Environmental Science
An important reason for the large daily temperature range over deserts is:

The ozone content of desert air is very low
Free convection cells are unable to form above the hot desert ground
The light-colored sand radiates heat very rapidly at night
Dry air is a very poor heat conductor
There is little water vapor in the air to absorb and re-radiate infrared radiation

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Environmental Science
Although the polar regions radiate away more heat energy than they receive by insolation in the course of a year, they are prevented from becoming progressively colder each year by the:

Conduction of heat through the interior of the earth
Concentration of earth's magnetic field lines at the poles
The insulating properties of snow
Release of latent heat to the atmosphere when polar ice melts
Circulation of heat by the atmosphere and oceans

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