Destruction of rainforests lead to global warming by increasing the AMOUNT of carbon dioxide which is a major greenhouse gas.

Explanation:

• The global average temperature is regulated by various factors, one among them is the amount of carbon, present in the form of carbon dioxide in the atmosphere.
• Carbon forms the basis of life, but too much of carbon dioxide in the atmosphere is harmful because carbon dioxide is a major greenhouse gas which traps the sunlight inside the earth and does not lets the SHORTER wavelengths of heat to escape the earth's atmosphere (Greenhouse effect).
• Thus heat gets trapped in the atmosphere and increases the temperature of the earth.
• Forests, especially rainforests acts as one of the largest reserves of the carbon. But when forests are cut down and it is BURNED it releases massive amounts of carbon in the form of carbon dioxide in the atmosphere of the earth.
• This released carbon dioxide again causes the greenhouse effect, that is heating the earth's atmosphere and causes global warming.
• Hence, we not only need to CONSERVE our rainforests but also should try to SWITCH over green fuels instead of fossil fuels to reduce the carbon emissions.