Page 1 - LN
P. 1

SAI International School
                                                 Subject - Chemistry
                                                       Class - VIII
                                       Topic – COMBUSTION AND FLAME
                               Sub-Topic-Green House Effect;Global warming


                                                   LESSON NOTES
        Green House effect
        The greenhouse effect is the process by which radiations from the sun are absorbed by the
        greenhouse gases and not reflect into space. This insulates the surface of the earth and
        prevents it from freezing.

        A greenhouse is made of glass that can be used to grow plants. The sun’s radiations warm the
        plants and the air inside the greenhouse. The heat trapped inside can’t escape out and warms
        the greenhouse which is essential for the growth of plants.

        The same is the case in the earth’s atmosphere. During the day the sun heats the earth’s
        atmosphere. At night, when the earth cools down the heat is radiated back into the
        atmosphere. During this process,the heat is absorbed by the greenhouse gases in the earth’s
        atmosphere. This is what makes the surface of the earth warmer, which makes the survival of
        living beings on earth possible.

        However, due to the increased levels of greenhouse gases, the temperature of the earth has
        increased to a very high level due to several drastic effects. More greenhouse gases mean
        more heat will be absorbed.

        Greenhouse Gas
        The gases that absorb infrared radiation and create a greenhouse effect are called
        greenhouse gases. Some of the major greenhouse gases are water vapour, carbon dioxide,
        methane, ozone, nitrous oxide, chlorofluorocarbons (CFC).

        The major contributors to the greenhouse gases are factories, automobiles, deforestation, etc.
        The increased number of factories and automobiles increases the amount of these gases in
        the atmosphere. The greenhouse gases never let the radiation to escape from the earth and
        increase the surface temperature of the earth. This then leads to global warming.

        Causes  of the greenhouse effect
        1.  Burning of fossil fuels.
            Burning fossil fuels releases carbon dioxide gas. With the increase in population, the
            utilisation of fossil fuels has increased. This has led to an increase in the release of carbon
            dioxide gas in the atmosphere.
        2.  Deforestation.
            Plants and trees take in carbondioxide and release oxygen. Due to the cutting of trees,
            there is an inconsiderable increase in the level of carbon dioxide gas which increases the
            earth’s temperature.
        3.  Fertilisers.
            Nitrous oxide used in fertilisers is one of the contributors to the greenhouse effect in the
            atmosphere.

                                                                                                            1
   1   2   3