Geoscience Reference
In-Depth Information
500
A
480
Projecter trends:
460
440
B
420
400
380
360
340
320
Estimates of
C
al
lendar
Mauna Loa
observations
300
Siple ice core
280
Machta
260
1800
1820
1840
1860
1880
1900
1920
1940
1960
1980
2000
2020
2040
2060
Year
Figure 2.5
Estimated carbon dioxide concentration: since
AD
1800 from air bubbles in an Antarctic ice
core, early measurements from 1860-1960; observations at Mauna Loa, Hawaii, since 1957; and projected
trends for this century.
Source: After Keeling, Callendar, Machta, Broecker and others.
Note: (a) and (b) indicate different scenarios of global fossil fuel use (IPCC, 2001).
for some 18 percent of the greenhouse effect.
Cattle populations have increased by 5 percent/
year over 30 years and paddy rice area by 7
percent/year, although it is uncertain whether
these account quantitatively for the annual
increase of 120ppbv in methane over the
past decade.
Table 2.4
, showing the mean
annual release and consumption, indicates the
uncertainties in our knowledge of its sources
and sinks.
300
280
CO
2
260
240
2.5
220
0
200
°C
-2.5
180
-5.0
•
Nitrous oxide
(N
2
O), which is relatively inert,
originates primarily from microbial activity
(nitrification) in soils and in the oceans (4 to 8
×
-7.5
-10.0
10
9
kg N/year
from industrial processes. Other major
anthropogenic sources are nitrogen fertilizers
and biomass burning. The concentration of
N
2
O has increased from a pre-industrial level
of about 285ppbv to 320ppbv (in clean air). Its
increase began in around 1940 and is about
0.8ppbv/year (
Figure 2.8A
). The major sink of
N
2
O is in the stratosphere, where it is oxidized
into NO
x
.
10
9
kg N/year), with about 1.0
×
160
80
Thousands of years (BP)
120
40
0
Figure 2.6
Changes in atmospheric CO
2
(ppmv:
parts per million by volume) and estimates
of the resulting global temperature deviations from
the present value obtained from air trapped in ice
bubbles in cores spanning 160,000 years at Vostok,
Antarctica.
Source: Our Future World, Natural Environment Research
Council (NERC) 1989.
