Hello Dr. Larson,
Thank you for your interest in my research. To answer your questions:
“a) that only as much carbon can be removed from the atmosphere as was
inserted (no explanation on why this limit), and”
This evidently was not clear enough in the paper but there is no limit to
how much carbon is removed from the atmosphere using CDR. The model is
prescribed the atmospheric CO2 concentration at a given date and diagnoses
net human emissions from the carbon cycle. The totals for removal are seen
in table 1. In all cases more carbon needed to be removed that had
originally been emitted to the atmosphere to return atmospheric CO2 to 280
ppm.
"b) is to be taken out as a “mirror” of the way it was inserted (and
I am not understanding details of the mirror, but this seems highly
unrealistic), and"
The mirror is an intentional simplification. There are off course an
infinite number of possible pathways to remove CO2. The path actually
taken would likely depend on technology, desirable cooling rate, and the
industrial capacity of a possibly damaged and impoverished civilization. I
selected mirrored scenarios because they are simple but less idealized
than either instant removal of CO2 or linear removal of CO2.
"c) requires going back to 280 ppm (not the usual 350 ppm)"
I initially did conduct unpublished model runs where I returned
atmospheric CO2 concentration to 350 ppm. However, I found the models to
difficult to evaluate as the climate was never in equilibrium with 350
ppm. To evaluate the differences between the final climate and the
Holocene climate I needed to use the pre-industrial climate as a known
baseline. Also note that in the simulations that where published the
Greenland ice sheet does not restabilize until 280 ppm is reached
(although this could be a hysteretic effect).
" d) looking at very high out year peaks, that are inconsistent with
the concept of CDR."
I do not see how high peaks are inconsistent with the concept of CDR. CDR
is a technology that can be deployed at whatever time that society deems
that it needs to be deployed (and the society has the resources to deploy
the technology).
Note also that the new IPCC scenarios the Representative Concentration
Pathways prescribe concentration pathways not emissions pathways. It is
possible the follow any of the RCPs while deploying technology to capture
a significant fraction of anthropogenic emissions. One could for example
remove emissions such that an emission total that would otherwise lead to
RCP 8.5 instead lead to RCP 6.0.
“ b) Use annual removals that emphasize speed and are reasonably least
cost - not a “mirror” of anything.”
One must also consider the induced rate of atmospheric cooling. Much of
the damage from climate change comes from the “change”. Agriculture and
ecosystems will need time to readapt to the cooled climate.
“So, I hope that Dr. MacDougall or others will extend his analyses in
these directions.”
At present I do not have any plans to continue research in this area. In
fact this paper evolved from a side projected focused on “can we fix this”
that was never approved by my committee. However, a graduate student
supervised by Dr. Karen Zickfeld of Simon Fraser University is working on
a similar project (with the same ESM) but focusing of economic modelling
of negative emission scenarios.
Once again thank you for your interest in my work and good luck developing
biochar tech.
P.S. It is Mr. MacDougall.
Sincerely:
-Andrew MacDougall, MSc
PhD Candidate
University of Victoria
Victoria BC Canada
> Andrew and list
>
> 1. I have been meaning to comment on this article by Dr. Andrew
> MacDougall, that you cited in October. I was reminded by it being
> referenced in the last Science issue (Dec. 6, p 1149) I received. The
> article is NOT behind a paywall. It is at:
> http://onlinelibrary.wiley.com/store/10.1002/2013GL057467/asset/grl51021.pdf?v=1&t=hp8v0lqy&s=27b2334b807e010482b6e4fa3f41a8703797473f
>
> 2. I took the main result to be quite negative for CDR. But there
> still some positives to gain from an analysis I believe can be improved.
> The faults I find are only in the papers four scenarios, which are:
>
> a) that only as much carbon can be removed from the atmosphere as was
> inserted (no explanation on why this limit), and
>
> b) is to be taken out as a “mirror” of the way it was inserted (and
> I am not understanding details of the mirror, but this seems highly
> unrealistic), and
>
> c) requires going back to 280 ppm (not the usual 350 ppm)
>
> d) looking at very high out year peaks, that are inconsistent with
> the concept of CDR.
