 610 WP of carbon, ground by retaining 1 500 with 1 600 WP. The Océan S séquesterent 38  of it; 000 with 40 000 WP, the Lithosphere of 66 with 100 Tt (million gigatonnes).
The November 3rd 2006, the World Meteorological Organization (OMM) confirmed that the world concentrations of CO2, far from decreasing, and in spite of the protocol of Kyoto, reached new records in 2005:
- the average content of the atmosphere of CO2 was of 379,1 shares per million (ppm) (0,5% of more than in 2004, and approximately + 2,9% since 1993!).
- the protoxide of nitrogen (N2O) also increased passer by with 319,2 Pb, (0,2% of more than in 2004, and 2,5% of more since 1993!).
In 2007, China should exceed the United States for the gas emissions with greenhouse effect. The emissions of Carbon dioxide should pass from 5,6 billion tons in 2006 to 6,02 this year in this country, which accounts for approximately 22% of the world total.
Duration of stayThe gases with greenhouse effect, once in the atmosphere, are eliminated only gradually. That also means that even if one completely stopped emitting gases with greenhouse effect, the already emitted gases would continue to act during still several centuries. They can be extracted from several manners about it:
- by a natural phenomenon (the Rain and condensation withdraw the steam of the atmosphere);
- by a chemical reaction intervening in the atmosphere (methane, for example, reacts with the radicals Hydroxyle naturally present in the atmosphere to create of CO2);
- by a chemical reaction intervening with the interface between the atmosphere and the surface of the sphere (CO2 is reduced by Photosynthèse by the plants or east dissolves in the Océan S to form ions Bicarbonate and Carbonate (CO2 is chemically stable in the atmosphere);
- by radiations: for example, the electromagnetic radiations emitted by the Sun and the cosmic radiations “break” the molecules in the roadbases of the atmosphere. Part of the Halocarbure S disappear from this manner (they generally chemically inert, therefore stable when are introduced and mixed in the atmosphere).
Except the steam, which is evacuated in a few days, the gases with greenhouse effect take very a long time to be eliminated from the atmosphere. Being given the complexity of the atmospheric system, it is difficult to specify the exact duration of their stay. Here however some estimates of their lasted of stay, i.e. time necessary so that their concentration decreases by half.
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