Geoscience Reference
In-Depth Information
(a)
(b)
400
380
380
360
360
340
340
320
320
1960
1970
1980
1990
2000
2010
1975
1985
1995
2005
2015
Year
Year
(c)
(d)
310
360
South pole
Siple
Adélie Land, Antarctica
Mauna Loa, Hawaii
Law Dome, East Antarctica
340
270
320
230
300
190
280
150
260
0
100 200
Age of entrapped air (kyr BP)
300
400
900
1100
1300
1500
1700
1900
2100
Year
Figure 10.1 (a) Direct atmospheric CO
2
measurements from the (a) Mauna Loa Observatory and
(b) South Pole. (c) Values for 400,000 years of atmospheric CO
2
from the Vostok, Antarctica, ice core.
(d) Values of atmospheric CO
2
for the last 1100 years from various ice cores and Mauna Loa.
These observed changes in the atmospheric CO
2
concentration are known to
be the result of human activity. Studies of isotopic ratios of atmospheric CO
2
,
as well as analyses of records of fossil fuel use and land clearing, prove that the
added CO
2
in the atmospheric is of anthropogenic origin.
2
The largest source of anthropogenic atmospheric CO
2
is the burning of fos-
sil fuels, which converts organic carbon into CO
2
gas. This source is currently
estimated at 6 Pg/yr.
3
The trend in rates of fossil fuel burning is similar to that
of the atmospheric CO
2
concentration, that is, exponentially increasing, and
the excess carbon in the atmospheric has an isotopic signature that confirms
its origin. Additional sources of atmospheric CO
2
are forest clearing and other
anthropogenic changes in the land surface (~1.0 Pg/yr) and cement manufac-
turing (~0.1 Pg/yr). Only about half the CO
2
released by human activity re-
mains in the atmosphere; the rest is absorbed by the ocean (~1.9 Pg/yr) and
2
The
13
C/
12
C ratio of fossil-fuel CO
2
is about 2% lower than that of the pre-industrial atmosphere.
3
The unit Pg is petagrams of carbon, or 10
15
g of carbon; 1 Pg is equivalent to 1 Gt (gigaton),
or 10
9
or 1 billion metric tons of carbon.
