Andrew,
Ocean Macroalgal Afforestation is more of a concept revival with better technology and increased urgency than a new idea. The paper is vetted by co-author David Chynoweth, who has decades of research on seaweed to energy. I confess to also being a co-author.
You hit the key question: At what scale do demand limitations kick-in?
First note that demand (not sustainability) is limiting because the ecosystem scales beyond 9% of the world ocean surface with environmental benefits defined by increased biodiversity and primary productivity. Unlike most biomass-to-energy or BECCS, Ocean Afforestation is not limited by nutrient recycling at any steady-state situation. (No free-lunch. OMA is solar powered.)
In the paper, and the six supplements, we limited the extent of Ocean Afforestation to 9% of ocean surface because that area corresponds to a reasonable estimate of total world fossil energy demand in 2030. It seems reasonable that the demand for bio-methane is the demand limitation because the process is funded primarily from biomethane sales.
---------- Original Message --------
Subject: [geo] Negative carbon via Ocean Afforestation
From: Andrew Lockley <andrew.lock...@gmail.com>
Date: Tue, January 08, 2013 8:37 am
To: geoengineering <geoengineering@googlegroups.com>
Poster's note: From the abstract this sounds pretty breathless to me.
I imagine that the economics of scaling will be complex, particularly
when demand limitations kick in, and transport costs are properly
factored.
http://www.sciencedirect.com/science/article/pii/S0957582012001206
Negative carbon via Ocean Afforestation
Antoine de Ramon N‘Yeurta et al
http://dx.doi.org/10.1016/j.psep.2012.10.008
Abstract
Ocean Afforestation, more precisely Ocean Macroalgal Afforestation
(OMA), has the potential to reduce atmospheric carbon dioxide
concentrations through expanding natural populations of macroalgae,
which absorb carbon dioxide, then are harvested to produce biomethane
and biocarbon dioxide via anaerobic digestion. The plant nutrients
remaining after digestion are recycled to expand the algal forest and
increase fish populations. A mass balance has been calculated from
known data and applied to produce a life cycle assessment and economic
analysis. This analysis shows the potential of Ocean Afforestation to
produce 12 billion tons per year of biomethane while storing 19
billion tons of CO2 per year directly from biogas production, plus up
to 34 billion tons per year from carbon capture of the biomethane
combustion exhaust. These rates are based on macro-algae forests
covering 9% of the world's ocean surface, which could produce
sufficient biomethane to replace all of today's needs in fossil fuel
energy, while removing 53 billion tons of CO2 per year from the
atmosphere, restoring pre-industrial levels. This amount of biomass
could also increase sustainable fish production to potentially provide
200 kg/yr/person for 10 billion people. Additional benefits are
reduction in ocean acidification and increased ocean primary
productivity and biodiversity.
Highlights
► Ocean Afforestation concentrates carbon dioxide for storage.
► Ocean Afforestation also produces biofuels, food, and biodiversity.
► Plant nutrient recycling might sustain the ecosystem to <350 ppm
carbon dioxide.
► Multiple products reduce the cost of sequestering carbon dioxide.
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