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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 sun’s 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 carbon dioxide 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.
4. Industrial waste.
Industries and factories produce harmful gases that are released in the atmosphere.

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