An Introduction to Environmental Chemistry

tification of the various fuel types burned every year and a knowledge of the

amount of CO 2 each produces on combustion. This latter factor, although well

known, varies quite a lot between fuels. For example, for each unit of energy pro-

duced, coal forms 25% more CO 2 than oil and 70% more than natural gas. This

occurs because, in the combustion of gas and oil, a major proportion of the energy

comes from conversion of hydrogen atoms (H) in the fuel to water (about 60%

Global Change 249

1950s and 1960s), can then be used to
estimate the rates at which CO 2 is exchanged
between the atmosphere and surface ocean,
its diffusion into the deep ocean and its
transport by vertical circulation.
For the well-mixed reservoirs, a
conservation equation is written in which
gain of^14 C by inflow to the box (atmosphere
or surface ocean) is balanced by the outflow
to other boxes plus radioactive decay (see
Section 2.8) of the tracer during its time in
the reservoir. For the deep ocean,
conservation is described by a partial
differential advection–diffusion equation. The

diffusion coefficient is chosen to best fit the

measured depth profile of^14 C in the oceans.

Using the model, the uptake of fossil fuel

CO 2 can be estimated by integrating forward

in time from an assumed pre-industrial

steady-state value, while adding to the

model’s atmosphere the estimated year-by-

year release of CO 2 from fossil-fuel burning.

At each time step, the fluxes of carbon

between the various boxes are calculated

and the carbon contents and concentration

profiles changed accordingly. From such

models it is calculated that about 35% of

anthropogenic CO 2 is absorbed by the oceans.

CO

concentration (ppm) 2

0 2 4 6 8 10 12 14

320

325

330

335

340

345

350

355

360

365

Days after iron added

Mean CO 2 air

CO 2 water

Inside the patch

Outside the patch

Fig. 7.4Surface seawater CO 2 concentration during an iron-fertilization experiment. After

Watson et al. (2000).