Sunday, September 21, 2008

Biochar - Atmospheric CO2 "Mitigation".

This posting follows my last on biochar and the likelihood of it being used as a long-term form in which to store carbon captured from the atmosphere. In a nutshell (no pun intended), plants absorb CO2 through photosynthesis, are harvested and then pyrolysed to yield this relatively stable form of carbon along with a release of energy and other useful liquid and gaseous products, some of which might also be used to furnish fuels. To be practical, the process must produce more energy overall than it consumes. The biochar is tilled into soil which can improve its fertility, crop yield, fertilizer requirements and water-retention abilities. Thus, many pressing issues are addressed in a single action, in respect to global warming, phosphate and water shortages, and the difficulty in growing enough food to feed the burgeoning world population and alleviating poverty in the developing world. Put in such terms biochar begins to sound little short of a miracle.

Humans emit around 7 billion tonnes of carbon into the atmosphere annually from burning fossil fuels, and so that amount must be absorbed in addition to remediating the levels of CO2 that are already there. In rough numbers, if theories about anthropogenic global warming are correct, it would be a reasonable aim to deplete the amount of CO2 in the atmosphere to pre-industrial levels, or say a drop from 380 to 280 parts per million (ppm), or 100 ppm. The mass of the atmosphere is 5.3 x 10^15 tonnes (less than one millionth the total mass of the Earth), and thus it contains:

(44/30) x (12/44) x 100 x 10^-6 x 5.3 x 10^15 = 2.12 x 10^11 tonnes, or 212 Gt of carbon. In this sum, 30 is asumed to be the average molecular mass of an "air" molecule, 12 is the atomic mass of carbon and 44 the molecular mass of CO2.

Over a 40 year period (so that we have accomplished out feat by 2050, the magic year when all governmental targets are to be met), we thus need to remove 212 + (40 x 7) = 492 Gt of carbon, which works out to 12.3 Gt per year.

If we assume a mean crop-mass of 30 tonnes per hectare per year of which 40% is carbon based on a carbohydrate formula of C6H12O6, this amounts to 0.4 x 30 = 12 tonnes of carbon per hectare per year, and so we would need (12.3/12) x 10^9 ha = 1.02 x 10^7 km^2, i.e. around 10 million square kilometres of land to grow it on. This can be compared with 150 million km^2 for the total land mass of the earth, of which around 15 million km^2 is arable and around another 30 million is pasture land. There are swathes of existing forest (including rainforests) but we don't really want to begin cutting them down, since they are principal carbon-sinks, although growing trees e.g. sycamore etc. as part of a managed sustainable programme (harvesting them at regular intervals) might make a substantial contribution to the total carbon-capture volume.

Not all of the arable crops can be converted to biochar, of course, but manure etc. might be from the animals and humans that eat them. Probably, to achieve the aim of capturing almost 500 Gt of carbon over 40 years would require working close to the limits of the planet's growing capacity, and a concomitantly vast investment in engineering, along with policy, commercial, social and all other aspects in an integrated programme. Like many other postulated sustainable technologies, biochar too may fail the crucial "Scale Test" in the final feasibility analysis.

Finally, what would be the depth of biochar generated by the capture of 492 Gt of biochar (essentially carbon)?

If we assume a density for carbon of 1 tonne/m^3, that gives a volume of 492 x 10^9 m^3 for its biochar. If we use that same land area of 1.02 x 10^7 km^2 = 1.02 x 10^13 m^2, we have a thickness of:

492 x 10^9 m^3/1.02 x 10^13 m^2 = 0.048 m = 4.8 cm,

or a mere sprinkling of around two inches!


Professor Chris Rhodes said...

Hi Erich!

I am also a fan of biochar since as you say it addresses many issues of CO2, NOx, soil fertility, using less phosphate fertilizer and indeed water!

I went to an excellent conference about it in Newcastle a couple of weeks ago, and it does seem to be the only strategy that begins to grapple with all the above.

I don't belivee there is some wonder technology just round the corner e.g. hydrogen that is going to save us and so working eith the natural world in this way seekms apt!

I agree that to get this one rolling - and it is a big beast - will take a lot of cooperation between governments, industry and indeed all activities.

Keep coming back!



Unknown said...

Chris, Good to see you finally blogging about biochar! I think we need to be more realistic on the scalability issue. If we can follow Jim Hansen's recommendation and keep CO2 levels under 350ppm by the end of this century to avoid climatic tipping points, this may be achievable, maybe within as little as 50 years. See . It would take an enormous, coordinated effort, and be dependent on eliminating coal-driven CO2 emissions, presumably with CCS, but this level of scalability seems potentially doable. Continuing down this path may eventually see carbon dioxide levels return toward pre-industrial levels, but this is less important than avoiding passing a point of no return in regards to ice sheet stability.

