Facts

The Greenhouse Effect

The Greenhouse Effect is a real effect which predates the industrial civilization. Click here for a drawing and more information. It is the enhanced trapping of heat from the Sun due to the presence of certain gases in the atmosphere. If we didn't have these gases (the most important being carbon dioxide - CO2 - water, methane - CH4 - and chlorofluorocarbons - CFC) the average temperature on Earth would be significantly lower, by 33 degrees C according to some models. Venus has a thick atmosphere and the greenhouse effect is particularly strong there, where the surface temperature is 430 degrees C. Mars has a very thin atmosphere (7 % of the one on Earth), although it is rich in carbon dioxide. The Mars temperature is around 240 K (-30 C) and is 10 C higher than if it didn't have any atmosphere.

What scientists and policy makers are concerned about is an accelerated global warming due to the immission into the atmosphere of large quantities of "greenhouse gases", most notably CO2, CH4, and CFC.

Svante Arrhenius, winner of the Nobel Prize in Chemistry, 100 years ago predicted that the pollution introduced by rapid industralization would cause a warming of the Earth. He predicted that the temperature would increase by a few degrees for a doubling of the concentration of CO2 in the atmosphere as a result of fossil and forest burning.

The amount of carbon dioxide has indeed increasd over the years. Samples taken at Manua Loa (Hawaii) and from drilling into ice sheets, have shown an increase of CO2 by 25-30% in the last century. Please click here to see the data. This increase has tracked the increase of the average temperature on Earth, about 0.5 C in the last century.

Sources of Greenhouse Gases

CO2 concentration in the atmosphere increases because of:
  • Burning of fossil fuels, where the carbon in the fuel combines with the oxygen in the atmosphere to form CO2.
  • Deforestation.
  • Industrial processes and transportation.
    • Comments:

    1. It is not yet clear how much of this CO2 is retained in the atmosphere and how much is exchanged with the oceans. It is without doubt, however, that CO2 concentration in air has increased since the first part of 1800s. In the previous 1,000 year, CO2 changed by less than 5%.

    2. CO2 concentration changes seasonally, higher in the fall, lower in the spring. This is due to the change of foliage cover, mostly in the northern hemisphere.

    Methane concentration in the atmosphere has increased because of:

  • Leakages in stages of production/transportation/consumption
  • Rice cultivation
  • Landfills
    • Although the amount of CH4 in the atmosphere is much smaller than the one of CO2, methane is a more efficient greenhouse gas.

    CFC (Chlorofluorocarbons) concentration increased because of its use in electronic industry (to clean computer boards) and in refrigeration systems. The production of CFC is now regulated worldwide, while phasing to alternative fluids is taking place.

    This page was produced by Gianfranco Vidali