Final answer:
Cloudy nights are warmer because clouds act as a thermal blanket, trapping heat and reducing the amount of heat that escapes into space. This results in more warmth being retained near the Earth's surface.
Step-by-step explanation:
Cloudy nights are generally warmer than clear ones because of the role clouds play in trapping heat. During the night, the Earth's surface cools by radiating heat into space. Clouds have a lower emissivity than land or water surfaces, which means they are not as efficient at radiating heat into space. Instead, they reflect some of the heat radiation back toward the Earth's surface. This reflection reduces the heat transfer into dark space and allows the surface to retain more warmth. Therefore, the correct answer to why cloudy nights are warmer than clear ones is: d) Clouds trap heat. This process is similar to how a blanket keeps you warm by trapping your body heat. Clouds act as a blanket in the Earth's atmosphere, inhibiting heat from escaping into the coldness of outer space.