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Soil carbon capture: Great loamy hope or bandaid?

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CleanTechncia

Recently on Quora I was challenged to assess the likely capacity of soil carbon sequestration approaches (sometimes referred to as biological carbon capture and sequestration or BCCS) by a researcher in the space. The premise was that two thirds of the carbon which had been sequestered in the soil had been lost into the atmosphere as grasslands were converted to large-scale agriculture, and that changing agricultural practices would be sufficient to act as a sink for the majority of excess CO2 emitted.

rsz_carbon_cycle

What exactly is the mechanism? How much potential does BCCS offer? How much effort would be required to implement a large scale fix? Reasonable questions, so I went hunting for answers.


How does BCCS work?

There have been some interesting findings in plant biology in the past two decades, specifically concerning something called glomalin.

Glomalin is a glycoprotein produced abundantly on hyphae and spores of arbuscular mycorrhizal (AM) fungi in soil and in roots. Glomalin was discovered in 1996 by Sara F. Wright, a scientist at the USDA Agricultural Research Service. The name comes from Glomales, an order of fungi.

To summarize the premise behind modern BCCS:

  • glomalin binds carbon better than previously understood
  • good soil management practices allow the fungi which produces glomalin to thrive
  • which allows more binding of carbon

Carbon has been lost from native soils as they became agriculturally productive. The concept of BCCS is shift to agricultural approaches which support glomalin from approaches which reduce it, increasing the carbon uptake of soil. The various sources provided  supported this theory (any sources not linked in the body of this article are provided below as additional reading).


How much carbon might be sequestered?

As a lot of the sources were Australian, I went to my go-to Australian source for good climate information, CSIRO. I found this very useful briefing paper on soil sequestration from 2010.

The part that leapt out at me in the Executive Summary of the material on p. iv:

Globally, this loss of SOC has resulted in the emission of at least 150 Petagrams (Pg) of carbon dioxide to the atmosphere (1 Petagram = 1 Gigatonne = 10^15 grams). Recapturing even a small fraction of these legacy emissions through improved land management would represent a significant greenhouse gas emissions reduction.

As CO2 has risen from 150 to 400 ppm, this represents an increase of about 1,170 gigatonnes of excess CO2 in total, and annually we are contributing about 10 gigatonnes.

Let’s make the assumption that all agricultural land globally could be returned to a baseline of the same sequestration as native land over the course of the next 50 years. That means that we’d be at about 1,222 gigatonnes of extra CO2 and the soil would sequester about 150 gigatonnes out of that total, or about 12%.

However, this 12% is dominantly a temporary biological sink.

That study showed that glomalin accounts for 27 percent of the carbon in soil and is a major component of soil organic matter. Nichols, Wright, and E. Kudjo Dzantor, a soil scientist at the University of Maryland-College Park, found that glomalin weighs 2 to 24 times more than humic acid, a product of decaying plants that up to now was thought to be the main contributor to soil carbon. But humic acid contributes only about 8 percent of the carbon. Another team recently used carbon dating to estimate that glomalin lasts 7 to 42 years, depending on conditions.

Glomalin, as with all biological sinks, is temporary. Movement of CO2 into permanent sinks occurs, but also movement back into the atmosphere. Biological sinks become saturated and then atmospheric levels of CO2 remain in balance with the sink.


Would it be sequestered fast enough?

There has been recent bad news for soil sequestration via a radiocarbon dating of soil carbon study published in Science by a UCal team in September 2016.

A gloss on the study in the Guardian is good and in more accessible terms.

Scientists from the University of California, Irvine (UCI) found that models used by the UN’s Intergovernmental Panel on Climate Change (IPCC) assume a much faster cycling of carbon through soils than is actually the case. Data taken from 157 soil samples taken from around the world show the average age of soil carbon is more than six times older than previously thought.

This means it will take hundreds or even thousands of years for soils to soak up large amounts of the extra CO2 pumped into the atmosphere by human activity – far too long to be relied upon as a way to help the world avoid dangerous global warming this century.

So the answer of 12% by 2050 is actually much slower, centuries slower in fact. That’s too slow to be of use in any near term attempt to deal with warming.


Does this mean BCCS will go away?

Like a more virtuous corn ethanol, BCCS enables governments to give money to farmers who are a large voting block. This is happening in jurisdictions around the world.

The science says it’s not a short-term climate solution, but that better tillage practices are a very good choice regardless. While sequestration might be a bit of a red herring, reduced soil erosion and better soil biology are strong net benefits regardless.


Is there good news out of this?

npp_change_bump_lrg-570x285Yes, actually.

Global green biomass has been increasing for the past 15 years or so as the rural poor move to cities and leave semi-arable land to go wild. In a tightly related story, we’re producing more food from less land under agriculture  globally.

The combination means that a great deal of land is returning to being a better carbon sink and that the area of land amenable to better practices is both smaller and under organizations more amenable to seeing it as a long term asset, agricorporations who are more likely to follow the science of better land management.


To be clear, improving land management practices to make the soil healthier and sustainable is something that’s excellent to do. It will help with long term ecosystem health and biosequestration. But it’s not a fix for our climate change problem this century or next. That will take electrifying everything, decarbonizing electricity and then cleaning up around the edges.

Source: CleanTechnica. Reproduced with permission.

  

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  • howardpatr

    “To be clear, improving land management practices to make the soil healthier and sustainable is something that’s excellent to do. It will help with long term ecosystem health and biosequestration. But it’s not a fix for our climate change problem this century or next. That will take electrifying everything, decarbonizing electricity and then cleaning up around the edges.

    That was known a long time ago by people working in related scientific areas BUT of course that did not stop Australia’s former, (and perhaps current), creationist PM(s) jumping onto the bandwagon as an excuse for doing nothing of any great consequence re anthropogenic climate change

    • Bungarra

      Should be part of the farming practice anyway!

