Global Warming and Green House Effect

The world is facing ecological problems like environmental pollution, increase in population, deforestation, energy crisis, and soil erosion and so on. An outcome of the atmospheric pollution is warming of the earth’s environment. Warming of the earth atmosphere is a serious problem and in twenty-first century this may be a problem of global concern. There is a clear indication that the temperature of the earth has increased slightly during the past 50 years. It is clear from the temperature records of the last 50 years illustrated in the following Fig. 14.1.

This increase in temperature of atmosphere is very dangerous for living organisms.

Though there are numerous causes for the global warming, the following two factors are considered to be very significant:

1. Industrialization

2. Deforestation

During the last two decades there has been tremendous growth of industries in the world. These industries release toxic gases, chemicals and effluents in huge quantities into the environment .The industrial wastes produce many harmful effects and ultimately disturb the ecosystems. The toxic gases and effluents released into the environment cause pollution of air, water and soil.

Deforestation is mainly due to increase in population, industrialization, urbanization and increasing agricultural activities. Deforestation has led to soil erosion, wasteland development and extinction of certain species from the flora and fauna. Deforestation is taking place at an alarming rate. For healthy environment one-third area of the earth should be covered by the forest but the total forest cover in India is much less than 33 per cent.

Data provided by the Remote sensing Technology reveal that only 17 per cent area of India is covered by the forest. After 1950, about 4.2 million hectares of forest were destroyed and since 1980 every year about 1.5 million hectare forest area is either converted into agricultural land or used for some other purposes.

Due to two aforesaid reasons the concentrations of CO₂ gas is increasing in atmosphere. Carbon dioxide at normal concentration (0.03%) is not considered as a pollutant but its concentration above 0.03% in the atmosphere has an adverse impact on our climate and living organisms. Besides CO₂, some other gases present in our atmosphere are also responsible for raising the temperature of the earth and its environment.

Green House Effect:

It is a universal truth that the sun is the main source of energy on the earth. The sun is continuously radiating energy in the form of electromagnetic waves into the space. It has been calculated that one part out of two billion parts of total solar energy radiated from the sun reaches the earth because of small size of the earth and very long distance from the sun.

The solar energy reaches to the earth atmosphere in three forms:

(i) Ultra-violet radiation

(ii) Visible light (VIBGYOR spectrum)

(ii) Infra-red and radio waves

Cosmic radiations do not reach to the atmosphere of earth. When the solar radiations first fall on the top of atmosphere the harmful ultraviolet radiations are absorbed by the ozone layer in the stratosphere and are prevented from reaching the earth surface. Thus ozone layer acts as a protective layer in the stratosphere. The visible light and infra-red rays then pass through the carbon dioxide layer in the lower region of the atmosphere (troposphere) and ultimately fall on the earth surface.

Since infra-red radiation has heating effect, it warms up the earth, its atmosphere and various objects. A part of infra-red rays falling on the earth surface is reflected back into the outer space. Infra-red radiation coming to earth from the sun are of short wavelength but the infra-red rays reflected from the earth and its various objects are of long wave lengths.

The infra-red radiation reflected from the earth cannot escape out from the carbon dioxide layer present in the atmosphere. CO₂ and some other gases like methane, nitrogen oxides and chlorofluorocarbons (CFCs) act as the glass panels of a green house or window panes of a car which allow the solar radiations to pass through and heat the surface of earth but do not allow the heat radiated from earth is surface to pass through thereby trapping it in the process.

These gases have the ability to absorb infra-red radiation reflected from the earth surface. Therefore the blanket of these gases in the atmosphere traps all the infrared rays which produce heat on the earth surface. The heating of earth’s atmosphere due to trapped infrared rays reflected from the earth surface is called Green House Effect which causes global warming.

The rise in temperature of earth’s atmosphere caused due to green house effect depends on the amount of carbon dioxide present in the atmosphere. At normal CO₂ concentration (0 03%) in the atmosphere the surface temperature of the earth remains constant due to energy balance of the sun rays which strike on the earth, heat it and then radiate back into the space.

This is called Energy Budget. But when there is increase in CO₂ concentration in the atmosphere, the thick layer of CO₂ prevents the heat from being radiated out into space. This layer of CO₂ thus functions as a glass panel of green house or glass window of a motor car which allows the sunlight to filter through it but prevents heat from being radiated back into the outer space. Thus most of the heat energy absorbed by CO₂ layer of the atmosphere warms up the air in the troposphere. The gases responsible for raising the temperature of the earth and its atmosphere are referred to as green house gases. The different green house gases and their percent ratios are as follows (Fig. 14.3).

1. Carbon dioxide — 55 %

2. Methane — 15%

3. Chlorofluorocarbons (CFCs) — 24 %

4. Nitrogen oxides (N₂O and NO) — 6 %

Sources Discharging Green House Gases:

The various sources responsible for discharge of green house gases into the earth’s atmosphere and their contribution (in percent) are presented in the Tables 14.1 and 14.2.

