Land Use and Geo-Engineering - Introduction to Carbon Capture and Sequestration - page 519

Section 1
Introduction
In Chapters 2 and 3, we discussed the lifetime of a CO 2 molecule in the
atmosphere. We have seen that, although the exchange between CO 2 in
the atmosphere and on the surface of the ocean is very rapid, the subse-
quent mixing of the CO 2 -saturated surface layer with the deep parts of
the oceans occurs on a time scale of over two hundred years. This multi-
hundred year time scale assumes atmospheric CO 2 concentrations are
suffi ciently low to not exceed the buffering capacity of the ocean. If the
buffering capacity is exceeded, it will take ten thousand to a hundred
thousand years for the carbon-cycle reactions to have restored the
atmospheric CO 2 levels to equilibrium values.
The extraordinary time scales associated with the carbon cycle make
the ramifi cations of CO 2 emissions very different from those of anthropo-
genic emissions of other gasses. For example, fl ue gas components such
as SO x and NO x , the principal components of acid rain, can be readily
removed with available technologies. Historically, once fl ue gasses were
cleaned of these components, acid rains diminished and within a few
years the problems associated with acidifi cation were mitigated. Similarly,
the ban of chlorofl uorocarbons (CFCs) has already led to some reduction
of the polar ozone hole as the existing CFCs are slowly decomposing in
the atmosphere. On the other hand, if we were to halt all CO 2 emissions
today, it would take hundreds to thousands of years for CO 2 levels to
return to pre-industrial values! In the previous chapters, we discussed
techniques to reduce or at best stop CO 2 emissions. At present, these
technologies have not been implemented on a scale broad enough to
mitigate climate change. For this reason, we may need to employ tech-
nologies that decrease the existing CO 2 levels in the atmosphere. As we
will see, these techniques involve large-scale human intervention in pro-
cesses of the earth: geo-engineering .
No doubt some of our readers feel that we have already geo-
engineered our planet enough. Indeed, we are in the middle of two ongo-
ing global geo-engineering projects. The fi rst experiment, using fossil
fuels for energy, burns the carbon that nature has sequestered in plants
over millions of years in a period of a few hundred years. The other