Science: Human Impact on Environment: Global Environmental Problems (For CBSE, ICSE, IAS, NET, NRA 2022)

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Global Environmental Problems

The Ozone Hole: Depletion of the Ozone Layer

  • The ozone layer present in the earth՚s atmosphere prevents the entry of sun՚s harmful ultraviolet (UV) radiations reaching the Earth՚s surface. Industrial use of chemicals called chlorofluorocarbons (CFCs) in refrigeration, air conditioning, cleaning solvents, fire extinguishers and aerosols (spray cans of perfumes, insecticides, medicines etc.) damage the ozone layer.
  • Chlorine present in the CFCs on reacting with ozone (O3) layer splits the ozone molecule to form oxygen (O2) . Amount of ozone, thus, gets reduced and cannot prevent the entry of UV radiations. There has been a reduction by 30 - 40 % in the thickness of the ozone umbrella or shield over the Arctic and Antarctic regions. This thinning of ozone layer is called ozone hole.

The Depletion of Ozone Layer May Lead to the Following Hazards

  • Sunburn, fast ageing of skin, cancer of skin, cataract (opaqueness of eye lens leading to loss of vision) , cancer of the retina (sensitive layer of the eye on which the image is formed) .
  • Genetic disorders
  • Reduced productivity at sea and forests

The Damage to the Ozone Layer Can be Prevented By

  • Reducing the consumption of CFCs by adopting alternative technologies (substituting air conditioning gases by non-CFCs)
  • Discouraging the use of aerosol containing spray cans.
Damage to the Ozone Layer


Greenhouse is referred to as a chamber where plants are grown in a closed warm environment as compared to the outside temperature. This is normally practiced in cold region of the hills. The solar radiations bringing heat (in the form of infra-red rays from the sun) are trapped inside the chamber. The atmosphere on earth can also act in a similar way.

Greenhouse Effect

Effects of Global Warming

  • Melting of snow caps/glaciers and rising of sea level.
  • Submerging of coastal areas of the Maldives islands in the Indian Ocean.
  • Unpredictable weather patterns.
  • Early maturation of crops leading to reduced grain size and low yields.
  • Interference with the hatching of eggs in certain fish.


  • Smog is a combination of fog, smoke and fumes released by mills and factories, homes and automobiles.
  • When sunlight falls on stagnant air under low humid conditions in the presence of pollutants such as SO2 soot, nitrogen oxide and hydrocarbons, photochemical smog is formed. (Photochemical: chemical reactions in the presence of light) . Smog stays close to the ground and reduces visibility.
  • Photochemical smog is also called Pan smog due to the production of peroxyacetyl nitrate (PAN) and ozone which form from hydrocarbons and nitrogen oxides in the air in presence of solar radiation. PAN and Ozone are called photochemical oxidants.

Acid Rain

  • Acid rain is caused when nitrogen oxides, SO2 and particulate matter in the atmosphere react with H2O to produce acids.
  • Acid rain is harmful to the environment. It affects life in water and on land. The fish cannot survive in acidic water below pH 4.5. It can also damage trees in the Forests.

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