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Climate Hustle

Soil Carbon in the Australian Political Debate (Part 1 of 2)

Posted on 15 August 2011 by alan_marshall


At 27.3 tonnes [i], Australia's annual per capita emissions of greenhouse gases (CO2 equivalent) are the highest among the Organisation for Economic Co-operation and Development (OECD) nations. Along with Canada, Australia also combines a large land area with a low population density. This provides scope for the nation to achieve a portion of its CO2 abatement through agricultural sequestration.

While forestry is the most obvious and easily calculated carbon sink, it is the sequestration of CO2 in agricultural soils that has received particular attention in the current political debate about our national response to climate change. While it is more expensive, and less secure, than forestry, it has the advantage of allowing the land to continue to be used for crops or pasture.

The Biology of Soil Carbon

Carbon stored in soil includes both short lived crop residues and long lived humus. The latter is of particular significance to the current debate on soil carbon transience, as it cannot be lost from soil during droughts or fires. Humus is a gel-like substance fixed in the soil by mycorrhizal fungi, which obtain dissolved organic carbon from the roots of plants. Once carbon is sequestered as humus it has high resistance to microbial and oxidative decomposition. A more detailed explanation of these processes can be found in the submission of Dr. Christine Jones to the 2009 Inquiry into Soil Sequestration in Victoria [ii].

In crop lands, soil carbon is increased through adopting no-till or minimal till practices. In pasture lands, it is increased by introducing bio-diverse ground cover, and controlling grazing. In both crop and pasture lands it can be increased by application of biological agents, but at some increased cost.

Kyoto Compliance and Permanence

Article 3.4 of the Kyoto Protocol refers to carbon sequestered through land use other than forestry. It includes pasture, woody vegetation less than 2 metres high, and soil carbon. Its rules cover movement of CO2 both into the soil through photosynthesis, and out of the soil through oxidation. Australia has not yet signed up to this article out of concern about potential carbon loss through drought and bushfires, though the Government is attempting to renegotiate the rules. For carbon credits to hold their value, the CO2 must be permanently removed from the atmosphere. That means there must be no change to land usage that would diminish soil carbon. This creates difficulties in selling affected land, which would be subject to a covenant to protect the stored carbon. Without factoring in the cost of such responsibilities, the voluntary carbon offset market in the Australia and the US understate the true cost of this means of sequestration. Perhaps mindful of this, Dr. Michael Robinson at the Australian Government Healthy Soils Symposium, commented on the cost implications as follows:

Verification costs make soil carbon trading untenable with carbon prices as they are. Most schemes define permanence as 70 to 100 years. A contract will stipulate that carbon must be sequestered for that time period. [iii]

Readers will point that CO2 stays in the atmosphere for centuries, but 100 years may at least give us time to find other solutions. In my view the impact on the sale price of land under covenant depends on the reward for CO2 abatement. Under a low carbon price, the sale price of covenanted land could be significantly discounted unless the soil carbon industry as a whole is profitable enough to maintain or increase the value of all rural land. Permanence also requires periodic testing and verification, with associated costs.

Cost Estimates

On page 40 of Dr. Jones' submission, she refers to the scheme in Portugal, compliant with Kyoto Article 3.4, which aims to permanently sequester 0.91 million tonnes of CO2 in 42,000 hectares of soil. That equates to 21.7 tonnes per hectare. Dr. Jones states the cost of the scheme is $13.8 million, which works out at about $15.20 per tonne. According to the International Monetary Fund figures for 2010 [iv], per-capita income in Australia is more than 70% higher than in Portugal. Therefore, if we adjust the return to farmers in Portugal to reflect the higher per-capita income in Australia, the result is about $26 per tonne.

I now move on to the report of the Inquiry into Soil Sequestration in Victoria [v], which I expect was made after assessing submissions from Dr. Jones and others. In section 6.3.2, the report quotes a study conducted by the International Energy Agency by Australian and US scientists. A key finding of this study was that a price of $50 per tonne of CO2 would be required to persuade landholders to devote sufficient land to achieve 31% of the potential abatement:

In the zone covering the Gippsland region, the economic potential of adopting no-till practices is 31% of the theoretical potential at a carbon price of $50 per tonne, which increases to 87% at a carbon price of $200 per tonne. The average costs of adopting no-till practices to sequester carbon in south eastern Australia were lower than the average costs of adopting minimum till practices.

