Everyone knows the prediction that the “greenhouse effect” will modify the climates around the world.

According to the projections made in 1992 by the Intergovernamental Panel on Climate Change (IPCC), they made an analisys and predicted that if no additional stepd are taken to reduce emissions of CO₂ and other problematic gases, then by about the year 2040 the average global air temperature will be 1⁰C higher than the present. By 2100 it will increase by still another 1.5^oC. The total amount of global rainfall increase, although there will be regions that will receive less rainfall than before these changes took place. Annually, The number of days having intense rain showers or very high temperatures both will increase.

Sea levels will rise by about 18 cm by 2040 and by 48 cm by 2100, effects due mainly to the thermal expansion of seawater and the melting of glaciers. Although this increase in the sea level may seem small, there are countries such Bangladesh in which much of the population currently lives on land that would be flooded by a rise in the sea level of only about 50 cm. Temperature and misture changes will occur quickly compared to those that have taken place in the past, and consequently some ecosystems will be destabilized.

The temperature increase will probably be greater close to the Polar Regions. There may well be enough melting of ice in the artic region for the Northwest Passage to be used for commercial transport. In subtropical areas, the monsoon rains will likely be heavier. Also will be probably will have more extreme heat waves in summer and fewer prolonged cold snaps in winters. There will be longer frost-free growing seasons at northern latitudes, but increased changes that heat stress will affect cr ops grown there.

The phenomenon of global warming is generally considered to be our most crucial worldwide environmental problem. Unlike stratospheric ozone depletion, which has manifested itself in spectacular fashion in the form of the ozone hole.

THE MECHANISM OF THE GREENHOUSE EFFECT

The earth’s surface and atmosphere are kept warm primarily by energy from the sun.

The phenomenon that worries environmental scientists is that increasing the concentration of the trace gases in air that absorb thermal infrared light would results in the redirection of even more of the outgoing thermal infrared energy and would thereby increase the average surface temperature beyond 15⁰C. This phenomenon will be referred to as the enhanced greenhouse effect, to distinguish its effects from the one that has been operating naturally for millennia.

In the next picture we can observe a schema of the operation of the greenhouse effect in the earth’s troposphere .

THE MAJOR GREENHOUSE GASES

• CARBON DIOXIDE:

The carbon dioxide molecules currently present in air collectively absorb about half of the outgoing thermal infrared light having wavelengths in the 14-16 µm regions, which a sizeable portion of that in the 12-14 and 16-18 µm regions, which are called shoulders of the main 15 µm absorption 

In table above we can see the infrared absorption for carbon dioxide.

In the table above we can see the 19 top carbon dioxide producers and the percentage that each one produce.

• WATER VAPOR

Water molecules, always abundant I air, absorb thermal IR light due to the H-O-H bending vibration, the peak in the spectrum for this absorption occurs at about 6.3 µm. Thus almost all the relatively small amount of outgoing IR in the 5.5-7.5 µm regions is intercepted by water vapor. There are other water vibrations the remove thermal infrared light of wavelength 12 µm and longer. In fact the water is the most important greenhouse gas in the earth’s atmosphere, though on a per molecule basis it is a less efficient absorber than is CO₂.

The equilibrium vapor pressure of liquid water, and consequently the maximum concentration of water vapor in air, increases exponentially with temperature. Thus the amount of thermal IR redirected by water vapor will rise as a result of any global warming induced by the other greenhouse gases and will amplify the temperature increase. Since it comes about as an indirect effect of increasing the levels of other gases. Consequently, water is not usually listed explicity among gases whose increasing concentrations are enhancing the greenhouse effect.  Water in the liquid form droplets in clouds also absorbs thermal IR.

In this table, we can observe the infrared absorption spectrum for molecules of water in the vapor state. The largest amount of absorption in the thermal IR occurs at and around 6.3 µm. 

In this table we can compare the infrared absorption for carbon dioxide and water vapor.

OTHER SUBSTANCES THAT AFFECT GLOBAL WARMING

  The injection into the atmosphere even in trace amounts of gases that can absorb thermal IR light will lead to additional global warming, that is, the enhanced greenhouse effect. Particularly serious are pollutant gases that absorb thermal IR in the window region, since the absorption by H₂O and CO₂ in other regions is already so great that there remains little such light for trace gases to absorb. In considering which potential pollutants might contribute to global warming.

Now we can observe in the following tables, a short summary of information about the greenhouse gases, in which we can find the current abundance, the rate of increase, and the relative warming effectiveness of the different kinds of gases that we can find in the atmosphere.

• TRACE GASES: ATMOSPHERIC RESIDENCE TIME

IN order to assess the impact of any substance upon the enhanced greenhouse effect, it is necessary to know long the substance can be expected to remain in the atmosphere, since the longer its atmospheric lifetime, the greater its total effect. Every atmospheric gas that is present in or near steady state can be characterized by a residence time T_avg , which represents the average amount of time one of its molecules exists in air before it is removed by one means or another.

The average residence time of the greenhouse gases carbon dioxide, nitrous oxide, and the CFCs

Is more than a century, so the influence of these gases that we are emitting now into the atmosphere will extend over very long periods of time, in contrast the methane only has a residence time of a decade.

