Earth as the absorber and the emitter of radiation
The surface of earth turns into a radiator of energy in the infrared radiation due to its heating by the virtue of sun light. The radiation is directed to go back into the space where it is interesting to reveal that very small portion of it manages to go back. A large number of emitted back infrared radiations is absorbed by the green house gases.
The long wave energy absorbed by the atoms of the green house gases adds into the atmosphere additional energy. The radiation absorbed by the atoms is re-emitted into all directions. About 90 per cent of this energy is emitted towards the earth’s surface where it is once again absorbed. The heating of the surface once again results in the radiation which is again absorbed by the atoms of green house gases that are spread in the blanket of atmosphere and the cycle goes on until or unless no long wave radiation is available.
Green house gases playing with the global temperature
The temperature of earth can be managed by controlling the amount of heat added to the atmosphere due to the green house gases. It is possible by controlling the amount or quantity of green house gases especially carbon dioxide (CO2) in the atmosphere of earth. Since 1700, the green house gases are only increasing in the atmosphere due to industrial revolution. Scientists are only able to predict the upcoming warmth due to the ever increasing amount of green house gases. The prediction is made possible by the help of computer modeling. It has been shown by the models that the doubling of concentration of main green house gas carbon dioxide will increase the temperature by 1 to 3 degree Celsius. A number of negative feedbacks of increasing cloud cover are not accurately stimulated by the numeric equation of computer models. Increased radiation will swiftly evaporate the oceans and as a result vapors will make the clouds thicker. These clouds will the serve the purpose of emitting back the solar radiation into the space so less energy is absorbed by the atmosphere and the surface of earth. Less solar energy absorbed by the surface will affect the green house effect, and decrease it.
- Carbon Dioxide
In 2005, the average concentration of the carbon dioxide in the atmosphere was 380 parts per million. The concentration was about 280 parts per million before the 1700 A.D. the increase in the level is mainly due to the role of human beings. After 1700, the industrial revolution began that emitted extensive amount of carbon dioxide and largely affected the atmosphere. Main source of carbon dioxide is the fossil fuels that were burnt to run the industry. Besides, transportation, electricity generators, space heating, vegetation changes and cooking are also important in changing the concentration of green house gases especially carbon dioxide. About 65 per cent of extra carbon dioxide found in the atmosphere is emitted from the fossil fuels. The deforestation and the conversion of forests and woodlands to agricultural fields is responsible for 35 per cent of the increased amount of carbon dioxide in the atmosphere. 20 to 100 times more carbon dioxide per unit can be hold by natural ecosystems than the agricultural systems.
The strongest green house gas per molecule is artificially created chlorofluorocarbons. Their overall impact in the green house effect is less due to their low concentration in the atmosphere. Latest statistics have revealed that the concentration of such molecules will start to decline in coming future as to less emission. It is earlier reported that holes in ozone were created over the North and South Poles. In last two decades, this information played vital part in increasing awareness and many nations cutback the use of these chemicals and a general decline in global stratospheric ozone levels. The Montreal Protocol agreement was signed in 1987 by 46 nations in which an immediate timetable was proposed to reduce the production of chlorofluorocarbons and their usage.
The concentration of methane gas has increased by 150 per cent since 1750. The cultivation of rice, the domestically grazing animals, landfills, termites, coal mining, and gas and oil extraction are the primary sources that have enlarged the quantity of methane in atmosphere.
The rice paddy flooding is associated with the anaerobic conditions that finally results in the creation of methane gas. Scientists consider that the rice paddies make extensive contribution as the production is more than double since 1950s. The herbaceous digestion in grazing animals results in methane release. Such addition in the quantity of methane is quadrupled in last century as per the researchers.
- Nitrous Oxide
It is estimated that the average increase in the amount of nitrous oxide per year is about 0.2 to 0.3 per cent. The sources of nitrous oxide are land-use conversion, biomass burning, fossil fuel combustion and soil fertilization.
The largest amount of nitrous oxide is emitted during the process of deforestation and the transformation of savanna, grassland and forest ecosystems in to fields for agriculture. The decomposition of vegetation and soil also release nitrous oxide due to decomposition. The use of fertilizers that contain nitrate and ammonium fertilizers to improve the growth of plant also produce nitrous oxide.
The role played by the ozone in green house effect is still undetermined. The levels of this gas in the atmosphere for the past 25 years are not authentically available. In two parts of the atmosphere, the concentrations of ozone are not available. At the altitude of 15 to 55 kilometers above the surface the major part of ozone (about 97 per cent) is present in the stratosphere. The increase in chlorofluorocarbons in past years has reduced the thickness of ozone in stratosphere. After 1970s the researches have revealed about 70 per cent of the total column ozone amount on Antarctica has been decreased. As a result of photochemical smog ozone is artificially created.
The green house effect has enabled the atmosphere to trap and than to remit the radiation propagated from the sun. About 90 per cent of the long wave energy that is emitted back to space is intercepted and absorbed by the green house gases. With the increase in the amount of green house gases, the green house effect has started to offer some troubles. Experts claim that since the beginning of this century the average temperature of our globe has been already increased by 0.3 to 0.6 degree Celsius. It is forecasted that the temperature will rise about 1 to 3 degree Celsius by the middle of this century.