>
> 3. I am of course unhappy that there is nothing about biochar in this
> article (for out-of-date reasons), but the specifics of the CDR approach
> are not critical and are not I believe in the model. There are a number
> of useful references to somewhat similar papers. There is no sense of
> “Irreversibility”.
>
> So I am still hoping to see modeling as detailed as in this paper, that
> includes the potential for more soil carbon. There are some out year
> freebies with biochar that have not been modeled by any group, to my
> knowledge. To the best of my knowledge none of the removed CO2 ends up
> in soil.
>
> The model is better than many by including Arctic methane release.
> The long time periods to reach the year-1850 conditions are because of
> the four faults I am claiming above in the four assumed scenarios.
> These should be readily fixable.
>
> 4. The positives that I think we can take from the article relate to
> what can happen with more realistic scenarios, which should have these
> four features, that replace the above #2 assumptions:
>
> a) No limitations on the amounts that can eventually be removed from
> the atmosphere.
> (The required removal amounts are a very small percentage of
> CO2 in the oceans, or allowed deep underground - and I know
> of no reason that soil carbon couldn’t be doubled or tripled
> without harm.)
>
> b) Use annual removals that emphasize speed and are reasonably least
> cost - not a “mirror” of anything.
> (For biochar options, the limiting speed at first will be the
> manufacture of pyrolysis hardware - which presumably could
> have a doubling time at first measured in months. For sure,
> the output of such factories will not be time-independent, so
> the growth rate should not be linear. When a production
> plateau will be reached is a function of costs and benefits,
> which can be controlled by policy decisions ($10 or $100/tonne
> CO2, etc). This can be handled parametrically, with numbers
> like 1, 10 or more Gt C/yr being assumed and costed. The
> important point is that for decades I think we can assume an
> annual increase in removal, not the annual decrease that (I
> think) is in the MacDougall model. I would hope for a model
> that talks of getting to 350 ppm well before 2100.
>
> c) First investigate the 350 ppm end point; continue to 280 ppm as
> a second stage effort.
> (350 ppm just because there has been so much emphasis on that
> number. 280 ppm should certainly be modeled as well.)
>
> d) I would restrict attention at first only to the two lowest of the
> new IPCC AR5 peak scenarios. I believe his present analyses already
> adequately argue against the two higher.
>
>
> 5. So, I hope that Dr. MacDougall or others will extend his analyses in
> these directions. The cause of CDR can be enhanced by trying to achieve
> what some climate scientists are saying we need to do - or showing why it
> cannot be. Lower ultimate costs will result by striving for speed and
> avoiding terms like “the year 3000” (in the abstract).
> To repeat, I am not intending to be critical of this paper. I
> believe the results are reasonably correct for the assumed scenario. I
> am suggesting we need also to look at scenarios that are much less
> restrictive.
>
> Ron
>
>
> On Oct 8, 2013, at 3:18 AM, Andrew Lockley <[email protected]>
> wrote:
>
>> http://onlinelibrary.wiley.com/doi/10.1002/2013GL057467/abstract
>>
>> Reversing climate warming by artificial atmospheric carbon-dioxide
>> removal: can a Holocene-like climate be restored?
>>
>> Andrew. H. MacDougall
>>
>> DOI: 10.1002/2013GL057467
>>
>> Geophysical Research Letters
>>
>> Keywords:
>>
>> Holocene;Climate warming;Reversibility
>>
>> Abstract
>>
>> Most climate modelling studies of future climate have focused on the
>> affects of carbon emissions in the present century or the long-term fate
>> of anthropogenically emitted carbon. However, after carbon emissions
>> cease there may be a desire to return to a “safe" CO2 concentration
>> within this millennium. Realistically this implies artificially removing
>> CO 2 from the atmosphere. In this study experiments are conducted using
>> the University of Victoria Earth system climate model forced with
>> novelfuture scenarios to explore the reversibility of climate warming as
>> a response to a gradual return to pre-industrial radiative forcing. Due
>> to hysteresis in the permafrost carbon pool the quantity of carbon that
>> must be removed from the atmosphere is larger than the quantity that was
>> originally emitted (115–180% of original emissions). In all the
>> reversibility simulations with a moderate climate sensitivity a climate
>> resembling that of the Holocene can be restored by 3000 CE.
>>
>>
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