radiometers are able to “take the temperature” of clouds, Earth’s water and land sur-
faces, and vertical atmospheric temperature profiles.
There are three scales of temperature in common use. They are Celsius, Kelvin,
and Fahrenheit. The Celsius scale has 100 degrees between the freezing and boil-
ing of pure water at sea level pressure. This is the scale in the most common use in
the world and is the International System of Units (metric system) official scale.
A Kelvin is the same “size” as a degree Celsius but the Kelvin scale has different
zero point. Kelvins are based on absolute temperature. Every molecule vibrates
until it is as cold as absolute zero (− 273 °C), which is defined as 0 Kelvins. Average
room temperature is 293K (22°C). Kelvins are used heavily in the sciences, espe-
cially physics, chemistry, and the atmospheric sciences. The Fahrenheit degree is
about 5/9 the “size” of a Celsius degree and there are 212 degrees between freez-
ing and boiling with 0°F being considerably colder than 0°C. Very few countries
besides the United States use Fahrenheit as their primary temperature scale.
“Official” air temperatures are usually measured in an instrument shelter that is at
about eye height and shades the measurement device from the sun andprecipitation
while allowing the free circulation of air around the instrument. If, for instance, a
measurement device is exposed to the sun, it is measuring the air temperatureplus
absorbing solar radiation increasing the heat content of the device.
The lowest official air temperature near Earth’s surface was− 80 °C in Antarctica
and the hottest was 58°C in Libya. Not all temperature change is related tosolar
energy. Some large temperature changes are associated with the rapid onset and
ebbing of chinook winds; Spearfish, South Dakota experienced a 27°C temperature
rise in twominutes.
Air temperatures are governed by a variety of factors. Although it is true the amount
of solar radiation (controlled by latitude) is key, a number of other factors need to be
considered. They include alocation’sposition in the global circulation system, alti-
tude, surface material properties (specific heat, albedo, etc.), topography (roughness
oflandscape), aspect (direction of slope with respect to the sun), and vegetation. Land
surfaces heat and cool much more rapidly than water in daily and seasonal cycles so
that the most notable temperature extremes are associated with land surfaces.
Where are the coldest places on the planet? In a simple sense, the answer is “the
poles,” but there is quite a difference between the ice-covered Arctic Ocean at the
North Pole and the 2.8 km of glacial ice at the South Pole. Some energy is able to
reach the atmosphere from the Arctic Ocean. Thus, temperatures are significantly
warmer in the North Polar region. In fact, the coldest temperatures in the Northern
Hemisphere are over land in Greenland and northern Siberia. These places are known
as the “cold poles” and have significance in the way wind systems are generated.
Where are the average hottest places on the planet? The equator is the latitude
with the highest average solar angle, but cloudiness prevalent in the intertropical338 Temperature