cbd-ts-66-en

Part I: Impacts of Climate-related Geoengineering on Biological Diversity
forcing required to counteract anthropogenic climate change. In part this likelihood of very low effectiveness is
due to the very large volume of the ocean (1.3 billion km3): substantive changes to the carbonate chemistry of a
significant proportion of that volume need to be made to have any drawdown effect on atmospheric CO2.
Impacts of local excess alkalinity on marine biodiversity
While the theoretical chemistry of the processes of enhancing ocean alkalinity is relatively straightforward, the
impacts on those processes on biodiversity (if the technique were to be deployed) are much more uncertain.
In particular, the biological effects of temporarily enhanced Ca2 + ions and dissolved inorganic carbon are not
adequately known.
It could be expected that the initial local spatial and temporal pH spike might be harmful to biodiversity (and
hence, potentially, ecosystems and their services). However, this impact is transient and could be minimized
through rapid dilution and dispersion and, in the case of particulate material, by controlling the dissolution rate
of the substance through its particle size.
There are large unknowns associated with enhanced ocean alkalinity, due to limited knowledge of effects on
atmospheric CO2 and potential biological impacts. In particular, no field experiments have been carried out, and
there are a limited number of theoretical papers available. Furthermore, as already noted, it is questionable whether
any of the approaches above can be scaled-up sufficiently to make a difference to the global carbon budget in a
cost-effective way. Nevertheless, local use of enhanced alkalinity techniques may provide a means of counteracting
the worst effects of ocean acidification for specific high-value marine ecosystems, e.g. coral reefs.
5.4.2 Land-based enhanced weathering
Closely similar to the techniques discussed above, it has been proposed that the natural process of land-based
weathering could be artificially accelerated; for example, by reacting silicate rocks with CO2 to form carbonates,
bicarbonates and other products. One proposed method is to spread finely-ground silicate minerals such as olivine
over agricultural soils and river catchments.318 It has been estimated that this approach could globally sequester
up to 1 Gt C yr-1, using at least 3–4 Gt yr-1 of olivine (for comparison, current coal production is ~6 Gt yr-1).
The method would be most effective in the humid tropics. If the Amazon and Congo basins could both be fully
treated with olivine at an application rate of ~300 g m2 yr-1, their combined carbon sequestration potential has
been calculated319 as 0.6 Gt C yr-1. However, river pH would estimated to rise to 8.2 (currently 5.7–7.8) and the
additional delivery of biologically-available silicon could increase the regional-scale abundance of diatoms in the
ocean. The latter effect could potentially increase atmospheric CO2 drawdown through ocean fertilization effects.320
No field studies have been published to date to quantify CO2 uptake rates by land-based enhanced weathering,
although direct measurements of chemical changes, with associated carbon uptake, have been made for magnesium
carbonate minerals in mine waste.321
Impacts on biodiversity
The addition of alkaline rock dust, e.g. olivine, to low pH, nutrient-deficient soils may (under certain conditions)
increase the productivity of those soils, thereby reducing the incentive to convert previously non-agricultural
land into agricultural land. However, positive impacts cannot be assumed for all soil types, and, in order to have a
significant effect on the Earth’s climate, large-scale mining, processing and transport activities would necessarily be
318 Schuiling & Krijgsman (2006).
319 Köhler et al. (2010).
320 Oral presentation by Peter Köhler at Planet under Pressure conference, London, 27 March 2012.
321 Wilson et al. (2009).
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