Cloud Greenhouse Forcing: Warming Longwave Radiation Longwave radiation 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. This process is called"cloud greenhouse forcing"and taken by itself, tends to cause a heating or positive forcing" of the earth's climateCloud Greenhouse Forcing: Warming Longwave radiation 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. This process is called "cloud greenhouse forcing" and, taken by itself, tends to cause a heating or "positive forcing" of the Earth's climate