• METHANE:

Nowadays is estimated that methane has produced about one-third as much global warming as carbon dioxide.

There are six different sources of atmospheric methane: in order of importance they are wetlands, fossil fuels, landfills, rumiants animals, rice paddies, and biomass burning.

• NITROUS OXIDE

The greater part of the natural supply of the gas comes from release by the oceans and processes occurring in the soils of tropical regions contribute most of the remainder. The gas is a byproduct of the biological denitrification process in aerobic environments and in the biological nitrification process in anaerobic environments. In denitrification fully oxidized nitrogen in the form of the nitrate ion, NO₃^- is reduced mostly to molecular nitrogen, N₂. In nitrification, reduced nitrogen in the form of ammonia or the ammonium ion is oxidized mostly to nitrite (NO₂^-) and nitrate ions.

• CFCs

The CFCs are a gaseous compounds that contains molecules with carbon atoms bonded exclusively to fluorine or chlorine have perhaps the greatest potential among trace gases to induce global warming, since they are both very persistent and absorb strongly in the 8-13 µm window region. The chlorofluorocarbons CFCl₃ and CF₂Cl₂ have already been released into the atmosphere in large quantities and have long residence times. Due to this persistence, and to their high efficiency in absorbing thermal IR in the window region, each CFCs molecule has the potential to cause the same amount of global warming as do tens thousands of CO₂ molecules.

THE TEMPERATURE CHANGES:

  The combined greenhouse effect enhancement from the increases in concentration of the trace gases methane, nitrous oxide, ozone and the CFCs is now almost as large as that from the increases in carbon dioxide. In order to conveniently summarize the temperature- enhancing effects of all greenhouse effects gases by a single number, the concept of an Effective Carbon Dioxide concentration has been divised.

  An increase in the average atmospheric temperature means that more energy is contained in the air and water at the earth’s surface, and that more violent weather disturbances could result.

  Ironically, an increase in greenhouse gases is predicted to cause a cooling of the stratosphere. This phenomenon occurs for two reasons, in the first place, most thermal IR is absorbed at low altitudes, and little is left over to warm the stratosphere. Secondly, at stratospheric temperatures CO₂ emits more thermal IR to space than it absorbs, and so increasing its concentration cools the stratosphere.

All these changes in the stratosphere could cause an impact over the human health, the scientist have predicted that the human will be affected by the greenhouse effect, for example, the expected doubling in the annual number of very hot days in temperature zones will affect people who are especially vulnerable to extreme heat, such as the very young, or the very old, and those having chronic respiratory diseases, heart disease, or high blood pressure.

The increase of the temperature could be ralationed with the increase of the domestic violence and civil disturbances.

Now we are going to describe the main consequences of the greenhouse effect:

• Health consequences:

The increase of the temperatures will cause an increase in death and illness, especially among the urban and yhe urban poor people, with li mited access to the air aconditioning.

  A recent study of many of diffrents regions in Europe showed that the populations have adjusted successfully to mean summer temperatures renging from 13.5^oC and 24.1^oC, and while heat-releated mortallity started around 17.3^oC in the north Findland, it first set in at 22.3^oC in London, and 25.7^oC in Athens.

  AT the same time, all populations showed much greater deaths in winter time, and thus even a small decrease in winter deaths would greatly outweigh a small heat death increase.

  With a temperature increase diseases as the Malaria, can appear again, it is due to because the mosquitoes that transmit the malaria ordinarialy need winter temperatures between 16-18^oC.

In this table table we can observe the temperature variations from the year 1850 to 2000.

Are there other causes for the global warming effect?

The global warming could be caused for other circumstances, now we know that for a long time that there is a correlation between solar activity and temperature. Probably, solar brightness has increased about 0.4 percent over the past 200-300 years, causing an increase of about 0.4^oC, and the trend over tha last decades is equivalent to another 0.4^oC to 2100. A recent AOCGM study showed that the increase in direct solar irradiation over the past 30 years is responsible for about 40 percent of the observed global warming.

Other possible reason that can have influence, are the clouds, today about 65 percent of the earth is covered with clouds, an extremely significant factor when determining the warming effect of the CO₂. This is because the clouds help to keep the Earth cool by refelcting the sun’s rays, while at the same time warming it by keeping in the heat the overall effect for low –level clouds is a cooling of the earth, so that more low-level clouds mean lower temperatures.

Svensmark, along with several others, has shown that there seems to be a clear conection between global low-level cloud cover and incoming cosmic radiations. The explanation for it is probably that the cosmic rays produce ions, which together with small particles in the atmosphere can create the basis for the development of low-level clouds. And more cosmic radiation is the result of lower solar activity, which in turn correlates with longer sunport cucle duration.

This theory also has the tremendous advantage, compared to the greenhouse theory, that it can explain the temperature cahnges from 1860 to 1950, which the rest of the climate scientist with a shrug of the shoulder have accredited a natural variation.

In the next table we can observe the entire factors that have inffluence in the atmosphere warmning.

In the table we can observe the incoming extra energy to the earth due to changes in the past 250 years.