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Global Issues


Loss of biodiversity and exploitation of natural resources have resulted in ecological imbalances which are major global issues.

Greenhouse Effect and Global Warming

Greenhouse effect refers to warming of earth’s surface due to an increase in the greenhouse gases, particularly carbon dioxide in the atmosphere. [Greenhouse is a glasshouse where delicate and exotic plants are maintained. The air inside the glasshouse is generally warmer than the air outside, though the interior receives less solar radiation.]

Glass walls, carbon dioxide and water vapours are responsible for the greenhouse effect inside the glasshouse. Carbon dioxide and water vapours allow short-wave solar radiations to pass through them but obstruct the passage of long-wave radiations emitted by the surface of the earth. This makes the greenhouse air warmer than the outside air.

Greenhouse gases

Greenhouse gases The heat from the sun passes through the atmosphere. Some of this heat is trapped by certain gases such as carbon dioxide (60%), methane (20%), CFCs (14%), nitrous oxide (6%) etc. in nature. These gases are called greenhouse gases. The atmosphere absorbs much of the incoming radiation from the sun and re-radiates to the earth’s surface and prevents the heat of the earth from escaping into the space. Thus, the atmosphere acts as a greenhouse to trap the heat. This is a naturally occurring phenomenon which is essential, or else the earth would not be warm enough for us to live. But if this greenhouse effect is more than required, it makes the earth warmer than usual. The natural gases in the atmosphere most responsible for keeping the earth’s surface warm are carbon dioxide and methane.


Source of Greenhouse Gases




Greenhouse Gas

Main Sources

Carbon dioxide (CO2)

Fossil fuel burning, wood fuel, deforestation, cement manufacture

Methane (CH4)

Release oil or coal production or transmission enteric fermentation from ruminants (sheep, cattle)

Wetland rice cultivation

Burning and decay of biomass

Chloroflurocarbon (CFC)

Use of solvents, refrigerants, aerosol spray propellants, foam packaging

Nitrous oxide (N2O)

Fertilisers, fossil fuel burning, tropical deforestation, wild fires, forest fires land conversion for agriculture.

Effects of global warming

  • If the concentration of greenhouse gases is within limits, the global system is not affected. But, by increasing the concentration of greenhouse gases and by adding new greenhouse gases such as CFCs, there is an increase in the global temperature. It may lead to melting of ice caps, increase in the sea level and submergence of coastal land.
  • Water balance: The water availability is likely to be more serious and perhaps more expensive to solve. In future, the warmer world will have water crisis in some parts while in other regions it will be wetter than today. Global warming may even affect future rain pattern that may have pronounced effect on agriculture and ecosystem.
  • Change in forests: Temperate and subarctic forests will get reduced to grasslands and shrublands. Forest fire would add more CO2 to atmosphere.
  • Weather extremes: Due to global warming, continuous heat waves and droughts would become a regular problem in many areas. As the upper layer of sea water becomes warmer, hurricanes and typhoons would occur more frequently and blow more fiercely.
  • Threats to human health: Global warming would disrupt supplies of food and water and displace many people by altering disease pattern. Tropical diseases such as malaria, elephentiasis, yellow fever and dengue fever may spread from the tropics to temperate zones. Sea-level rise could spread infectious diseases by flooding sewage and sanitation systems in coastal cities.

Ozone Layer Depletion


Ozone is a condensed form of oxygen formed by three atoms of oxygen. It forms a protective layer in the stratosphere. Ozone is continuously formed by the action of sunlight on oxygen. Some oxygen molecules absorb energy from the sun’s ultraviolet rays and split to form single oxygen atoms. These atoms (O) combine with the oxygen molecules (O2) to form ozone (O3). The amount of ozone in the stratosphere generally remains constant because its formation and destruction occur at the same rate.

Ozone layer protects us from the ultraviolet radiations of the sun which is harmful to most of the living things. If there is ozone depletion, more of ultraviolet radiation hits us.

Ozone depletion was first detected in the stratosphere over Antarctica. The part of the atmosphere where there is ozone depletion is referred to as ozone hole which is not really a hole. Ozone measurement is done by using an instrument called total ozone mapping spectrometer (TOMS).

 Ozone depletion is caused due to aerosols and sulphates emitted by volcanic eruptions and several factories. CFCs, also called freons used in air conditioners and refrigerators, destroy ozone. CFCs cross the ozone layer and interact with the ultraviolet rays during which chlorine is separated. This chlorine destroys the ozone layer.

 Ozone loss allows more radiations to reach the earth. It affects plant growth and fish production. It may cause skin cancer, cataract and may even affect the immune system of the body. UV radiations affect phytoplanktons which are the producers that occupy the first trophic level in the food chain. It would disturb the aquatic ecosystem. CFCs persist for many years in the atmosphere and, therefore, have a long lasting effect on the biotic community.

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