The Carbon Cycle - Fundamentals of Ecosystem Science - page 111

FIGURE 6.2 Variation in atmospheric CO 2
over three timescales. Panel (a) shows direct mea-
surements of atmospheric CO 2 at Mauna Loa,
Hawaii. The data for panels (b) and (c) come from
ice cores for (b) the Law Dome ice core in
Antarctica and (c) the Vostok ice core in
Antarctica. The x-axis for panel (c) is in years
before present; for panels (a) and (b) the x-axis is
the calendar year. ((a) is drawn from data available
at Dr. Pieter Tans, NOAA/ESRL ( www.esrl.noaa.gov/
gmd/ccgg/trends/ ) and Dr. Ralph Keeling, Scripps
Institution of Oceanography ( scrippsco2.ucsd.edu/ ) ;
(b) is drawn from data available at http://cdiac.ornl.
gov/trends/co2/lawdome.html ( Etheridge et al. 1996 );
and (c) is drawn from data available at http://www.
ncdc.noaa.gov/paleo/icecore/antarctica/vostok/vostok.
html ( Petit et al. 1999 ).)

400

(a)

380

360

340

320

300

1950 1960 1970 1980 1990 2000 2010 2020

Calendar year

360

(b)

320

280

240

1000 1200 1970 1600 1800 2000

Calendar year

(c)

340

300

260

220

180

-400,000 -300,000 -200,000 -100,000 0

Years before present

mostly the combustion of fossil fuel. There are several lines of evidence that, together,
underscore this fact; two are described as follows (see IPCC for further reading at http://
www.ipcc.ch/ ) :

1. Global mass balance. In Table 6.2 we show the major inputs and output of CO 2 to and
from the atmosphere for the decade of 1990 to 2000. We chose this decade because the
numbers were published in a peer-reviewed journal ( Schimel et al. 2001 ) and have been
well vetted. Newer sources list larger anthropogenic inputs ( Field and Raupach 2004 ),
but the basic story has not changed. In Table 6.2 we see that the combustion of fossil
fuel puts about 5.5 Pg of C/y as CO 2 into the atmosphere, with an additional 1Pg

of C/y from land-use changes (basically the cutting of forests, mostly in the tropics;
Dixon et al. 1994 ). This 6.5 Pg C/y anthropogenic source is larger than the observed
rate of increase in the atmosphere (3.1 Pg C/y), so there is more than enough
anthropogenic CO 2 to account for the atmospheric increase. The difference between
CO 2 emissions and the gain in storage in the atmosphere represents C that is either

B