  • Bungarra

    RE age of soil organic carbon. Depending on the situation, some of this carbon in is the form of charcoal which can be very long lived. Also, the sources for this such as partially burnt stubble, and also original vegetation depends on the history and m anagment of the site.

    Note that the use of partially burn wood etc was used to make the ‘Terra preta’ soils of South America. Should this be also used to use tree clipping / organic rubbish form urban sources? We would need to stop the real estate developers from converting some areas used for crops etc to houses and concrete.

    • Mark Roest

      Check out YouTube ‘Biochar in the Amazon’ — five-foot-thick beds of biochar lining the rivers, under the topsoil, and notice the mud dome that is put over the tree trunks when the survivors of the plagues let loose by the first European explorer show how they do it. That dome creates a low-oxygen atmosphere inside — in other words, it’s pyrolysis, or charcoal-making. Check out All Power Labs in Berkeley, CA for their pyrolysis refinery on a pallet — very advanced technology, and quite a low cost.
      If we divide up the tech jobs left after automation, and all grow our own food again (in 1900, over 90% of the population was farmers in the USA), and adopt Permaculture/arborculture and related approaches, and use that to support doing very high levels of biochar-making and burying, we can sequester geologic amounts of carbon for a thousand years. In the process, we will make our soils and crops much more resilient to climate disruption, as it stores water and nutrients in the pores, which are just the right size for plant rootlets to get in and absorb them in times of need.

      • Mark Roest

        And I forgot to mention that while I agree totally with 100% decarbonization of energy and transportation, and using new composites, Ultra-High-Performance-Concrete (UHPC), and structural geometries like the Bosch Captive Column (CaptiveColumn.com) to cut way back on the use of concrete (thus cutting its massive CO2 emissions), reducing livestock production of methane, and other ways to drastically reduce GHG emissions, we still need to restore the pH of the oceans, which have gone acid from sopping up excess CO2 from the atmosphere. Because of this, we need to do everything we can to pull CO2 back out of the atmosphere, so that it can have a lower CO2 partial pressure, and pull CO2 back out of the oceans, and restore the shell-forming and coral-forming species to health. That goal is worth getting every human being involved in one way or another, for lots of reasons you can find by searching.

  • Leigh Flitter

    (Australian) Peter Andrews should be essential reading for anyone concerned about this. His whole land/hydrology recovery method relies on more plants taking more carbon, and mulching it back into the soil to stop oxidation of existing carbon that has already made it there. His thrust is that it is the carbon in soil that is natural fertility for plants, and modern farming methods do not put it back. He then goes on to outline the principles of recovering land (and coolness) through the proof of what he had achieved on his property. Using the right plants, land is turned around to productive within 2 years – it carries better crops and 33% of the land remains green all year.
    He states that the lack of plants causes increase in *both* local heating, and local CO2 increase. Everyone else is barking up the wrong tree!

  • Brad Sherman

    When the Earth’s system was in balance without human interference, atmospheric CO2 was in that 200-300 ppm band and fossil fuels were sequestered. The increase in atmospheric CO2 concentration is less than the amount of CO2 emitted from FF combustion alone. We can measure FF combustion with much greater accuracy than we can estimate global soil C stocks.

    Soil C was only ever going to be a marginal contributor to changes in atmospheric CO2. I seem to recall that the Kyoto meeting only added land use change to the list of allowable mitigation approaches at the request of Robert Hill. The world wanted Australia to join the protocol but Australia didn’t want to accept the eventual loss of the coal industry so it lobbied for, and got, the whole land use change/soil carbon ‘get out of jail free’ card.

    One of the weaknesses of the older soil C models, and perhaps still a weakness in the CABLE model used by Australia, is that they never included any loss terms from the soil through groundwater transport. In the meantime, we aquatic scientists kept finding that our estimates of riverine transport of C was getting closer and closer to our estimates of net ecosystem production (the net amount of C fixed by terrestrial ecosystems). One interpretation of this result is that the overall global system was broadly in balance with substantial fractions of terrestrial sequestered C being returned to the ocean and atmosphere via our surface water bodies (lakes, rivers, and reservoirs).

    Soil C is a store, not a sink. It will fill up and assuming the soil C store returned to its, say pre -1800 value, there is still all that coal and oil that’s been burned up floating around in the atmosphere. I don’t think it is realistic to expect humanity to be able to cram more C into the soil over the entire earth than what was present before the industrial revolution.

    • That’s the idea behind different CCS approaches such as sequestering CO2 into wells underground or, even better, turning it into carbonate rock. It’s a better approach than soil sequestration in my opinion, although biochar has its merits.

      • Miles Harding

        The carbonate rock route does occur and is considered one of the stabilising influences on climate. The problem is that it takes millenia, while we are polluting over the scale of a few decades.

  • DJR96

    So it all boils down to putting a value on what is already being down. Using that value to trade and allow continuation of FF.

    Does absolutely zero to actually reduce emissions……..

  • Brian

    Biochar of wastes is far better. We harvest like we do now, use our harvest for food, clothing and lumber, then convert it to biochar, gas and liquid fuel. Biochar added to poor soils double productivity. Fossils use does far more harm than just emissions when burned. Extracting it is damaging, and we go to war for it. We waste out waste by paying to dump them which leaks methane into the air and toxics into the ground water. We no transport our waste long distance to dump them as well. No system is sustainable that does not reyclce our waste and reclaim the hydrocarbons and raw materials.

  • Robert Comerford

    Let us be honest here, soil carbon capture was nothing more than an accounting exercise to allow countries like Australia to continue to extract coal. We’ll promise not to develop land that was never going to be developed so that offsets our coal mining…. what is not to like in that scenario !!?