I like the small energy cost of this scheme but the difficult question is,
who would like to volunteer to cover their country with pulverized rock?

D. Ocean nourishment

One problem with chemical methods, tree-growing methods, and rock-
pulverizing methods for sucking CO2 from thin air is that all would require
a lot of work, and no-one has any incentive to do it – unless an international
agreement pays for the cost of carbon capture. At the moment,
carbon prices are too low.

A final idea for carbon sucking might sidestep this difficulty. The idea
is to persuade the ocean to capture carbon a little faster than normal as a
by-product of fish farming.

Some regions of the world have food shortages. There are fish shortages
in many areas, because of over-fishing during the last 50 years. The idea
of ocean nourishment is to fertilize the oceans, supporting the base of
the food chain, enabling the oceans to support more plant life and more
fish, and incidentally to fix more carbon. Led by Australian scientist Ian
Jones, the ocean nourishment engineers would like to pump a nitrogen-
containing fertilizer such as urea into appropriate fish-poor parts of the
ocean. They claim that 900 km2 of ocean can be nourished to take up about
5 Mt CO2/y. Jones and his colleagues reckon that the ocean nourishment
process is suitable for any areas of the ocean deficient in nitrogen. That
includes most of the North Atlantic. Let’s put this idea on a map. UK
carbon emissions are about 600 Mt CO2/y. So complete neutralization of
UK carbon emissions would require 120 such areas in the ocean. The map

Figure 31.6. 120 areas in the Atlantic Ocean, each 900 km2 in size. These make up the estimated area required in order to fix Britain’s carbon emissions by ocean nourishment.