The Greenhouse Blanket of Water Vapor
Most people associate deserts solely with extreme heat. However, aridity—a severe lack of moisture—is the true defining characteristic of a desert environment.
In humid climates, ambient water vapor acts as a natural greenhouse blanket. Water molecules absorb infrared thermal radiation emitted by the ground and re-radiate it in all directions, slowing heat escape during nighttime hours.
Rapid Radiative Cooling Over Dry Sand
Desert air contains negligible water vapor, and sand exhibits a remarkably low specific heat capacity compared to water. Sand heats rapidly during sunlight hours but radiates its stored thermal energy directly into space the instant the sun sinks.
With clear skies and near-zero atmospheric humidity to trap departing infrared waves, surface temperatures can plummet by as much as 35°C (63°F) in a single night.