Why can an increase in water vapour reduce night-time temperature fall?

Correct answer: Because water vapour absorbs longwave radiation

Correct answer: A. During the night, the land surface loses energy mainly by emitting longwave, or terrestrial, radiation. Water vapour is a greenhouse gas: it absorbs part of this outgoing longwave radiation and emits radiation in different directions, including back toward the surface. This reduces the net rate at which the surface loses heat, so a humid night is often warmer than a clear, dry night under otherwise similar conditions. The effect does not mean that water vapour creates sunlight or completely prevents cooling; it moderates the fall in temperature. B is nonsensical because day and night are controlled by Earth’s rotation. C is false because water vapour has important radiative properties. D is unrelated to gravity. Memory cue: “Humid air acts like a thermal blanket at night.”