Another cost indicator comes from the Australian Farm Institute, which has estimated the cost of building up soil carbon, through changed management and fertilizer application, at "somewhere above $30 a tonne." [vi]

A Realistic Price for Soil Carbon

The above sources give us a realistic range of the cost of sequestering CO2 in the most suitable soils of $26 to $50 per tonne. For these soils, my estimate is $35 per tonne (in less suitable soils, or a poorly designed regulatory environment, the cost would be significantly higher). This estimate allows $15 per tonne of CO2 for fixing the carbon in the soil, and a minimum $20 per tonne to keep it there for 100 years. If we use $35 per tonne as a working estimate, we find such a price to be competitive with the premium required to generate electricity from wind, and cheaper than the premium for solar-thermal.

On my website, Climate Change Answers, I compare the relative costs of various methods of sequestering carbon and various methods of generating renewable energy. In the move to a low carbon economy, both solutions will both be needed. Very low cost opportunities for abatement are limited, so it is time for our society to accept the reality that, however the transition is managed, there is going to be a cost.

Note that the above costs are denominated in Australian dollars, in line with the source documents. During the last year, the Australian dollar has risen above parity to the US currency. To compensate for this, I suggest you think of the above costs as denominated in current US dollars.

Political Implications

In Australia, both sides of politics have included soil carbon in their policy mix to respond to the challenge of climate change. However, the Opposition has gone out on a risky limb in its heavy dependence on this solution. In the second part of this post, to be published later this week, I will look at the implications of the cost of soil carbon on the climate change policies of both major parties.


[i] Climate Analysis Indicators Tool, Version 8.0, World Resources Institute, 2010
[ii] Dr Christine Jones, Submission to the Environment and Natural Resources Committee Inquiry into Soil Sequestration in Victoria
[iii] As reported by Australian Government Grains Research and Development Coorporation, Ground Cover Issue 70 - September - October 2007
[iv] International Monetary Fund, data from World Economic Outlook Database - April 2011
[v] Parliament of Victoria Environment and Natural Resources Committee, Inquiry into Soil Carbon Sequestration in Victoria, September 2010
[vi] The Australian of 16 August 2010

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Comments 1 to 11:

  1. The whole natural sequestration seems to me to be full of dubious propositions.

    Sequestration by forestry is one because as far as I can tell a mature forest should have respiration and photosynthesis in balance and therefore no sequestration can occur.

    The article of course emphasizes humus but I missed any figure for it's actual soil lifetime. A few years ago I buried a large amount of plant matter in the garden and within a year the soil had reverted to clay. I attributed this to the activity of worms. So I am guessing the lifetime of humus is 1 to 5 years. Therefore to maintain humus-based soil carbon would take constant I tensive soil management. i imagine you would get no increase in carbon past the first 1 to 5 years of management.

    Feel free to provide better figures.
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  2. One crazy idea I had was that soil carbon could be increased by forestry slow burns. As long as the temperature was not hot enough to oxidize the soil and the charcoal yield was high, the sequestration rate would be high and cumulative over time as the process was repeated.

    Charcoal of course is very resistant to oxidation when buried and so the sequestration time scales should be very long.
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  3. I'm afraid that LazyTeenager is correct. Though Soil Sequestration in an option, certain people have massively overstated its benefits, usually as a means of overlooking the obvious-namely reduction of our use of fossil fuels!
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  4. LazyTeenager. If you look at the archeology of terra preta soils you'll see that if manures and other nutrients are combined with charcoal, the structure and carbon content can be retained for millennia.

    Without using charcoal or biochar, you may not get much more than a century or so. Seeing as farmers are committed to improving their soils on decade/generation timescales, this isn't much of a problem. They already spend bulk money on their current land management practices. It's really a matter of finding ways to make a different regime of land management maintain profitability. (Fertility is not the main issue because higher humus soils are almost automatically more fertile.)

    The central problem is that this issue has been ignored for such a long time. The research is likely to be playing catch-up (or leap-frog) with implementation for quite a while.

