Chapter 3
Air Temperature
This chapter focuses on the temperature of the air above the Earth’s surface. It examines
air temperature, its measurement, and the factors that cause it to vary through time and
space. This chapter also considers the topic of global warming.
 Five important factors influencing air temperature are:
 insolation
 latitude
 surface type
 coastal versus interior location
 elevation
 Temperature is a measure of the sensible heat of a substance which changes as
energy flows across its surface.
 When the net radiation of a surface – the balance between incoming shortwave and
outgoing longwave radiation – is positive, the surface temperature rises, and when net
radiation is negative, the surface temperature falls.
 Heat energy can be transferred by conduction, by latent heat transfer, and by
convection.
 The daily cycles of insolation and net radiation peak at solar noon, while the daily
cycle of air temperature peaks in the mid-afternoon.
 Air temperature measured above an urban surface is usually higher than that over a
nearby rural surface.
 The troposphere is the lower part of the atmosphere in which temperature declines
with altitude.
 The environmental temperature lapse rate – the rate of temperature change with
altitude – averages 6.4° C per 1000 meters in the troposphere.
 The troposphere is the zone in which most every-day weather phenomena (i.e.
clouds, storms, rainfall, snowfall) occur.
 The top of the troposphere is known as the tropopause and is found about six
kilometers above the surface at the poles and sixteen kilometers above the surface at
the equator.
 In the stratosphere, the absorption of ultraviolet radiation causes the temperature to
increase with altitude.
 Daily air temperature cycles tend to be more pronounced in high elevation
environments.
 In a temperature inversion, the normal situation of air cooling with altitude is
reversed and air warms with altitude.
 Yearly temperature range is greater in high latitude and continental locations and
less at equatorial and coastal locations.
 The world patterns of isotherms are largely explained by latitude, coastal-interior
contrasts, and elevation.
 Six important points about temperature patterns are:
 Temperatures decrease from the equator to the poles.
 Large landmasses in the subarctic and arctic develop centers of extremely low
temperatures in winter.
 Temperatures in equatorial regions change little from January to July.
 Isotherms make a large north-south shift from January to July over continents in
the midlatitude and subarctic zones.
 Highlands are colder than surrounding lowlands.
 Areas of perpetual ice and snow are intensely cold.
 Five important points about temperature range are:
 The annual temperature range increases with latitude.
 The greatest ranges are in the subarctic and arctic zones of Asia and North
America.
 Annual range is moderately large on land in the tropical zone.
 Annual range in coastal areas is less than the range inland at the same latitude.
 Small temperature ranges are found near oceans in the tropical zone.
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Factors affecting global warming and cooling include:
greenhouse gases
tropospheric aerosols
cloud changes
land cover changes
changes in solar output
aerosols from volcanic activity
 The warming effect of the greenhouse gases (carbon dioxide, methane, nitrous
oxides, ozone, and chloroflourocarbons) has exceeded the cooling effect of other
factors since about 1850.
 Observations show both substantial annual variations in the average temperature of
the lower atmosphere and a pronounced trend toward warmer temperatures in recent
years.
 Most scientists agree that the observed atmospheric warming trend is the result of
greenhouse gas emissions from human activities and that the warming trend will
continue into the future.