Mark Breiter
CarbonZero Foundation

Erich J. Knight said...

This is the first biochar product I've seen in the market. The Carbon Charcoal Group's Carbon-Based Soil Amendment (CSA), in on going plot trial at VT,

Nitrogen Management and the Effects of Compost Tea on Organic Irish
Potato and Sweet Corn

"Subplots (two beds, 23 m long) were in-row placement of Soil Biology
Innovations granules at planting—control (no CSA) and CSA applied at
22-33 kg/ha (30#/Acre) (see Irish potato and sweet corn sections for
different rates applied). CSA is a proprietary product , composed of dehydrated compost tea absorbed on

This study only states compost tea amended char, but I am told by the
maker of CSA that root analysis MYC rates are high. The VT study
got a 20% increased yield in corn with this very low application rate of 20# / acre.
Given say 150 bushels / acre , add 20% = 30 bushels @ $5 /bushel = $150, and the $70 cost for 20# seems justified given it's spread at planting in the seed drill's dry boxes.

Charcoal Green is a Biochar (Bio-Charcoal) management tool that rejuvenates the biodiversity of soils and replaces the essentials organisms that were lost. When the right set of organisms are present and performing their functions both plant health and profitability soar.


Professor Chris Rhodes said...

Thanks Erich,

I am guessing we will see more commercialization of biochar from now on.



Professor Chris Rhodes said...

Hi Mark,

good to meet you in Newcastle recently and good too that you are still reading my musings here!

Yes, I am as usual emphasising "scale" and I agree that some values less than I have here to restore pre-industrial CO2 concentrations could have a considerable effect.

I agreee also that the scale reains large, as is true of all putatuve new technologies to deal with the energy/CO2 problems facing humankind.

Indeed we need to make a clear decision on a global basis of which to go for, and then act concertedly to achieve them.

However, actions on a local scale multiplied by the huge world population could add-up to a massive overall influence.



Erich J. Knight said...

Total CO2 Equivalence:
Once a commercial bagged soil amendment product, every suburban household can do it,
The label can tell them of their contribution, a 40# bag = 150# CO2 = 160 bags / year to cover my personal CO2 emissions. ( 20,000 #/yr , 1/2 Average )

But that is just the Carbon!
I have yet to find a total CO2 equivalent number taking consideration against some average field N2O & CH4 emissions. The New Zealand work shows 10X reductions.If biochar proves to be effective at reducing nutrient run-off from agricultural soils, then there will accordingly be a reduction in downstream N2O emissions.

This ACS study implicates soil structure as main connection to N2O soil emissions;

biochar papers at the ACS Huston meeting see Ron Larson's post

Biochar Studies at ACS Huston meeting;



665 - III.


Most all this work corroborates char soil dynamics we have seen so far . The soil GHG emissions work showing increased CO2 , also speculates that this CO2 has to get through the hungry plants above before becoming a GHG.
The SOM, MYC& Microbes, N2O (soil structure), CH4 , nutrient holding , Nitrogen shock, humic compound conditioning, absorbing of herbicides all pretty much what we expected to hear.

4 MYC mechanisms ?
Why the Massive Fungi growth?
4 mycorrhizae(MYC)mechanisms;
These mechanisms are (in decreasing order of currently available evidence supporting them): (a) alteration of soil physico-chemical properties; (b) indirect effects on mycorrhizae through effects on other soil microbes; (c) plant–fungus signaling interference and detoxification of allelochemicals on biochar; and (d) provision of refugia from fungal grazers. We provide a roadmap for research aimed at testing these mechanistic hypotheses.

My Terra Preta Prayer

Our Carbon who art in heaven,
Hallowed be thy name
By kingdom come, thy will be done, IN the Earth to make it Heaven.
It will give us each day our daily bread and forgive us our atmospheric trespasses
As we forgive those Kyoto protocols that trespass against Soil Sequestration
And lead us not into fossil fuel temptation, but diliver us from it's evil
low as we walk through the valley of the shadow of Global Warming,
I will feel no evil, your Bio-fuels and fertile microbes will comfort me,
For thine is the fungal kingdom,
and the microbe power,
and the Sequestration Glory,
For ever and ever (well at least 2000 years)


Professor Chris Rhodes said...

Nice one, Erich!

I am a poet too, as I have sprinkled in this blog from time to time!

Should we rename it from "Terra Preta" to "Terra Maravillosa"? or "Terra Estupenda"?!