Answer – A greenhouse gas (GHG) is a gas in an atmosphere that absorbs and emits radiation within the thermal infrared range. This process is the fundamental cause of the greenhouse effect.

The primary greenhouse gases in Earth’s atmosphere are water vapour, carbon dioxide, methane, nitrous oxide, ozone, and chlorofluorocarbons.

• Water vapour contributes to 36-72% of Greenhouse effect.
• Carbon Dioxide (CO2) arises from burning fossil fuels and as a result of deforestation. It contributes to 9-26% of Greenhouse effect. It is the primary greenhouse gas emitted through human activities.
• Methane (CH4), also called “Marsh gas”, arises from rice paddies, wetlands, enteric fermentation in cattle, burning of wood, and landfills. It is responsible for about 4-9% of Greenhouse effect.
• Nitrous Oxide (NO2) contributes (5%) which arises from coal burning, biomass burning, and breakdown of chemical fertilizers.
• Chlorofluorocarbons (CFCs) and their replacements (15%) are 1000 times more heat absorbent than carbon dioxide. They reach the atmosphere from refrigeration
and air conditioning, aerosol sprays, and foam packaging industry.
• Ozone contributes to 3-7% of Greenhouse effect. The largest net source of tropospheric ozone is influx from the stratosphere. Large amounts of ozone are also produced in the troposphere by photochemical reactions, the amounts
increasing with high levels of air pollution.