    The eternal issue in farms and forestry is continuation of good practice when land is sold. Every farming community has horror stories of how a 'beautiful' property was absolutely wrecked by a new owner (or the next generation) overgrazing or denuding vegetation or drying up a creek by their incompetent management.

    I think it will eventually become a bit like windfarms. A small annual payment for increasing and maintaining carbon values - by some agreed formula for measurement.

    That word 'agree' will likely ensure that the policy won't be easy or quick to implement.
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  5. LazyTeenager @1

    Mature forest is of course in equilibrium as far as the carbon cycle is concerned. It is important to preserve them as stores of carbon, but as you point out, sequestration only occurs in growing forests. In Australia, much of our eucalypt forest has been logged, so the secondary growth is a potential carbon sink. Eucalypts are fast growing, and include some of the tallest species of trees on Earth. So there is plenty of "upside". As far as the economics is concerned, my source is "The Cost-Effectiveness of Carbon Sequestration in Harvested and Unharvested Eucalyptus Plantations" by A. J. Richardson. On my website, I have published a cost comparison of carbon sequestration options. I have been a little more conservative than Richardson, estimating the cost of the unharvested eucalypt plantation option at $20 per tonne of CO2. That makes it cheaper than soil carbon, but the land cannot be used for other agricultural purposes.

    Your other point is also well made. It is estimated that between 70% and 90% of the carbon in crop residue is returned to the atmosphere within a few years, therefore involving minimal sequestration. That is why my post focuses on the gel-like humus, which degrades much more slowly, returning just 2% of stored carbon back to the atmosphere per year. (Forgive me, I am still searching for the scientific paper in which I recently read these figures.) Where land use switches to no-till practices, carbon levels will increase to a point where the fresh humus created each year is in equilibrium with that which is lost.
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  6. adelady @1, lazyteenager @2

    You are both right in recognising the virtues of charcoal / biochar, of which I am a big fan. It would be worthy of a separate post. The reason I have focused on soil carbon is its prominence in the current political debate in Australia.

    The first and greatest virtue of biochar for sequestration purposes is its stability. That automatically leads on to its second virtue, which is the ease with which the stored carbon can be accounted. The third virtue is the quantity that can be stored on a given area of land, and the fourth virtue, which it shares with soil carbon, is its enhancement of fertility. Indeed, the terra preta soils in the Amazon Basin cover great swathes of land, and suggest that the fertility of that area once allowed it to sustain a much higher population.

    Biochar is a stable form of charcoal produced from heating natural organic materials (crop and other waste, woodchips, manure) in a high temperature, low oxygen process known as pyrolysis. Click here for fact sheet. The by-products of the process are the gases carbon monoxide and hydrogen, which together can be synthesised into bio-fuel. It is not easy to get consistent figures for the cost of production of biochar. My estimate of $65 per tonne is based on the price of agricultural charcoal, offset for the value of bio-fuel. If anyone has a more reliable figure, please let me know.

    The potential of biochar was recognised and promoted by Australia’s previous leader of the opposition, Malcolm Turnbull. However, interest in the technology has been quietly dropped by the current opposition leader, who is not prepared to put serious money into mitigation.
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  7. Marcus @3

    I agree that the CO2 emissions from burning fossil fuels vastly exceed that which can readily be sequestered by agricultural means. However, with the CO2 at 393ppm and rising, we are on a trajectory that will take us into the “red zone” within a few decades. A growing number of voices, such as Bill McKibbin’s are calling for the world to adopt a more ambitious target of 350 ppm. We are in an “overshoot” scenario. If we are ever to return to a safe level, we will need to sequester the excess CO2 now in the atmosphere.

    I want to thank you all for your feedback. Your comments have been thoughtful. Take another look on Thursday, when Part 2, looking at the political implications, will be posted.
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  8. You all may be interested in an email exchange I had with Greg Hunt, the opposition spokesman on this stuff. Depressingly light on detail – what did I expect? But here are a couple of quotes:

    "We expect that the cost of buying back abatement will average $12 per tonne. We have allowed $15. And in the first year to ensure a fast start we have allocated enough to purchase 20[0] million tones at the conservative allowance or 215 million tonnes at our expected average cost."

