Greenhouse Effect ,Ozone Depletion and Pollution

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Greenhouse Effect ,Ozone Depletion and Pollution

  • A greenhouse has glass roof and glass walls and normal floor.
  • Sun SW radiation enters the room unimpeded through these transparent glasses.
  • On hitting the floor, it gets re-radiated as LW radiation
  • LW radiation can’t pass through glass.
  • Trapped LW Radiation raises of temperature of the GH.
  • This is called the Green House effect
  • The Greenhouse effect has twomanifestations:-
    • Weather manifestation
    • & Ecological Manifestation
  • The Weather manifestation occurs when thenights are cloudy because:-.
    • On a unclouded night, the LW re-radiationfrom the earth go in to the space unimpeded.
    • But on a cloudy night, the LW radiation getstrapped by the cloud cover raising the atmospheric temperature.
  • The Ecological manifestation occurs in theform of Global Warming
    • Global warming occurs due to thegreenhouse gases like CO2, water vapor, methane, nitrous oxide, halocarbons andchloroflurocarbons.
    • Suns SW radiation passes through thesegases unimpeded.
    • But LW re-radiation from the earth istrapped and re-radiated back to the earth which raises temperature.
    • Methane and halocarbons trap more energythan CO2.
    • But massive output of CO2 (30billion tonsper anum containing 8 billion tons of carbon) and its long ‘atmosphericlifetime’ (200 years before removal by chemical reaction)  make it the most dangerous. Though photosynthesisand ocean absorb the CO2, annually 3 bn tons is still added to the atmosphere.
    • This concentration continues to increase alarmingly due to increasinghuman activities.
  • One evidence of increase in globaltemperature is the increase in the number of typhoons and cloud bursts.

Ozone Depletion and Pollution

  • Ozone is present in the higher level of the earth’s atmosphere which is essential for shielding the earth against ill-effects of sun’s ultraviolet radiation which can cause skin cancer. In 1974, it was established that CFCs used in Styrofoam insulation, ACs and refrigerators rise to stratosphere, where ultraviolet rays release their chlorine atom.
  • This free chlorine depletes the ozone layer.
  • However data this finding was never taken seriously.
  • 10 years later this matter caught world attention when , ozone layer above the Antarctica was found depleted.
  • 50 countries signed the Montreal protocol in 1987  for complete phase out of CFCs  by 1996.
  • However CFCs continued to be used in older ACs preventing  repair of the ozone hole.
  • By 1998, the ozone hole has been enlarged to 10 million square miles, part of South America being the worst hit.
  • Major worry now is depletion of phytoplankton  in the oceans which is the foundation of all marine life.
  • The Graph below shows the alarming increase in natural disasters which are attributed to global warming.