The overall effect of all clouds together is that the Earth's surface is cooler than it would be if the atmosphere had no clouds.

The shortwave rays from the Sun are scattered in a cloud; many of the rays return to space. The resulting “cloud albedo forcing,” taken by itself, tends to cause a cooling of the Earth.

When a cloud absorbs longwave radiation emitted by the Earth’s surface, the cloud re-emits a portion of the energy to space and a portion back toward the surface. The intensity of the emission from a cloud varies with its temperature and also depends upon several other factors, such as the cloud’s thickness and the makeup of the particles that form the cloud.
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This process is called “cloud greenhouse forcing” and, taken by itself, tends to cause a heating or “positive forcing” of the Earth’s climate. Usually, the higher a cloud is in the atmosphere, the colder is its upper surface and the greater is its cloud greenhouse forcing.