    Then this, in response to my question about what they were actually intending to purchase:
    "A farmer could capture carbon in their soil, capture carbon in trees or in revegetation. A council could clean up their waste landfill gas or we could provide incentives to clean up a power station by converting from coal to gas …"

    Don’t know how much of that you get for $13 a tonne …
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  9. Matt Holden @8

    Along with Malcolm Turnbull, Greg Hunt is one of the few members of the Opposition to accept climate science. I praise them both for defending it. As climate action spokesman, Hunt’s task is not easy. After Tony Abbot overturned the Opposition’s previous bipartisan support for an emissions trading scheme, he had the unenviable job of stitching together a politically plausible alternative with inadequate funding. Hence the emphasis on soil carbon offsets, which Hunt believes he can acquire cheaply. I believe he has seriously underestimated the cost of the permanent sequestration of CO2 in agricultural soils, something I will explain in detail in Part 2. In the meantime, you might be interested that in his written response to me, Hunt stated:

    I would also note that soil carbon has traded at $1 per tonne in the United States.

    If Hunt thinks this figure means anything, he is sadly out of touch. He is quoting the US voluntary market, which has no fixed rules, and therefore nothing on which to fix a value. The Republicans, ideological allies of our Opposition, blocked Obama’s attempt to put a price on carbon. As a consequence, the voluntary market collapsed. The credits sold at $1 per tonne were dumped on the market at a fraction of their cost of production.
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  10. How nice to read a description of what soil carbon refers to. Having read the oppositions document titled 'Direct Action' there was no description of what the method entailed. There was no suggestion as to how farmers or whoever would be paid for the capture of carbon, presumably other than by some form of extra tax - perhaps a carbon tax?
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  11. I, too, am an Australian and also an engineer, but offer no opinion about the costs of soil C-sequestration.
    But the article re-uses the sophistry that "Australia's annual per capita emissions of greenhouse gases are the highest among the OECD..."
    Why not try thinking laterally? Why not emissions per square kilometre of land, or forest? [I know the answer; the figure permits no alarmist conclusion; based on emissions per skm of land, Australia is right down near the bottom, along with Scandinavia; same applies to emissions /skm of forest]
    If you calculate emissions per dollar of GNP, you will get a more meaningful figure. For Australia is a big commodity producer and exporter. If this country produced only enough food and raw materials for its own needs, it could cut its total emissions by a third [also wiping out half its export income] Reverting to a reduced agrarian and simple mining economy would also remove another portion of the emissions (even as it kills off the aluminum and steel industries). But this would not reduce demand for manufactured goods, as long as the populace can afford to import them.
    You may increase population and total emissions even when emissions per capita fall. Yet, up till yesterday, I had heard nothing either from government or opposition about a population plan for Australia. To run a scare campaign against emissions while allowing unlimited growth is absurd.
    Current ridiculous public policy claims we can cut back coal combustion without closing coal mines. Oops! How does that go?
    Adding hypocrisy to confusion, the government turns a blind eye to coal and gas exports. "Tighten your belt, but don't let it stop you exporting at full tilt" is the incredible sophistry being advanced by the rulers - as if fuel burned outside the borders is irrelevant to the debate.
    Former PM Rudd's Kyoto- prot endorsement never mentioned Australia's preeminent coal exporting role. Ah, you see, it all hangs on a slender thread: the chimera of 'clean coal'. Clean coal has become a talisman to wave at critics and skeptics. Nobody is certain how 'clean coal' will ultimately materialise, though it must- somehow - resolve all these contradictions and solve all problems. But, just where do you buy it?
    Making the electricity generation industry bear the brunt of emissions reduction will prove unworkable. So a biological sequestration proposition has some future.
    In that vein belongs a piece of CSIRO research published about 2005. Its authors came to some quite interesting conclusions. It appears that vegetation- biomass- in Australia has increased, perhaps doubled in amount, since initial European settlement. The CSIRO paper explains this by enhanced atmospheric CO2 levels, particularly during the 20th century. Higher CO2 levels promote plant growth and also make plants more drought-resistant.
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