Global warming is mainly caused by greenhouse gases. The main gases are carbon dioxide (CO2), methane (CH4), Chlorofluorocarbons (CFCs) and nitrogen oxide (N2O).
1. Carbon dioxide (CO2): Carbon dioxide is the main greenhouse gases. The gas contributes over 50% of the greenhouse effect. The following are the source of carbon dioxide in the atmosphere:
(a) Clearing and burning of vegetation.
Green plants, especially woody plants, absorbs
carbon dioxide from the atmosphere as they grow. When the wood dies, the
carbondioxide is released back into the atmosphere. Clearing of forests
(deforestation) and burning vegetation result in the release of carbon dioxide
to the atmosphere . Deforestation remains high in many parts. The loss of the
forest also means that there are fewer trees to absorbs carbon dioxide.
(b) Burning of fossil fuel
Carbon dioxide is a byproduct in the
combustion of fossil fuel such as coal, petroleum. These fossil fuel are burned
in cars, power station and industries.
2. Methane.
The main source of methane is from
agricultural activities. It released from wetlands, such as rice field and from
animals, particular cud-chewing animal like cow. The emission of methane gas
therefore increases with increase agricultural activities.
Methane also produced during the mining of
coal and oil and when vegetation is burnt. Methane molecules have a life time
of 10 years in the atmosphere.