The glass in a greenhouse holds the sun’s warmth inside same as the atmosphere traps the sun’s heat near the earth’s surface and keeps it warm. This is called natural greenhouse effect because it maintains the temperature and makes the earth perfect for life.

In a greenhouse, solar radiations pass through the transparent glass and heat up the soil and the plants. The warm soil and plants emit infrared radiations. Since glass is opaque to infrared radiations (thermal region), it partly reflects and partly absorbs these radiations. This mechanism keeps the energy of the sun trapped in the greenhouse. Similarly, carbon dioxide molecules also trap heat as they are transparent to sunlight but not to the heat radiation. Carbon dioxide is the major contributor to global warming.