Global Climatic Change


For the last billion years or so, earth’s atmosphere and hydrosphere have been composed of approximately the same balance of chemical components we live with today. The earth has a unique mechanisms for stabilizing and controlling the global climate. These mechanisms are as follows –

  • (i) The plants and animals balance carbon dioxide level of the atmosphere which in twin acts as global thermostat. It means these elements control the temperature balance within optimum limits.
  • (ii) The water bodies play important role in regulating global climate.

In recent years, the rapid growth of human population, the rate at which we consume the earth’s resources, extravagant life styles etc. lead to substantial increase in the carbon level of atmosphere which has accelerated the process of climatic change. Factors playing role in climate change are –

  • Green House Effects and Global Warming
  • Ozone Layer Depletion
  • Acid Rain

Green House Effects and Global Warming

Global warming refers to a gradual rise of atmospheric temperature and consequent changes in the radiation balance mainly due to human action leading to climatic change at different levels – local, regional and global.

As per recent estimates, it has been found that the surface air temperature over the past 100 years has increased by about 0.50C to 0.70C.

Why it is happening? – This is due to green house effect.

Working of a Green House

In cold countries, a green house is meant for plants, where total heat, especially during winter season, is not sufficient to support plant growth.

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The transparent walls and roof of the green house are such that these allow the visible sunlight to enter but prevent the long-wave radiations to go out. Thus, the sunlight is absorbed by the soil and structure of the green house. It is then re-emitted as heat which can not pass through the glass. The amount of energy in the green house thus increases until its temperature is high enough for the slight leakage of heat through the glass to take away as much energy as gets in as sunlight.

Subsequently walls and roof re-emit absorbed radiation into the house. Thus, during the day time, infra-red radiation pass into the green house and warm the atmosphere and the ground on which the green house stands. Coating of glass with a non-heat radiation film transparent to sunlight further maximizes heating effect of the radiation.

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Therefore, if our earth has become a green house, then there are certain gases which act like the glass panels of a green house allowing the sun’s rays to pass through but preventing the heat from escaping into the outer space and there by warming the atmosphere.

This is happening due to deforestation and industrialization.

These gases are carbon dioxide (CO2), methane (CH4) nitrous oxides (NOx) and chlorofluorocarbon (CFC) and hence known as green house gases.

Out of these four gases, carbon dioxide contributes about 55%, chlorofluorocarbon contributes about 24%, methane (about 15%) and nitrous oxide (about 6%) towards heating of the atmosphere.

What is the sources of these gases?

  • Burning of fossil fuels and fire woods, large fleet of auto-mobiles and number of factories emit carbon dioxides.
  • Growing paddies, livestock, waste dumps and coal mining are the major source of methane.
  • The use of aerosols as coolants in refrigerators and air conditioning devices release chlorofluorocarbons into the atmosphere.
  • Nitrous oxide is mainly emitted from chemical industries, and due to deforestation and certain agricultural practices.

Construction of green houses in temperate region helps the plant protection and ecological balances whereas concentration of green house gases on the earth’s
atmosphere upsets the earth’s biological system.

Consequences of green house effect

  1. It is estimated that if the present rate of increase in CO2 level continues, it will result in rise of atmospheric temperature by 2°C to 3°C by end of 21st century.
    • This will result in receding many glaciers; melting of icecaps in the polar regions and disappearance of deposits of ice on the other parts of world in large scale.
    • According to an estimate, if all the ice on the earth would melt, about 60M of water would be added to surface of all oceans and low lying coastal areas.
    • A rise in sea-level of only 50-100 cm caused by global warming would flood low lying areas of the world such as Bangladesh, West Bengal as well as densely populated coastal cities from Shanghai to San-Fancisco.
  2. Because of increased concentration of CO2 and due to much warmer tropical oceans, there may occur more cyclones and hurricanes. Early snow melt in mountains will cause more floods during monsoon. According to United Nations Environment Programme (UNEP), within about three decades, rising levels of seas will be able to and flood coastal cities like Bombay, Boston, Chittgang and Manila.
  3. A slight increase in global temperature can adversely affect the world food production. Thus the wheat production zones in the northern latitudes will be shifted to north of temperate latitudes.
  4. The biological productivity of the ocean would also decrease due to warming of the surface layer, which in turn reduces the transport of nutrients from deeper layers to the surface by vertical circulation.

Control and Remedial Measures of Green House Effect

The following measures may be adopted to reduce the ever increasing green house effect –

  1. CO2 concentration can be reduced by drastic cut in the consumption of fossil fuels in the highly developed and industrialized countries like USA and Japan and developing country like China and India.
  2. Scientific efforts should be made to develop alternative efficient fuels. Methane may be a substitute of petroleum. Development of hydro-electric and thermal power are better alternatives.
  3. There should be a restriction on the emission of dangerous CO2, CFCs, and as NO2 from the factories and auto-mobiles.
  4. Limiting the driving days in megacities can be another option. Cities like Singapore and Mexico are following the practice.
  5. In tropical and sub-tropical countries, the solar energy may be developed as an alternative to the fossil fuels.
  6. Biogas plants should be used which is another source of conventional energy for domestic use.
  7. Enhancing afforestation will certainly reduce the CO2 level thereby decreasing the green house effect.

