Geoscience Reference
In-Depth Information
1964-1980
Arctic also (see Box 2.1 ). The type of circulation
responsible for this transfer is not yet known with
certainty, although it does not seem to be a simple
direct one.
The water vapor content of the atmosphere is
closely related to air temperature (see B.2, this
chapter, and Chapter 4B and C) and is therefore
greatest in summer and in low latitudes. There
are, however, obvious exceptions to this general-
ization, such as the tropical desert areas of the
world.
The carbon dioxide content of the air, which
averaged 387 parts per million (ppm) in 2007, has
a large seasonal range in higher latitudes in the
northern hemisphere associated with photo-
synthesis and decay in the biosphere. At 50
90°N
300
450
60°
30°
30°
32 5
60°
90°S
J
FM
A
M
J
J
A
S
O
N
D
1984-1993
90°N
N,
the concentration ranges from about 380ppm in
autumn to 393ppm in spring. The low summer
values are related to the assimilation of CO 2 by the
cold polar seas. Over the year, a small net transfer
of CO 2 from low to high altitudes takes place to
maintain an equilibrium content in the air.
°
425
60°
30°
30°
7 Variations with time
The quantities of carbon dioxide, other green-
house gases and particles in the atmosphere
undergo long-term variations that may play an
important role in the earth's radiation budget.
Measurements of atmospheric trace gases show
increases in nearly all of them since the Industrial
Revolution began around 1750 ( Table 2.3 ). The
burning of fossil fuels is the primary source
of these increasing trace-gas concentrations.
Heating, transportation and industrial activities
generate almost 5
60°
300
2 25
90°S
J
FM
A
M
J
J
A
S
O
N
D
Figure 2.3 Variation of total ozone with latitude
and season in Dobson units (milliatmosphere
centimeters) for two time intervals: (top) 1964-
1980 and (bottom) 1984-1993. Values over 350
units are stippled.
Source: From Bojkov and Fioletov (1995) from Journal of
Geophysical Research, 100(D), Fig. 15, p. 16, 548. Courtesy
American Geophysical Union.
pattern must result from a poleward transport of
ozone. Apparently, ozone moves from higher
levels (30-40km) in low latitudes towards lower
levels (20-25km) in high latitudes during the
winter months. Here the ozone is stored during
the polar night , giving rise to an ozone-rich layer
in early spring under natural conditions. It is this
feature that has been disrupted by the stratos-
pheric ozone 'hole' that now forms each spring
in the Antarctic and in some recent years in the
10 20 J/year of energy. Oil and
natural gas consumption account for 60 percent
of global energy and coal about 25 percent.
Natural gas is almost 90 percent methane (CH 4 ),
whereas the burning of coal and oil releases not
only CO 2 but also odd nitrogen (NO x ), sulfur
and carbon monoxide (CO). Other factors
relating to agricultural practices (land clearance,
farming, paddy cultivation and cattle raising)
also contribute to modifying the atmospheric
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