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    Greenhouse effect 1 Greenhouse effect 1 Presentation Transcript

    • Greenhouse Effect
    • Greenhouse Effect
      • The greenhouse effect is the process in which the emission of infrared radiation by an atmosphere warms a planet's surface.
      • The Earth's average surface temperature is about 25°C warmer than it would be without the greenhouse effect
    • Greenhouse Effect
      • The Earth receives energy from the Sun in the form of radiation.
      • The Earth reflects about 30% of the incident solar flux.
      • The remaining 70% is absorbed, warming the land, atmosphere and oceans.
    • Greenhouse Effect
      • Solar Energy (sunlight) is short-wavelength radiation which easily penetrates the Earth's atmosphere and warms the Earth.
      • Only about one quarter of incoming sunlight is reflected by the atmosphere.
      • The warmed Earth emits long-wavelength radiation (infrared waves or heat energy) back into space.
      • These longer waves are mostly reflected back to Earth by the atmosphere.
    • Greenhouse Gases
    • Carbon dioxide
      • In the last 200 years, because of human activities the proportion of CO 2 has risen from 280 ppm to 360 ppm.
      • The proportion of CO 2 has risen by 27% since the beginning of the industrial revolution, when we started to burn coal rather than wood to fuel civilization.
      • At present, it is increasing by about 3 ppm a year.
    • Methane
      • Methane has a much greater warming effect, about 21 times that of carbon dioxide by volume.
      • Methane has increased 145% over the last 200 years.
      • Despite its greater potential for green house effect, scientists seem less bothered about the rise in methane than that of carbon dioxide.
      • The reason is that carbon dioxide survives longer in the atmosphere than methane (between 50 and 200 years)
      • Methane is destroyed by chemical processes within 12 – 17 years.
    • Nitrous Oxide
      • Nitrous oxide is over 200 times more powerful greenhouse gas than CO 2 on a per molecule basis.
      • Its greenhouse role is minor compared with other greenhouse gases, but has a relatively long atmospheric life of 120 years.
      • The volume is steadily growing at about 0.25% a year.
      • The gas is produced in the ground following the application of ammonia based fertilizers.
      • Various industrial processes also gives off nitrous oxide.
    • Chlorofluro carbons
      • CFCs were invented by Thomas Midgley in 1930 and has been extensively used in refrigerators and air conditioners all over the world.
      • It has also been used to blow foams and aerosol sprays.
      • A CFC molecule added to the atmosphere has a greenhouse effect 5000 times greater than that of an added molecule of CO 2 .
      • This means that despite their tiny concentration, compared with CO 2 , they have a significant impact.
      • They have a long life span of 100 years.
    • Ozone
      • Ozone acts as a shield in the stratosphere, protecting us from the harmful effects of UV rays.
      • But in the troposphere it function as a green house gas.
      • Emission of oxides of nitrogen and hydrocarbons from power stations and vehicles is increasing the concentration of Ozone in the lower atmosphere.
      • It has been calculated that a doubling in its concentrations throughout the entire troposphere would lead to a one degree increase in surface air temperature.