Tom and list:
1. I have no disagreement with any of your computations. The question of
“irreversibility” in the absence of CDR is well established. This note is to
add CDR to your analysis, and address your helpful "unless”. In addition to
your program, I have tried the following 50 year 100 ppm total in a simple
program at David Archer’s website. A paper by Boucher etal given in AR5,
chapter 12 talks of a very similar scenario. (Apologies for lack of citations
- I am in a rush today).
2. I hope we all agree that there is a Technical (not necessarily
Economic ) potential for CDR to achieve the (roughly) 400 Gt C removal (half
coming out of the ocean). Over 50 years this requires an average of 8 Gt C/yr
- very close to an annual 1% per year. We all know 8 Gt C/yr is huge, but few
would say that 1% change per year is huge.
3. Of course we have to also drop fossil resources and land use changes by
an even larger annual percentage, but renewables have been growing by a much
larger percentage annually. There is also a huge untapped potential for energy
efficiency (that can pay for the needed CDR). We also should consider (but I
haven’t) the externality costs of the fossil resources. I feel we will save
money by going to CDR. This is NOT a financially burdensome scenario I propose.
4. In my view of the needed 8Gt C/yr, I assign 2 to afforestation. so
(over 50 years) we add 100 Gt C to the roughly 500 Gt C of standing biomass. I
believe this number is assumed by Jim Hansen. I don’t believe he attributes
any thing new to the roughly 1500 Gt C of soil carbon (roots, microbes, fungi,
etc). I would add 100 Gt C there as well - now having gotten half way to the
needed 400 Gt C transfer of atmospheric and ocean carbon to the biosphere.
5. The 4 Gt C/yr remainder must come from 8 to 10 other CDR approaches.
My knowledge base is only in the biochar area, which I believe (hope I am wrong
- that there is a better) is the cheapest, so I will give only the biochar
argument. I make a similar (not the same) assumption as for afforestation -
that a tonne of C in char placed in soil will provide an additional tonne C of
out-yr sequestration benefits. Unlike the above argument for afforestation,
which only assumed new soil carbon, here I am assuming that but also a new
additional out-year above ground biomass C. So this is perhaps 1 Gt C added
above and below ground with an assumption of 2 Gt C/yr of directly-applied
biochar (by chance the same number as for afforestation).
6. The standard reference for biochar’s maximum future contribution is an
article by Wolff, Amonette, etal - with (at about 1 Gt C/yr) half of my needed
2 Gt C/yr total. They assumed there was no increase in out-year carbon
capture. They also stated that they had made only conservative assumptions;
they mostly used ag “wastes”. The contributions of woody biomass and
“plantations” were minimal. They assumed no perennial woody species
productivity improvement seen for the last century in ag species. Later
calculations by others of land use attributed land use for both ag and char
purposes to the char column alone. The most promising source of biomass and
land I have seen since their paper is agave and similar plants that capture CO2
mainly at night (and much higher water use efficiency) in the “CAM” (not C3
or C4) form of photosynthesis.
7. I recognize this is not proof of anything, but doubling a conservative
analysis leading to 1 Gt C/yr does not seem extreme. Authors such as Tim
Lenton and Johannes Lehmann have given annual sequestration biochar numbers
many times larger than my assumed placement of 2 Gt C/yr.
8. So now to address Tom W’s question of “cheap”. This is not the place
for a full dialog on that, but I think biochar purchase (or local production)
can be made for about $100/t char ($120/t C or $35/t CO2). If twice that, I
believe it would still be cheap enough. The reason for this optimism is that
biochar provides energy and soil improvement benefits that allow the char
production costs to be spread 3 ways - not only for sequestration. One can buy
char (produced badly and probably illegally) for as little as $100/t today in
some places.
9. Is there enough land? I say plenty given the land (2 Gha?) we have
ruined over the last several hundred years and arid land (3 Gha?) which the
“CAM” photosynthesis approach can hopefully turn productive. To get 2 Gt C/yr
from just 1 Gha of land requires only 2 t C/ha-yr (same as 200 gms C/sqm-yr).
Roughly half the carbon in biomass can be turned to char (much of the remainder
being available as carbon neutral energy to back up solar and wind). So we
need an NPP of only 0.4 kg C/sqm-yr (or 4 t C/ha-yr) - just about what we are
now doing in a global average sense (using 60 Gt C/yr/13 Gha). In many places
we do ten times better today.
10. I am not claiming great accuracy above - but if we double these numbers
then the annual average expenditures on the biochar side, would be $200/t C *
2 Gt C/yr = $400 billion per year - a small portion of today’s annual GDP of
$80 trillion. Appreciably less than the 1% of GDP one often reads for CDR -
and no-one is expecting global GDP to stay flat at $80 trillion.
11. I don’t believe a doubling for biochar sequestration subsidy cost is
appropriate, as we are beginning to see quite substantial (60% by one recent
corporate announcement) annual yield improvements for land receiving biochar
treatment. A few years earlier we talked of 10% average improvement. I trust
solid scientists to do even better when we truly understand how to make biochar
most effective. . The above numbers are also not taking account of numerous
other biochar financial benefits - possibly of equal societal magnitude
12. Where are the most inappropriate assumptions in the above? Is $200 or
$400 billion per year a bargain or out of the question?
Apologies for a rush response (that I tried hard to keep short).
Ron
On Oct 30, 2013, at 1:19 AM, Tom Wigley <wig...@ucar.edu> wrote:
> Dear all,
>
> Dropping CO2 concentrations to 350 ppm in 50 years is impossible
> unless we can find a cheap way to suck a whole lot of CO2 out of the
> atmosphere.
>
> Some simple calculations are attached.
>
> Tom.
>
> ++++++++++++++++++++++++++++++++++++=
>
> On 10/29/2013 2:18 PM, Ronal W. Larson wrote:
>> List and Brian:
>>
>> I just noted a mis-statement. See below.
>>
>>
>> On Oct 29, 2013, at 1:28 PM, Ronal W. Larson <rongretlar...@comcast.net
>> <mailto:rongretlar...@comcast.net>> wrote:
>>
>>> Brian (cc list) This to respond to your three inserts in my
>>> yesterday’s response to you
>>>
>>> BC1: */But that's not very good. Warming-induced feedback loops like
>>> methane deposits are already very scary. I don't say CO2 levels are
>>> irreversible; my point is about warming from all causes, and you need
>>> methods of cooling that are much quicker than 50 years. /*
>>>>
>>> *[RWL1: Brian’s “that” refers to my just previous statement (see
>>> below) that we could drop to 350 ppm in 50 years. Brian is NOT
>>> arguing for SRM here, although it may seem so. He is arguing for
>>> increased latent heat transfer - an approach that seems questionable
>>> at best - given the strong warming potential of increased atmospheric
>>> carbon.*
>>
>> RWL: The last word was supposed to be “moisture” - NOT “carbon”.
>> Apologies. I am too used to following “atmospheric” with “carbon”.
>>
>> Ron
>>
>> <snip remainder>
>>
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