[pf] faulty logic (I think).

· I'm barely into creating (for the last half of August) :-

http://www.emucities.com.au/member/davd/GrNZ-RegionalRept-000831.html#top

 but I've just written-in a caption to one of 6 images, and am unhappy with
it:

"Biomass farms like this one in New York could serve two purposes: they
sequester carbon dioxide in vegetation and produce fuel for biomass power
plants."

· The caption came with the image, in one of the scores of reports put out
each half month by (in this case) the Lycos Environmental News Service (ENS).

· There's something wrong with the logic, at least of the implication, that
the "two purposes" are additive, i.e. that a biomass farm sequesters carbon
dioxide in vegetation, AND it produces fuel for biomass power plants.

· During stability (running normally), the biomass (i.e. wood-chip, bark
and leaves) fuelled power plant excretes X tons per day of carbon dioxide.
On average over the year, the biomass farm ingests the /same/ X tons per
day of carbon dioxide. Net result: the sun's energy, captured in the leaves
and deposited in the biomass, is fed into the power plant and comes out as
electric energy plus (quite a lot of) heat energy. Zero CO2 output from the
system.

· But there is no sequestering of carbon dioxide, as implied by the caption.

· Only during the 5 - 15 years while the biomass farm is in transition to
the stable state, i.e. the trees, hemp, or whatever are growing before
harvest, is there any draw-down of CO2 from the atmosphere. Even then,
/I/wouldn't call it sequestering - I'm only marginally willing to call
growing wood for wood-frame houses as sequestering {(1)there's a lot of
sawdust and other waste, and (2) the house's expected life of 50 - 75 years
is only just comparable with the maximum time by which we must have
finished our transition to living sustainably}.  Hardwood furniture does
sequester CO2, IMO.

· To restate my point: /Either/ you try to sequester CO2 by planting
long-lived (~100 year life-time) trees and letting them grow then fall over
from old age (i.e. they're not a crop), /or/ you use the
crop-plus-power-plant system to turn sunlight into electric energy. By the
way, the only sequestering is during the growth of the forest; at maturity
the CO2 released during rotting equals the CO2 deposited in the wood etc.
as the tree gets bigger and heavier. A mature forest can't /sequester/ more
CO2.

· You can't do both.  Am I right?

David.
(David MacClement) davd@ihug.co.nz 
http://www.emucities.com.au/member/davd/index.html#top
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