I would like to invite comments on biological carbon sequestration
focused on the "accounting" acpect of it. In particular, estimates
for production and collection of biomass suitable for sequestration
purposes from land (150 M sq.km) and/or oceans (360 M sq. km). As an
example, say we want to use pelagic algae as feedstock, primary
productivity is ~1t C per sq.km. per annum, we collect that, do
pyrolysis, sink charcoal, sell oil, and use gaseous product to power
our floating plant. Charcoal accounts for ~50% of carbon, so we'll
sequester ~1.8 Mt C for every 1% ocean surface we cover. It ain't
enough, by far. Benthic algae harvests are ~1,000 times better (per
sq.km), so it would be ~1.8Gt C for every 1% coverage - seems really
attractive, untill you recall that there ain't much area suitable to
grow benthic algae.
Besides, this all assumes that we don't add any carbon back to the
athmosphere in the process. For the example above, if algae are
helped by artificial fertilization, such as with Lovelock-type
upwelling pumps, this assumption may be incorrect (because the
nutrient-rich water brought up by artificial upwelling may outgas more
CO2 than the resultant algae bloom sequesters). Other factors include
fuel/energy use during production/collection/disposal etc.
I think putting estimates together in this format, both for land-based
and for ocean-based primary production, could be a very useful for
comparing different options. Naturally, the more comprehensive such a
review is, the more useful it could be.
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