Behind the Forecast: How clouds affect temperatures

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Behind the Forecast: How clouds affect temperatures
On cloudy days, clouds reflect the sun's light into space, keeping much of the energy away from the surface and leading to cooler temperatures. (Source: William Foeste/CNews)

LOUISVILLE, Ky. (WAVE) - Clouds can bring rain or snow, block the sun’s UV rays, or even make a sunrise visually stunning. But how do they impact our temperatures? Well, it depends on the type of cloud and the time of day.

During the day, sunlight heats the Earth. If skies are clear, more heat reaches the ground leading to warmer temperatures. On cloudy days, clouds reflect the sun's light into space, keeping much of the energy away from the surface and leading to cooler temperatures. Clouds reflect 30 to 60 percent of the sunlight that hits them, according to NASA, which is why they appear white.

At night, since there is no reflection, instead of cooling temperatures, clouds help to keep them warmer. This happens when clouds trap the heat and reemit it back towards the planet's surface. With clear skies, the heat can easily travel into space leading to cooler temperatures.

Clouds in the upper levels of the atmosphere are colder than clouds closer to the ground and the planet's surface itself. These clouds trap heat more effectively while radiating less heat into space. This means that upper-level clouds can have an overall net-heating effect on our planet. One study found that these clouds can warm the temperatures as much as 13°F.

Lower-level warm clouds release more energy than cold, upper-level clouds. Low clouds release the same amount of thermal energy as the planet's surface. That means, without low-level clouds, the planet would lose about the same amount of energy to space as the Earth does with these lower clouds.

During the day, low thick clouds (like stratus clouds) can reflect as much of 90% of light while high thin clouds (like cirrus clouds) can reflect as low as 10% of incoming radiation.

Clouds as a whole have a net cooling effect of about 9°F on our climate.

A change in our climate could lead to a change in clouds and, in turn, global temperatures.

The clouds themselves aren't the only thing that can affect temperatures. The precipitation they produce can also play a role.

The law of conservation of energy dictates that the energy Earth absorbs from the sun must be equal to the amount radiated back into space. Clouds affect both sides of this balance by trapping heat and reflecting incoming energy from the sun. When water vapor evaporates from the Earth's surface, there is a net cooling effect at the surface. A change in the amount or type of clouds would change the energy balance and the water exchanges across the atmosphere.

NASA research found that without clouds, our planet would absorb almost 20 percent more heat. To be in radiation balance, the planet would have to be 22°F warmer than it is now.

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