Greenhouse Effect: How the Earth Stays Warm
The glass panes of a greenhouse and the Earth's atmosphere are both transparent to sunlight--they let in the sun's energy. Both also trap heat.
How a Greenhouse Traps Heat
Sunlight passes through greenhouse glass and warms the ground inside. Heat rising from the ground warms the air; the glass prevents the air from escaping, so the greenhouse retains the heat.
How the Atmosphere Traps Heat
Sunlight passes through the atmosphere and warms the planet's surface. Heat rising from the surface warms the atmosphere; gases in the atmosphere absorb some of the heat and reflect it back to the ground. This warming process is called the greenhouse effect.