Clouds have a complex relationship with heat, influencing both the amount of solar radiation reaching the Earth's surface and the amount of heat escaping back into space. They don't simply "stop" heat, but rather modify its flow.
How Clouds Affect Heat
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Blocking Solar Radiation: Clouds, especially thick ones, significantly block incoming solar radiation (light and heat) from the sun. This leads to cooler temperatures on the ground, a phenomenon easily observed on cloudy days. As noted by NASA Climate Kids and numerous other sources, this cooling effect is a primary function of clouds.
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Trapping Heat: Conversely, clouds can also trap heat already present near the Earth's surface. This is similar to how a blanket keeps you warm. This effect is more pronounced with low-lying, dense clouds. The reference from Reddit's r/NoStupidQuestions highlights this aspect, specifying that thick cumulus clouds are particularly effective at retaining heat.
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Net Cooling Effect: Despite their heat-trapping capabilities, the overall net effect of clouds on Earth's climate is a cooling effect. The International Satellite Cloud Climatology Project (ISCCP) data indicates clouds cool the Earth's surface by approximately 5°C (9°F). This is because the cooling effect from blocking solar radiation outweighs the warming effect from trapping heat.
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Altitude and Cloud Type Matter: The impact of clouds on temperature varies based on their altitude and composition. High-altitude, thin cirrus clouds, for instance, allow much of the sun's radiation to pass through but are effective at trapping outgoing heat, resulting in a warming effect. This is discussed in the research from Imperial College London on aircraft-produced clouds.
In summary: Clouds don't simply stop heat; they act as both a shield, reducing incoming solar radiation, and an insulator, trapping some outgoing heat. The net effect is typically a cooling of the Earth's surface, although specific circumstances can lead to localized warming.
