The heat that builds up in the greenhouse effect initially enters the atmosphere as

Solar radiation

Explanation:

Gases such as methane , ozone, and Carbon dioxide are known as the greenhouse gases. When the gases are heated up they usually build up in the greenhouse effect and after a while they enter the atmosphere as solar radiation.

It is important to note that the release of the gases is usually the first(initial) release of the gases into the atmosphere.

infrared radiation within the sun's radiation.

Explanation:

The solar radiation that gets to earth contains about 3 electromagnetic waves which includes visible rays, infrared rays, ultraviolet rays. Infrared rays carries heat through space and is the part of the solar radiation that carries heat into the earth's atmosphere.