Fwd: [geo] Radiocarbon constraints imply reduced carbon uptake by soils during the 21st century

[Ronal W. Larson]

Tom and Soil-Age list

I agree with your several messages today on this Science article.  But let me urge taking this article as also a “plug” for biochar - as you have done.  I send this only because there are some added cites below (just sent to a different list) that get at soil carbon - and intentional anthropogenic means of building it up.

I wouldn’t be too hard on modelers - this is one huge complex problem and soil carbon benefit is only one of many items needing more effort (such as not predicting arctic ice disappearance at all well).  Soil carbon modeling is just as difficult and just as important.  The modelers need our support in doing better.  I am amazed at how many soil-model articles are out there that could be used to advance biochar.

Ron

Begin forwarded message:

From: "Ronal W. Larson" <rongre...@comcast.net>

Subject: Re: [geo] Radiocarbon constraints imply reduced carbon uptake by soils during the 21st century

Date: September 24, 2016 at 3:05:24 PM MDT

To: Geoengineering <geoengi...@googlegroups.com>

Cc: Andrew Lockley <andrew....@gmail.com>

List, cc Andrew

I would like to advance an opposite view - that this article is giving soil CDR (through biochar) a boost.   Biochar is not the only form of “soil CDR”, but it is the only one with claims to recalcitrance (older soil carbon).  My guess is that of the 157 sites which the authors looked at with age distributions, a high percentage of those with older carbon were so blessed because of wildfires and charcoal.  

The paper itself seems (to a non-expert) well done - but I found the supplemental even more interesting.  I was surprised especially that the CESM model (C for Community - the first of five) shows such a small amount of existing soil carbon (at least in the main soil carbon category being analyzed) - much less than the other four.   I have been in contact with the developers of the CESM model - but not yet convinced them of the difference in biochar from other means of accomplishing the French goal from COP21:  “4p1000”.   The supplemental (probably free) is at: 

http://science.sciencemag.org/content/suppl/2016/09/21/353.6306.1416.DC1

There are a wonderful set of papers given in the cites.  The one that looked most pertinent to this article was supposed (via Google Scholar) to be at this site - but wasn’t:  http://escholarship.org/uc/item/1pw7g2r2#page-1.   It leads instead to a non-fee paper with this title: Explicitly representing soil microbial processes in Earth system models” .  That is pertinent, but is anyone able to get the desired paper in non-fee form?

The Science paper (and all the cites I investigated) ignored biochar.  It would be most interesting to have these ESM (= Earth System Models) authors investigate biochar in a similar age-of-carbon manner.  Starting with the age, composition, and high NPP of the Amazon’s extensive Terra Preta soils should be worthwhile in answering questions about the validity of biochar as a soil-CDR approach.

Ron

On Sep 22, 2016, at 5:58 PM, Andrew Lockley <andrew....@gmail.com> wrote:

Poster's note : appears to imply that rather more care needs to be taken with soil, and that soil CDR will be significantly more challenging than is sometimes argued.

http://science.sciencemag.org/lookup/doi/10.1126/science.aad4273

Radiocarbon constraints imply reduced carbon uptake by soils during the 21st century

Yujie He1,*, Susan E. Trumbore2, Margaret S. Torn3,Jennifer W. Harden4,5, Lydia J. S. Vaughn3, Steven D. Allison1,6, James T. Randerson1

Email: yuji...@uci.edu

Science  23 Sep 2016:
Vol. 353, Issue 6306, pp. 1419-1424
DOI: 10.1126/science.aad4273

Abstract

Soil is the largest terrestrial carbon reservoir and may influence the sign and magnitude of carbon cycle–climate feedbacks. Many Earth system models (ESMs) estimate a significant soil carbon sink by 2100, yet the underlying carbon dynamics determining this response have not been systematically tested against observations. We used14C data from 157 globally distributed soil profiles sampled to 1-meter depth to show that ESMs underestimated the mean age of soil carbon by a factor of more than six (430 ± 50 years versus 3100 ± 1800 years). Consequently, ESMs overestimated the carbon sequestration potential of soils by a factor of nearly two (40 ± 27%). These inconsistencies suggest that ESMs must better represent carbon stabilization processes and the turnover time of slow and passive reservoirs when simulating future atmospheric carbon dioxide dynamics

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