Table 14.2. Sources of green house gases:

Carbon dioxide gas plays the following important roles in the environment:

1. It produces green house effect causing heating of the earth and its atmosphere. (Table 14.3).

2. Carbon dioxide is a raw material for photosynthesis in green plants.

3. The gas dissolved in water reacts with lime to form carbonate rock.

Carbon dioxide gas is confined only to lower level of atmosphere (troposphere).

The main sources through which the CO₂ is released into the atmosphere are as follows:

(i) Burning of fossil fuels

(ii) Decay of dead organisms

(iii) Respiration of living organisms

(iv) Automobile exhausts

(v) Thermal power plants

(vi) Cultivation of land

(vii) Eruption of volcanoes

(viii) Domestic cooking

(ix) Forest fires.

Carbon dioxide present in the earth’s atmosphere not only checks infra-red radiations from being reflected back into the space but also produces heat effects. The average temperature of the earth remains almost constant because of the balance between the amount of solar energy reaching the earth surface and the amount reflected back into the outer space from the earth surface. Sometimes, this balance is disturbed.

CO₂ is emitted into the atmosphere is equivalent of more than 6,000 tonnes of carbon per year. About 194 Gt. (1 giga tonne = 1000 million tonnes) CO₂ is produced by biosphere annually. 6 Gt CO₂ is released from burning fossil fuels and rest comes from burning forests and about 16-9 Gt carbon is added to atmosphere through human activities. Small amount of CO2 is released into atmosphere by volcanoes. About 1.7 ppm (parts per million by volume) of CO₂ is added to environment every year.

A part of atmospheric CO₂ is consumed in photosynthesis and respiration and decomposition release it again into the atmosphere. In the recent past the average volume of CO₂ in the atmosphere has increased from 316.8 ppm (part per million) in 1960 to 366.7 ppm in 2000 (Table 14.3) and in the beginning of 21st century it may reach to about 400 ppm. According to an estimate, by the year 2040 the concentration of CO₂ may reach up to to 500 ppm. There is an indication that if CO₂ concentration becomes double, the average temperature of earth will rise by 2°C.

In addition to CO₂, some other gases like nitrogen oxides (N₂O) and (NO), methane (CH) carbon tetrachloride, (CCI₄), Chlorofluorocarbons (CFCs) are also responsible for increasing the temperature of the earth and its atmosphere.

It has been observed that carbon dioxide alone increases the temperature by 50 per cent, CFCs by 20 per cent and other air pollutants by 10 per cent. More recently, the role of methane in atmospheric temperature changes received much attention. Methane has a global warming potential about 25 times more than CO₂ and accounts for about 15 per cent of the global warming (Brown, 1994).

Annual global emission of methane in 1997 was estimated to be 7.1 tonnes from land fill sites. According to an estimate, the total concentration of CH₄ was 1630 parts per billion (ppb) in 1984. The main sources of methane are sheep and cattle dung, wet lands, biomass burning mining of coal and mineral oils paddy fields and bacterial biomass. Roots of paddy plants absorb methane from muddy soil and translocate that along with solutes to aerial parts through vascular tissues from where it is released in the atmosphere.

Impacts of Global warming:

Global increase in temperature of earth will have serious consequences on human society, agriculture, plants and animals.

These are discussed below:

1. Sea-level rise Global warming is likely to result in a rise in sea-levels that could threaten many coastal areas around the world. It will also melt much glacier, especially around Greenland. Sea-level changes will complicate life in many coastal regions. A 100 cm rise could submerge 6 per cent of the Netherlands, 17.5 per cent of Bangladesh and many islands will have to spend huge amounts of money to protect their shorelines while poor countries may be forced to evacuate low-lying coastal regions. New marshes will also form in many places.

2. Increase in the flow of rivers and change in rainfall pattern.

3. Occurrence of more cyclones and hurricanes.

4. Fresh water will be contaminated with the salty water of sea.

5. Human health. As a result of global warming human populations will be displaced. In a warmer climate people will get more frequently sick. Diseases now found in the warm tropical areas will spread to new regions. Many diseases are transmitted by mosquitoes and other animals when these animals will move into colder regions. Other tropical diseases including dengue fever, yellow fever and encephalitis may spread into new regions. It is also predicted that there will be rising incidence of allergies and respiratory diseases, as warmer air is more charged with pollutants, fungal spores and pollens.

6. Effect on agriculture it has been speculated that due to global warming the world food production might not be seriously affected. However, since people are now adapted to Lain climatic conditions, a drastic change would adversely affect them. The main reason for this would be the shifting of agricultural zones. For example, Southern Canada may benefit from more rainfall and a longer growing season. At the same time the semiarid tropical farmlands, in some parts of Africa, may become further impoverished more insects and plant diseases may also afflict crops and woodlands.