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Ozone Layer Depletion

Ozone is a form of oxygen that has three atoms (O3) rather than the more common two atoms (O2).

  • It is created in the upper atmosphere by the action of solar radiation on oxygen molecules.
  • As far as its position is concerned, it is found in the form of a thin layer in the stratosphere between 15 to 48 kilometre.
  • About 90% of all atmospheric ozone is found in this layer.
  • Oz0ne constitutes only less than 0.002 percent of the volume of the atmosphere.

However, it’s role is very critical as far as lives on the earth is concerned.

  • It strongly absorbs ultraviolet radiation from the sun.
    • Ultraviolet radiation is biologically destructive in many ways.
    • It causes skin cancer and cataracts, suppresses the human immune system, diminishes the yield of many crops, disrupts the aquatic food chain by killing micro-organisms on the ocean surface and many other negative effects which is still undiscovered.

This is happening due to certain recent human activities which have injected certain chemicals in the stratosphere which consume ozone and reduce its concentration.

Depletion is mainly caused by chlorofluorocarbons (CFCs), halons, methyl chloroform and carbon tetrachlorides.

These chemical substances are mainly either chlorine or bromine which can reach the stratosphere and catalytically break down ozone into oxygen.

CFCs are odourless, non-flamable, non-corosive and nontoxic.

For this reason, scientist originally believed CFCs could not possibly have any effect on the environment. That is why it is widely used in refrigeration and air conditioning, in foam and plastic manufacturing and in aerosol sprays.

Not only is the ozone layer thinning, in some places it has temporarily disappeared. A hole in the layer has developed over Antarctic since 1979 and that hole has persisted for a longer and longer time every year. In 1988, an ozone hole was found over the Arctic for the first time and it too has lasted longer and longer each year since then.

Can we prevent this disaster? It needs certain actions both at individual as well as governmental level.

Since the last two decades, certain actions have been initiated at global level. Important ones are –

  • Montreal Protocol of 1987
  • London Conference of 1992

In both these conferences it was decided that the developed countries would totally ban CFC production by 2000 and the developing countries by 2010AD. Even if it is sincerely followed and strictly implemented by all the 150 countries including India, who are signatory to Montreal Protocol even then the chlorofluorocarbon and chlorine shall continue their influence for another 100 years.

Therefore, all over the world research efforts are continuing for development of substitutes of CFC as coolants for refrigerators and air conditioners.

Acid Rain

The term ‘acid rain’ refers to the deposition of wet or dry acidic materials from the atmosphere on the earth’s surface.

Although most conspicuously associated with rainfall, the pollutants may fall on the earth’s surface either in the form of snow, sleet, hail or fog or in the dry form of gases or particulate matter.

Sulphuric acid and nitric acid is considered as the principal agents responsible for acid rain.

The major culprit are human beings. Smokes emitted from the industries is the major source of sulphur dioxide whereas smokes emitted from the motor vehicle is the major source of nitrogen oxide. These emissions mixed with atmospheric moisture form the sulphuric acid and nitric acids which, sooner or later precipitate on earth in various form.

Acidity is measured on a pH scale based on the relative concentration of hydrogen ions. The scale ranges from 0 to 14, where the lower end represents extreme acidity and the upper end extreme alkalinity.

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A pH Scale

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Acid rain is associated with various forms of precipitation. It we look at rainfall in clean and dust free air, a pH value varies between 5.6 to 6.0, which is slightly acidic in nature. Whenever or wherever the pH value is below 5.6, then the damage becomes noticeable.

The long – term effects of acid precipitation on human health and agricultural production have not yet been ascertained precisely. However, the most conspicuous damage is being done to aquatic ecosystem.

The ecosystem of a stream or lake may be severely affected when its pH falls below 5.

  • Total biomass in such systems is reduced from two to ten times because few organisms can tolerate acid. The diversity of species also decreases.
  • The most severe effect of acidification is on fish. Acidic conditions affect the reproductive capabilities of fish, resulting in a slow decline of fish population. This has been documented in various parts of Europe and North America. In Norway, thousands of lakes and streams have largely lost their fish population, over an areas of 33,000 square kilometer. Several lakes in Eastern United States and Canada have become biological deserts during the last quarter century.

The precise effects of acid rain on forest are not clearly understood, evidence, however, shows that it is responsible for forests die-back which is occurring in each continent. Forest die-back is a German word which means death or decline of forest. Even buildings and monuments are being destroyed because acid deposition accelerated erosion capacity.

Acid rain is a serious global problem and its impact can spread over long distances from the origin of the pollutant. That is why Scandinavian countries complain about British pollution in Europe whereas Canadians blame United States in North America.

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Bibliography : NIOS Geography Book

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