Climate Simulation and Prediction - Climate Dynamics - page 182

which are indicated by flux arrows labeled with compounds such as CO 2 ,
N 2 O, and CH 4 .

THE CARBON CYCLE

To simulate atmospheric CO 2 concentrations interactively in a model, the car-
bon cycle must be included. Figure 12.2 is a schematic overview of the global
carbon cycle with estimated reservoirs and fluxes of carbon.
By far, the greatest reservoir of carbon on the planet is the earth's litho-
sphere , which consists of the crust and the upper mantle, where carbon consti-
tutes 0.032% of the mass. The world's oceans are estimated to contain 38,000
Pg of carbon (PgC, with 1500 PgC sequestered in soils and 560 PgC in plants.
About 4000 PgC remains in unused fossil fuels, in the form of coal, petroleum
(crude oil, oil shale, oil sands), and natural gas. The atmosphere currently con-
tains approximately 830 PgC. 1

plant
respiration
60 Pg/yr

volcanos
0.1 Pg/yr

Atmosphere
750 Pg

soil
respiration
60 Pg/yr

photosynthesis
120 Pg/yr

deforestation and
land use change
0.9 Pg/yr

ocean loss
90 Pg/yr

burning fossil fuels
6 Pg/yr

ocean
uptake
92 Pg/yr

Plants
560 Pg

litterfall
60 Pg/yr

rivers
0.8 Pg/yr

Soils
1,500 Pg

Fossil fuels
4,000 Pg

Earth's crust
100,000,000 Pg

Oceans
38,000 Pg

burial to sediments
0.1 Pg/yr

Figure 12.2 Estimated reservoirs and fluxes of the global carbon cycle. (NASA GLOBE program:
www.nasa.gov.)

1 The conversion from units of PgC to an atmospheric CO 2 concentration in ppm as shown in
Fig. 10.1 is as follows: 1 ppm CO 2  7.822 Pg of CO 2  2.134 Pg of C.