7. The forest vegetation will not be able to adapt with the changing temperature and may face destruction.

8. As a result of global warming, the temperature of southern Europe and Central America will rise and affect the rainfall in these areas.

9. The effect of global warming on the Tropics and Southern hemisphere will be uncertain.

The reaction of a common man on increase of earth’s average temperature will be that it would make no difference if the average temperature of the earth increases by 1.2°C. But, in fact, it is not so. No matter, we do not experience the impact of this gradual increase in the average temperature of the earth but the various conclusions drawn by the scientists on the basis of their researches are eye opener and alarming. Tata Energy Research Institute, New Delhi in its report (TERI 2000-2001) has pointed out the various probable losses to be caused by the increase of earth’s average temperature in the world by 2.5 °C (Table 14.4).

The Meteorological Department has conducted several experiments and has estimated marked changes in the climate during the present century. The experiments have predicted that in future global average temperature will rise by 1.4°C to 5.8°C. This will exert a great impact over the land, coastal areas and at high altitudes. The weather frequency appears to be disturbed as more floods, droughts, storms and cyclones are occurring.

Ozone Depletion and Ozone Hole:

Ozone gas is found on the upper surface of stratosphere at the height of about 50 km in the form of a layer called ozonosphere.

The main functions of ozone layer are as follows:

1. It regulates the weather and climate of the earth.

2. It filters away the ultraviolet radiation and protects the earth from harmful effects of UV rays. Thus it acts as a protective layer.

Earth receives ultraviolet radiation in three forms:

(i) UV-A in the wavelength range of 315-400 NM

(ii) UV-B with wavelength from 289-315 NM and

(iii) UV-c with wavelength from 100-280 NM

Out of these, UV-B in the wavelength range from 250-315 NM is most dangerous. It affects the living organisms in many ways. Sunburn, ageing, wrinkling of skin, cataract of eye, destruction of protein, mutation of genes leading to skin cancer or melanoma, etc. are some of the common effects of UV radiation on human population. Ozone is an unstable gas and for its formation and destruction both UV rays are essential which come from the sun.

The following reactions are involved:

This is continuous process. Thus ozone is in dynamic equilibrium. In the processes of forming and breakdown of the ozone molecule a part of the harmful ultraviolet rays is converted into infra- red rays which is not lethal to man. In addition, ozone prevents the escape of UV-rays into the earth’s atmosphere. Thus a balanced chemical reaction is set in. The retarded rate of formation and increase in destruction of ozone molecules allow UV-rays to escape into the atmosphere.

This leads to less ozone formation which is commonly known as ozone depletion. The man made nontoxic, inflammable and highly stable chemicals Chlorofluorocarbons (CFCs; CCI₃F and (CI₂F₂) as well as CCl₄, CH₄ etc. are main chemicals which check the ozone formation (table 14. 5)’The main damaging among them are CFCs.

Since their discovery in 1928, CFCs have been used as cooling materials in refrigerators and air conditioners, propel aerosal sprays, to clear computer chips and to make foam rubber and polystyrene containers. The British chemist James Loverlock developed a device to detect CFCs in late 1969s and reported that CFCs were a great problem in the environment. He found that CFCs once released in to the atmosphere remain intact and they go on spreading indefinitely mixing with other molecules in air until they are dispersed over the globe.

Two US chemists, Rowland and Molina reported in 1974 that USA alone was producing 380 million kg of CFCs and when released in atmosphere they remain intact for 50 to 100 years and slowly drift towards stratosphere 12-50 km above the surface of the earth. These carbon compounds of the stratosphere in presence of ultraviolet rays coming from the sun break and produce chlorine in nascent state which breaks the ozone molecules and reduces ozone content of the atmosphere. One atom of chlorine is sufficient to destroy a lac of ozone molecules and since this process is cyclic, the damage being caused is tremendous.

The reaction is given below:

(i) Cl + O₃ → ClO (chlorine monoxide) + O₂

ClO → Cl + O

Chlorine atom liberated at the end of reaction breaks another ozone molecule in cyclic chain:

Ozone hole:

Ozone hole means complete disappearance of ozone layer over a part of the atmosphere (Fig. 14.5). Ozone hole is formed by intense UV activity on CFCs. It was first detected in 1975 but its worst effect was noticed in 1985 by some British scientists. They saw ozone hole over Antarctica. Later on, the presence of ozone hole was confirmed over the North Pole also. It starts appearing at the end of winter, shows maximum display in spring and disappears in summer.

This is because in winter the air is heavy and industrial gases like CFCs get concentrated over an area in Antarctica where the maximum damage of ozone layer has been noticed. In Antarctica CFCs bearing winds become frozen to form ice crystals in winter. During spring when ice melts the trapped CFCs and CIO are freed at once which, in turn, release nascent chlorine to attack ozone. The overall sequence of reactions is illustrated in Fig. 14 4. Consequently, the hole becomes large during the spring.

