The Carbon Cycle - Introduction to Carbon Capture and Sequestration - page 128

0.6

0.5

0.4

Ocean Invasion

0.3

Reaction with CaCO 3

0.2

0.1

Reaction with Igneous Rocks

0.0

0 5000 10000 15000 20000 25000 30000 35000 40000

Year (A.D.)

Figure 3.6.3 CO 2 absorption mechanisms
Upon the invasion of CO 2 from fossil fuels into the ocean, the acidity from the CO 2
provokes the dissolution of CaCO 3 from the sea fl oor. It takes thousands of years for the
dissolution of CaCO 3 to restore the pH of the ocean to a natural value. Restoring the pH
also replenishes the buffering ability of sea water to store more CO 2 , so the airborne
fraction of the fossil fuel CO 2 drops a bit further [3.13]. At the end of the neutralization
stage, the atmosphere still contains more CO 2 than it held before the fossil fuel era. The
rest of the CO 2 awaits reaction with igneous rocks. CO 2 is extracted from the atmos-
phere by these reactions and ends up on the sea fl oor in CaCO 3 deposits. This fi nal
piece of the anthropogenic CO 2 perturbation takes hundreds of millennia to subside.
Figure adapted from [3.12].

Given these results, the next step is to address the relationship
between these predicted atmospheric CO 2 levels and average tempera-
tures on the surface of the earth. We have seen that in the early days of
the earth, CO 2 levels were much higher than they are now. We will use
some of the data that have been collected about these conditions to
understand potential impacts of future CO 2 levels.

Paleocene-eocene thermal maximum

Figure 3.6.5 shows a compilation by the IPCC of different sources of
experimental data on atmospheric CO 2 levels for the past millions of
years [3.15]. In Box 3.6.1 we introduce some of the experimental tech-
niques that have been used to obtain these data. The data in Figure 3.6.5