I must admit that I am getting skeptical when I hear numbers in that
order of magnitude:
The total net primary production in the oceans presently is about 50 Gt
carbon, and 80% of that is converted back into inorganic carbon (and
nutrients) by heterotrophs before it gets a chance to sink out from the
sunlit upper layer of the ocean. The roughly 10 Gt carbon (some newer
works even estimate just 6 Gt carbon) that sink out have to be balanced
by the upward mixing of nutrients (and a little bit by atmospheric
deposition of bioavailable nitrogen and phosphorus) in the Redfield
ratio of about 106:16:1 of C:N:P.
So, if you want to remove 20 Gt carbon per year from the atmosphere,
you'd have to increase the nutrient supply to the total surface ocean by
a factor of three, maybe four. Maybe I am a bit too pessimistic here,
because there are species like Sargassum which have a higher C:N:P ratio
than the average phytoplankton, so you get somewhat more carbon per
nitrogen/phosphorus. But even if it is just doubling, I can't imagine
that you can sustain such a nutrient consumption by fertilizing from
outside the ocean (especially since phosphorus is scarce already now),
you'd have to tap into the inorganic nutrients stored in the deep ocean.
How long can you do that?
If we assume that we harvest all the 20 Gt carbon in algae from these
factories and do something durable with them (to minimize lossed through
heterotrophy and problems with creating oxygen minimum zones), we
effectively remove nitrogen/phosphorus from the ocean. How much is that
per year?
Let us for simplicity assume Redfield ratios, I grant errors by a factor
of two or so. 20 Gt carbon then corresponds to (20
g/12(g/mol)/6.625(molC/molN))*1.0e15 or about 2.5e14 mol nitrogen. The
ocean has a volume of 1.33e18 m^3, and the average concentration of
available nitrogen (mostly nitrate) is 30 micromol/L or mmol/m^3
(calculated from the world ocean atlas), most of that is in the deep
ocean. This gives a total inventory of 4.0e16 mol nitrogen. 2.5e14
mol/year is thus more than half of a percent of the total available
nitrogen in the world oceans, which means you could try that for about
150 years, then everything is gone At that pace, nitrogen fixers are
unlikely to resupply the loss (nowaday, the residence time of nitrogen
is roughly 5000 years), and they can do that only for nitrogen, not for
phosphorus anyway. Letting technological problems aside (like: How do
you move 2.5% of the total nitrogen in the world oceans evry year up to
an area 2% of the ocean surface) I would call the whole idea - at least
that the scale suggested - a prime example of an unsustainable process.
Best regards,
Christoph Voelker
On 07.09.17 23:37, 'Robert Tulip' via geoengineering wrote:
The assumption behind the NYT interactive model
<https://www.nytimes.com/interactive/2017/08/29/opinion/climate-change-carbon-budget.html?action=click&pgtype=Homepage&clickSource=story-heading&module=opinion-c-col-right-region®ion=opinion-c-col-right-region&WT.nav=opinion-c-col-right-region>
that the upper bound for carbon removal is 12 GT CO2 by 2080 is too
slow and small. We should think five times as much and five times as
fast.
Immediate aggressive investment to build industrial algae factories at
sea could remove twenty gigatons of carbon (50 GT CO2) from the air
per year by 2030, using 2% of the ocean surface, funded by use of the
produced algae.
That would stabilise the climate and enable no change in emission
trajectories, a policy result that would satisfy both the needs of the
climate and the traditional economy.
Robert Tulip
------------------------------------------------------------------------
*From:* Eric Durbrow <[email protected]>
*To:* geoengineering <[email protected]>
*Sent:* Thursday, 7 September 2017, 3:13
*Subject:* [geo] Carbon budget/removal in NYTimes interactive
FYI There is a slick interactive graphic at the NYTimes that lets
people see if they can meet the world’s carbon budget restriction but
a combination of reduced emissions AND achieving Carbon Removal.
At
https://www.nytimes.com/interactive/2017/08/29/opinion/climate-change-carbon-budget.html?action=click&pgtype=Homepage&clickSource=story-heading&module=opinion-c-col-right-region®ion=opinion-c-col-right-region&WT.nav=opinion-c-col-right-region
I failed after clicking on Reduce in all geographic areas and Achieve
in Carbon Removal.
--
You received this message because you are subscribed to the Google
Groups "geoengineering" group.
To unsubscribe from this group and stop receiving emails from it, send
an email to [email protected]
<mailto:[email protected]>.
To post to this group, send email to [email protected]
<mailto:[email protected]>.
Visit this group at https://groups.google.com/group/geoengineering.
For more options, visit https://groups.google.com/d/optout.
--
You received this message because you are subscribed to the Google
Groups "geoengineering" group.
To unsubscribe from this group and stop receiving emails from it, send
an email to [email protected]
<mailto:[email protected]>.
To post to this group, send email to [email protected]
<mailto:[email protected]>.
Visit this group at https://groups.google.com/group/geoengineering.
For more options, visit https://groups.google.com/d/optout.
--
Christoph Voelker
Alfred Wegener Institute for Polar and Marine Research
Am Handelshafen 12
27570 Bremerhaven, Germany
e: [email protected]
t: +49 471 4831 1848
--
You received this message because you are subscribed to the Google Groups
"geoengineering" group.
To unsubscribe from this group and stop receiving emails from it, send an email
to [email protected].
To post to this group, send email to [email protected].
Visit this group at https://groups.google.com/group/geoengineering.
For more options, visit https://groups.google.com/d/optout.
