VPE 511: Environment and Environmental Hygiene (2+1)

GREEN HOUSE EFFECT

• The increase in the global mean temperature is called global warming. The global warming is due to increase in green house gases in the atmosphere.
• A green house means a special house in which delicate plants are grown with controlled temperature inside than outside but with less radiation. This is called green house effect which is due to glass walls, high Carbon-di-oxide (Co₂) content and high water vapour in the green house. The green house allows short wave radiations inside but prevent the long wave, i.e, infrared radiations from the earth’s surface. That is why the green house is warmer inside than outside.
• In the same way, green house effect occurs in our environment. Some atmospheric gases allow short wave radiations through them but absorb long wave radiations from the earth and reflect the heat to earth. These gases are called green house gases.

Green House Gases

• The green houses gases include Carbon-di-oxide (CO₂), Oxygen (O₃), Methane, Nitrous Oxide (N₂O), Chlorofluoro carbon (CFC), water vapour and Hydro Fluorocarbons (HFC). The predominant gases are CO₂ and water vapour. About 70 million tons of CO₂ per day are dumped into the earth’s atmosphere.
  • The average global temperature is 15⁰C.
  • If there are no green house gases, the temperature would be – 18⁰C.
  • The green house gases increase the temperature to 33⁰C.
  • The moderate heat trapped by mainly CO₂ and water vapour keeps planet warm enough to allow species to exist.
  • The level of H₂O vapour is constant but CO₂ is increased.
  • Man contributes to the increase of methane, N₂O and CFC’s. This leads to enhanced green house effect.