Table 3. An overview of the main ocean carbon cycle geo-engineering proposals, the concept behind these ideas and current status
of investigation.
Proposal Concept Status of research
Ocean fertilization Primary production in some areas of the ocean is lim- • Approximately 13 small scale in situ experiments have
ited by macro or micro nutrients (such as iron, silica, been conducted since 1993, but have proven incon-
phosphorus or nitrogen). By increasing the availability clusive about the CO
2
sequestration effectiveness of
of these nutrients, primary productivity could be in- ocean fertilization;
creased resulting in an acceleration of the natural rate • To make a viable contribution to reducing atmospher-
of CO
2
uptake by the oceans from 2 Gt C yr
–1
(Huese- ic CO
2
concentrations, ocean fertilization would have
mann, 2008) and increase CO
2
storage in the deep sea. to be carried out over large areas, and potentially
Any CO
2
stored in this way would be removed from the would need to be sustained on a millennial timescale
global carbon cycle for up to 1,000 years. (Lenton and Vaughan, 2009);
Promoted by commercial groups and enterprises (e.g. • International concern has been expressed, inter alia,
Climos) and with potential for trading credits on the about the high ecological risks. International bodies
voluntary carbon market. and experts have called for restrictions and caution
(e.g. IMO, 2007; CBD 2008; Gilbert et al., 2008; Sei-
bel and Walsh 2001);
• Parties to the London Convention agreed that, given
the present state of knowledge, ocean fertilization
activities other than legitimate scientific research
should not be allowed. An assessment framework for
future scientific research and in-situ experiments is
under development (IMO, 2008).
Altering ocean mixing Use of 200m long ocean pipes to enhance the mixing • Never reached field trial stage;
and upwelling of nutrient rich waters (e.g. Lovelock and • Calculations indicate sequestration flux that would be
Rapley, 2007); achieved is trivial on any meaningful timescale; and
Enhance downwelling by using floating pumps to costly (Lenton and Vaughan, 2009).
cool waters and form and thicken sea ice (Zhou and
Flynn, 2005)
Increasing ocean alka- Increasing the alkalinity of the oceans by: • This is as yet highly theoretical, but under active re-
linity • Adding carbonate, thereby increasing the capacity search, e.g. by Cquestrate, which is an opensource
of the water to absorb CO
2
(Kheshgi, 1995). Harvey project to explore the idea, encouraging evidence
(2008) suggested the use of finely ground limestone, based debate and investigation (Cquestrate, 2009);
other proposals foresee the use of thermally decom- • It is possible that the CO
2
emissions generated from
posed limestone (Cquestrate, 2009); preparing the carbonate material would match the
• Enhancing the solubility of CO
2
in the oceans by a pro- CO
2
sequestered (Lenton and Vaughan, 2009).
cess equivalent to the natural silicate weathering reac-
tion. HCl is electrochemically removed from the ocean
and neutralized through reaction with silicate rocks.
40
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