Greenhouse effect and Global warming

Environmental Studies

Greenhouse effect and Global warming:

Greenhouse means a building made of glass with heat and humidity regulated for growing plants. In it visible light passes through the glass and heats up the soil warming the plants. The warm soil emits radiation in longer wave lengths, i.e. infrared. As the glass is opaque to longer wavelength of infrared radiation it partly reflects and partly absorbs these radiations. Due to this mechanism the greenhouse is warmer than the outer atmosphere.

The earth’s atmosphere acts like a greenhouse where CO2 acts like a greenhouse gas which transmits shorter wavelength solar radiation but reflect the longer wavelength heat radiation coming from warmed surface of the earth. CO2 molecules are transparent to sunlight but not to heat radiation. So they trap and reinforce the solar heat stimulating an effect popularly referred to as greenhouse effect.

The 4 major greenhouse gases are carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O) and chlorofluorocarbons (CFC)

The contribution of greenhouse gases is as under

  • CO2 = 55%.

A COmolecule remains in the atmosphere for about 50-250 years which is the maximum span of any greenhouse gas.

  • CH4 =20%

CH4 traps about 25 times more heat in the atmosphere than a CO2 molecule over a period of 100 years.

  • CFC = 14%

Each CFC molecule can trap heat equivalent to 10,000 molecules of CO2.The life span of CFC’s is 120 years.

  • N2O = 10-11%

The heat absorption capacity of N2O is 250-290 times that of COand it remains in the atmosphere for about 160 years.

Sources of Greenhouse Gases:


  • Power stations based on fossil fuels are the major source of CO2
  • Automobiles, railways and aircraft use large quantity of diesel and petrol releasing huge amount of CO2
  • Deforestation adds to amount of co2 in the atmosphere.
  • A large number of factories burn immense quantity of coal, oil and thus produce carbon dioxide.


It is mainly released from garbage dumps and paddy fields.

  • The rice crop releases through its roots glucose which when acted upon by a group of anaerobic bacteria called methanogenes produces methane.
  • CH4 is also produced from biomass i.e. residue of tress, plants and rice crop


Chlorofluorocarbons are the compounds of chlorine and fluorine eg Freon and Halons

  • Air conditioners, refrigerators. aerosol propellants, fire extinguishers


  • Lightning is a major source of nitrogen oxides. The high temperature and pressure in the air along the path of lightning flash causes the breakup of nitrogen and oxygen molecules into fragments that recombine to form nitrogen oxides.
  • Burning of fossil fuels releases nitrogen oxides
  • Agricultural activity using chemical fertilizers contributes about 15-28% of the nitrogen oxides produced.
  • Some anaerobic fungi also release nitrogen oxide as a by –product during respiration.
  • Nitrogen oxides are also formed during the process of nitrification and denitrification


  • The glaciers are melting and the melted ice raises the sea level thus flooding the low lying regions.
  • There are incidents of occurrence of natural fires due to global warming
  • Global warming also effects the nesting cycle of the birds, altering the habitats, breeding and migration of animals.
  • It affects the agriculture as CO2 is a natural fertilizer and the plants grow larger and faster with increasing CO2 in the atmosphere. This abnormal fast growth of plants might be beneficial as the yield of major crops increases but the soils may become impoverished more rapidly.
  • In temperate regions, the winters are becoming shorter and warmer and the summers will be longer and hotter.
  • There is enormous increase in rainfall but the problems of desertification, drought and soil erosion will further worsen.