Deserts are defined by extreme temperature fluctuations. They experience a rapid and significant plunge in temperature once the sun sets. Daytime highs often exceed 38 degrees Celsius (100 degrees Fahrenheit), but the absorbed heat vanishes quickly. Nighttime temperatures frequently drop near or even below the freezing point of 0 degrees Celsius (32 degrees Fahrenheit). This wide gap between day and night temperatures results from the desert’s unique atmosphere and the composition of its ground material.
The Atmosphere’s Missing Insulator
The primary driver of the desert’s rapid cooling is the lack of moisture in the air. Humidity, or water vapor in the atmosphere, functions like a thermal blanket for the planet. Water vapor is a potent natural greenhouse gas, effective at absorbing and re-radiating infrared energy, which is heat radiating upward from the Earth’s surface.
In a humid environment, this water vapor captures outgoing heat energy and holds it near the ground, slowing the rate of cooling after sunset. Deserts have extremely low humidity levels, often near zero. Without this insulating layer, heat absorbed by the ground during the day escapes instantly and unimpeded into the upper atmosphere and space.
This process is known as radiative cooling, where the ground and the air shed heat energy as infrared radiation. The air above the desert is typically cloudless, which further accelerates this heat loss. Clouds act as a highly effective barrier, reflecting outgoing radiation back toward the surface. The clear, dry desert skies offer no such obstruction, allowing for maximum heat dissipation and swift cooling.
How Desert Ground Handles Heat
The composition of the desert surface, primarily dry soil, sand, and rock, plays a considerable role in the temperature swing. These materials possess a low specific heat capacity, which measures how much energy a substance can store before its temperature increases. For comparison, the specific heat capacity of water is approximately five times higher than that of dry sand.
Because of this low capacity, desert surfaces heat up quickly when exposed to intense solar radiation during the day. They are poor at retaining that energy once the sun sets. The ground rapidly releases its stored heat back into the atmosphere through radiation.
Conversely, water and moist soil have a high specific heat capacity, requiring much greater solar energy to raise their temperature. This stored energy is released slowly, which is why coastal or tropical areas maintain relatively warm nights. The dry, loose materials of the desert floor facilitate a fast energy exchange, contributing to the extreme daily temperature differences.
Measuring the Diurnal Temperature Range
The phenomenon of the desert getting cold at night is quantified by its diurnal temperature range (DTR). The DTR is the difference between the maximum and minimum air temperatures recorded over a 24-hour period. Deserts have the largest DTRs on Earth, routinely showcasing a temperature variation between 20 and 30 degrees Celsius (36 to 54 degrees Fahrenheit) in a single day.
In the Sahara Desert, summer daytime temperatures can exceed 40 degrees Celsius (104 degrees Fahrenheit), but temperatures can drop to near freezing overnight. The Atacama Desert in Chile, one of the driest places globally, experiences nights that regularly fall below 0 degrees Celsius. This rapid temperature drop often begins immediately after sunset, with the air cooling by as much as 10 to 15 degrees Celsius within a few hours.