Low, thick clouds primarily reflect solar radiation and cool the surface of the Earth. High, thin clouds primarily transmit incoming solar radiation; at the same time, they trap some of the outgoing infrared radiation emitted by the Earth and radiate it back downward, thereby warming the surface of the Earth.
When I was reading we ran into the inquiry “Do clouds reflect sunlight?”.
One answer is that clouds, especially, low, thick clouds, reflect incoming sunlight (shortwave radiation) back to space. High clouds reflect less solar radiation and trap longwave, infrared radiation (heat) re-radiated from Earth’s surface. Absorbed radiation is transformed into heat. How do clouds affect sunlight?
How do clouds affect the amount of sunlight on Earth?
Snow and ice, airborne particles, and certain gases have high albedos and reflect different amounts of sunlight back into space. Low, thick clouds are reflective and can block sunlight from reaching the Earth’s surface, while high, thin clouds can contribute to the greenhouse effect.
Because a cloud usually has a higher albedo than the surface beneath it, the cloud reflects more shortwave radiation back to space than the surface would in the absence of the cloud, thus leaving less solar energy available to heat the surface and atmosphere.
To understand why, consider again that summer day: If a big, fluffy cumulus cloud comes drifting by, it’s usually good news for hot cloud-watchers. Low thick clouds cast a refreshing shadow and reflect sunlight back into space. They cool the planet and the people beneath them. On the other hand, high wispy clouds drifting by are less refreshing.
In addition to the warming effect of clear air, clouds in the atmosphere help to moderate the Earth’s tempera- ture. The balance of the opposing cloud albedo and cloud greenhouse forcings determines whether a certain cloud type will add to the air’s natural warming of the Earth’s surface or produce a cooling effect.
Do clouds cool the Earth’s surface?
Well, that depends on where the clouds are in Earth’s atmosphere. Clouds within a mile or so of Earth’s surface tend to cool more than they warm. These low, thicker clouds mostly reflect the Sun’s heat. This cools Earth’s surface.
The balance between the cooling and warming actions of clouds is very close although, overall, averaging the effects of all the clouds around the globe, cooling predominates.
Fewer clouds would open a window through which heat could escape to space and thus cool the planet. Earth, they argued, has a natural response that counteracts rising temperatures — a bit like an iris in a human eye dilating to adapt to low light.