Global Concern:

Global warming is the Global concern. In this context, the representatives of many countries assembled and held a conference at Montreal in 1987 called Montreal Protocol. It was decided in the conference to limit the use of CFCs and cut level of CFCs production to 50 per cent by 1999. But India and China opposed and refused to sign this protocol and this was supported by many developing countries on the ground that their per capita consumption of CFCs was only 1/100th as compared to developed and industrialized countries.

Later on, in London Protocol (1990) India, China and several other countries demanded more time to reduce CFCs consumption. The developed countries agreed to stop CFCs consumption completely by 2000 and for developing nations the time limit was extended to 2010. Developed countries have also agreed to establish a multilateral fund under Montreal Protocol to provide financial support to developing countries for that purpose.

In recent years, few substitute of CFCs have been explored. Two viable substances in the form of HCFC and HFC-34 are considered to be harmless for ozone. Out of these two, HFC-34 is less harmful because of absence of chlorine in it, although it is expensive, inflammable and toxic in nature. There are some other substitutes such as, Butane and Propane which are less expensive, less harmful and freely available. The ozone depletion and its impact was discussed in detail in London agreement at global level. In 1988, the world conference on the changing atmosphere was held in Toronto (Canada).

There it was decided to reduce 20% carbon dioxide emissions by the year 2005. Then in 1990 the second world conference on climate was held in Geneva. In 1992, the Earth Summit was held in Rio de Janeiro but with no concrete results because of interference of the industrialized countries. The United States and Japan have not been able to decide so far to reduce CO₂ emissions although they verbally declare their commitment to the Toronto agreement every now and then. The European countries, however, have set the goal of stabilizing CO₂ emissions at the level of 1990 by the year 2000.

At present on the basis of Montreal Protocol India has established a ozone cell under the Ministry of forests and Environment with the help of UNDP (United Nations Development Programme). The ozone cell has prepared a document under National Programme for phasing out of ozone depleting substances (ODS). This document has recommended two billion dollars for India to phase out “ODS” completely.

This includes the cost of new technologies and expenses for creating public awareness and coordinating the activities at National level. During the 6th meeting of Executive Committee of the Multilateral Fund held in Nairobi in October 1994, the committee decided to create a fund of 4 million dollars as a contingency grant for India to undertake the programme and extension of technical assistance necessary for the purpose. On this ground, India has developed “R-22” and “R-134” as CFCs substitutes which are presently at trial stage.

Check On Global Warming:

Global warming can be checked by reducing the concentration of CO₂, methane, nitrogen oxides and CFCs in the atmosphere by adopting the following measures:

1. Plantation of trees at large scale.

2. Increasing the diffusing capacity of oceans for CO₂.

In the photosynthetic process green plants use CO₂ to prepare their food material and release O₂ as a by-product. Therefore, planting trees on waste land and replanting of new trees in place of destroyed trees are most important. If one-third part of the world is covered by the forest then CO₂ will be stabilized. Thus green plants cause decrease of CO₂ concentration through photosynthesis.

Ocean plays a significant role in reduction of CO₂. Carbon dioxide is continuously dissolving in the oceans which is stabilized in the form of carbonate rocks at the bottom of sea. According to an estimation half of the CO₂ evolved is absorbed by the seas and their phytoplankton (free- floating plants).

There is a new method to reduce the CO₂ concentration in environment. According to J.H. Martin the growth of phytoplankton can be enhanced by spraying iron supplement in the ocean. Phytoplankton takes CO₂ from sea water in greater amount due to which CO₂ will decrease in the oceans. Therefore, more CO₂ will dissolve in the oceans resulting in the decrease of CO₂ concentration in the atmosphere. In 1955, 454 kg ferrous sulphate was sprayed in 1600 square km area of Pacific Ocean. After few days there was plenty of growth of phytoplankton in sea water of that area and due to that the colour of water became green in place of blue. About 6-21 per cent CO₂ can be reduced by this method.

United Nations Conference on Environment and Development (UNCED) or Earth Summit at Rio de Janeiro was held from 3-14 June, 1992 in which more than hundred countries participated. In Earth Summit, Global Warming was one of the important topics. In the Earth Summit, USA and other developed countries including EEC signed convention on climate change, but they refused to make a specific time bound commitments to bring down the levels of emission of carbon dioxide and other greenhouse gases.

The Second Earth Summit was organised in 2002 by UNCED in Johannesburg (South Africa) in which 110 countries participated. The main theme of the summit was sustainable development. In the protocol of the summit it was reiterated that the activities responsible for global warming should be checked and the use of CFCs should be completely banned by the end of 2010.

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