Here's why:

* Incoming solar radiation: The sun emits a wide range of electromagnetic radiation, including visible light, ultraviolet (UV) radiation, and infrared radiation. Much of this radiation reaches Earth's surface.

* Earth's surface absorbs energy: Earth's surface absorbs the solar radiation, warming up.

* Earth re-emits radiation: As the Earth warms, it emits its own radiation, primarily in the form of infrared radiation.

* Greenhouse gases trap infrared radiation: Greenhouse gases in the atmosphere, like carbon dioxide, methane, and water vapor, are good at absorbing infrared radiation. This absorption prevents some of the infrared radiation from escaping back into space.

* Warming effect: As a result of the trapped infrared radiation, the Earth's lower atmosphere and surface become warmer than they would be without the greenhouse effect.

In essence, the greenhouse effect acts like a blanket, preventing some of the heat from escaping back into space, contributing to the Earth's overall temperature.