Geoscience Reference
In-Depth Information
2. The second biological approach is changing the uptake of carbon dioxide by the oceans. The most famous ocean
'technofix' was suggested by the late Professor John Martin. He suggested that many of the world's oceans are un-
derproducing. This is because of the lack of vital micro-nutrients, the most important of which is iron, which allows
plants to grow in the surface waters. Marine plants need minute quantities of iron, without which they cannot grow.
In most oceans enough iron-rich dust gets blown in from the land, but it seems that large areas of the Pacific and
Southern Oceans do not receive much dust and thus are barren of iron. So it has been suggested that we could fertil-
ize the ocean with iron to stimulate marine productivity. The extra photosynthesis would convert more surface-water
carbon dioxide into organic matter. When the organisms die, the organic matter drops to the bottom of the ocean, tak-
ing with it and storing the extra carbon. The reduced surface-water carbon dioxide is then replenished by carbon di-
oxide from the atmosphere. So, in short, fertilizing the world's oceans could help to remove atmospheric carbon di-
oxide and store it in deep-sea sediments. Experiments on this at sea have been highly variable, with some showing no
effects at all while others have shown that the amount of iron required is huge. Also, as soon as you stop adding the
extra iron, most of this stored carbon dioxide is released, as very little organic matter is allowed to escape out of the
photic zone per year.
3. Physical. It is possible to remove carbon dioxide directly from the air. However, considering carbon dioxide makes up
just 0.04 per cent of the atmosphere this is much harder than it sounds. One mad idea is the production of artificial or
plastic trees. Klaus Lackner a theoretical physicist and Allen Wright an engineer, supported by Wally Broecker a cli-
matologist, have designed carbon dioxide binding plastic, which can scrub carbon dioxide out of the atmosphere. The
carbon dioxide is then released from the plastic and taken away for storage. The first problem is water, as the plastic
releases the carbon dioxide into solution when wet, so the plastic trees would have to be placed in very arid areas or
require giant umbrellas. The second problem is the amount of energy required to build, operate, and then store the
carbon dioxide. The third problem is one of scale; tens of millions of these giant artificial trees would be required
just to deal with US carbon emissions.Why not just plant normal trees? However, it is clear that technology to re-
move carbon dioxide at source or ultimately from the atmosphere may be required.
4. Weathering. Carbon dioxide is naturally removed from the atmosphere over hundreds and thousands of years through
the process of weathering, at a rate of 0.1 GtC per year, but this is 100 times less than what we are emitting. Only
weathering of silicate minerals makes a difference to atmospheric carbon dioxide levels, as weathering of carbonate
rocks by carbonic acid returns carbon dioxide to the atmosphere. By-products of hydrolysis reactions affecting silic-
ate minerals are biocarbonates (HCO
3-
), which are metabolized by marine plankton and converted to calcium car-
bonate. The calcite skeletal remains of the marine biota are ultimately deposited as deep-sea sediments and hence lost
from the global biogeochemical carbon cycle for the duration of the lifecycle of the oceanic crust on which they were
deposited.
There are a number of geoengineering ideas aimed at enhancing these natural weathering
reactions. One suggestion is to add silicate minerals to soils that are used for agriculture.
This would remove atmospheric carbon dioxide and fix it as carbonate minerals and
biocarbonate in solution. However the scale this would have to be done is very large and
there are unknown effects on soils and their fertility. Another suggestion is to enhance the
rate of react of carbon dioxide with basalts and olivine rocks in the Earth's crust. Concen-
trated carbon dioxide would be injected into the ground and would create carbonates deep
underground. Again, like many geoenigineering ideas, it is a great suggestion but very
little work has been done to see if it is feasible, safe, and scalable.
5. Solar radiation management. As you can see from earlier discussions in the chapter, many of the ideas proposed as
geoengineering solutions are still just ideas and need a lot more work to see if they are feasible. This is particularly
true of the solar radiation management ideas, many of which sound like something out of a really bad Hollywood B-
movie. These suggestions include changing the albedo of the Earth, i.e. increasing the amount of solar energy reflec-
