Hiya Ellis,
First let me say that I may have used the term geo-sequestration too loosely. I was referring to this type of biogeo-sequestration; enhancing the planet's natural systems to utilize more CO2. Keeping it stored is trickier, but possible.
The point is that if we can sequester as much as possible now, later when emissions have finally been lowered, it would be tolerable to have those carbon stores cycle back into the atmosphere. I'm also certain that at least some of the planet's natural systems have been degraded so as to no longer have net carbon storage. Restoring these systems would help now, and also allow us to offset emissions in the future.
Currently, with diminished global net carbon storage (if not a net release), and with emissions only increasing (however slowly), only global-scale sequestration will make any appreciable change in CO2 levels.
I didn't realize Nature has an article on this subject:
Lehmann, J., A Handful of Carbon, Nature 447:143 (May 10, 2007).
I need to read yet, but here's a quote:
"Biochar has been shown to improve the structure and fertility of soils, thereby improving biomass production[3]. Biochar not only enhances the retention[6] and therefore efficiency of fertilizers but may, by the same mechanism, also decrease fertilizer run-off."
Same is true for water/soil moisture & it increases microbial diversity.
...an interesting sounding article in the April 30, 2007 issue of Discover by Micheal Tenneson titled "Black Gold of the Amazon", which highlighted the importance of biochar to the ecosystem. "Some crops have been cultivated on the same plots for 40 years without ever needing fertilizer."
also sounding good, but I haven't checked yet:
Lehman, J., 2007 Bio-energy in the black. Frontiers in Ecology and the Environment
Lehman, J., Gaunt, J., and Rondon, M.: 2006, "Biochar sequestration in terrestrial ecosystems - a - review", Mitigation and Adaptation Strategies for Global Change 11, 403-427
btw, there is a some actual geo-sequestering (i.e. pumping CO2 underground to enhance oil recovery; some mining/land use).
~SA
