Part 2. Exploring Scientific Evidence and
Evaluating Choices
Section 7: Advanced details on the "Iron
Solution"
How much iron?
Christopher Anderson, writing in the 15 November 1990 issue of Nature (Vol 348, p. 188), summarizes the discussion of the Iron Solution at a US National Research Council conference in Irvine, CA. John Martin had calculated that 300,000 metric tons (300 million kg) of iron added to ocean water around Antarctica would remove 2 billion metric tons of carbon from the atmosphere in the form of carbon dioxide. For comparison, the annual global release of carbon as carbon dioxide by burning of fossil fuels is about 6 billion metric tons.Anderson reports that revised calculations presented at the conference suggested that the amount of iron needed is more like 1 to 5 million metric tons and only 1 billion metric tons of carbon in the form of carbon dioxide would be captured and used by the algae.
An expert from DuPont Corporation estimated that iron in the form of liquid ferrous chloride would cost about $600 per metric ton of iron. Five million metric tons would then cost $3 billion for the estimated capture of 1 billion metric tons of carbon or 3.7 billion metric tons of carbon dioxide. The indicated cost of the ferrous chloride presumes that it is rather inexpensive because it is an industrial waste byproduct. If it had to be produced in such large quantities, the cost likely would be higher. Costs to transport the caustic chemical to Antarctica were not calculated, but estimated to be much higher than the cost of the material.
Conference participants also raised the issue of environmental impact of the abrupt increase in algae growth in the region. Small crustaceans, known as krill, feed on the algae and likely would benefit from increased food availability. However, the krill lay their eggs just below the surface. Krill eggs and decaying algae both slowly sink. The decay process acting on the abundant algae depletes the oxygen supply of the surrounding water, possibly creating an oxygen-starved environment for the newly hatching krill. Furthermore, tunicata, which are jellyfish-like organisms that eat both krill and algae, could experience a population explosion and upset the current ecological balance of the region.
Anderson concludes his conference summary with a consensus view by participants that the Iron Solution is a scientifically interesting proposal that merits further investigation through controlled laboratory and field studies.
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