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MRV in Woody Biomass Storage

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Acronyms!  I’m absolutely sick of acronyms!  Every time I turn around there is another acronym.

GWP?  TRL?  TEA?  LCA?  CBP?  WBS?  TSB?  The list goes on.  Over time they become more familiar, but, we should all remember:  Knowing a Three Letter Acronym (TLA) when another person does not, is not a badge of honor.  It IS an opportunity to carefully communicate a foundational climate science principle, and to build a wider understanding of what we are all up to.

Chief among the TLA’s in climate is MRV, or “Measurement, Reporting, and Verification”.  It has gained importance and significance as new methods of Carbon Dioxide Removal (CDR is another TLA) have come to the fore.  MRV is also increasingly important because the legitimacy of existing forms of CDR have been called into question.  If you haven’t heard of MRV, you probably will soon.

Different CDR methods require different tactics and strategies, because the various methodologies rely on different production processes and different scientific principles.  You have to understand the important components of MRV for the CDR methodology you are studying.

Woody Biomass Burial (WBS), my particular area of interest, is no exception.  Certain activities and processes must be measured and reported in order to strengthen public understanding of its effectivenss.  How?  The measurements can be assembled in equations that quantify the effectiveness of WBS CDR.

So, in Woody Biomass Storage, what do we measure, report, and verify?  Here is a partial list, along with some quick commentary.  In future, we’ll dig into greater detail on some of these.

Woodstock measurement is important, and is either measured on the CDR site, in a lab, or both.  This type of measurement generally occurs upfront, before woody biomass is actually buried.

  • Tonnes of wood is the core measurement for articulating how much carbon is sequestered.
  • Moisture content of wood is relevant because sequestering the water in the wood does not generally fight climate change, and in fact can cause more rapid decomposition.
  • Carbon Content of wood measures the mass of carbon atoms in wood as a percent of overall mass, and usually hovers around 50%.  
  • Lignin Content in the wood is carefully measured, with the higher proportion generally better.  This is because lignin functions like a preservative, keeping the wood protected from microbial agents and reducing the rate of decomposition
  • Carbon to Lignin ratio should be low.  High lignin content relative to carbon content.  Means more lignin available to keep the carbon in the wood rather than decomposing.

Operations are an important MRV consideration because the “carbon cost” of the operations themselves reduce the net benefit of Woody Biomass Storage.  Worse, operations tend to occur right up front, which maximizes the Global Warming Potential of those operations.  As such, a key objective is to minimize operational carbon cost, especially upfront.  In WBS, operational carbon cost generally comes from three activities: 

  • Forestry Activity, in which waste wood is thinned from forests.  Other terms for this process is “fuels reduction” or “liability biomass removal.”  Carbon may be emitted as chainsaws using internal combustion engines are deployed.  On the upside, chainsaws are steadily being replaced by battery-powered saws, leading to the likely reduction in “carbon costs” from this activity in the future.
  • Transportation Activity, in which wastewood is moved from the location where it is cut, to the woodcache, or burial site.  In Woody Biomass Storage it is important that these sites are close together (At Woodcache our goal is less than 30 miles), and this is one reason why WBS is well-served with thousands of medium-sized sites around the world, rather than one big site.  Fortunately electrification of heavy trucks is likely in coming years, reducing the carbon intensity of transportation activity.
  • Excavation Activity, in which earth is excavated, woody biomass placed in the hole, and earth replaced in a carefully engineered manner.  This activity is today conducted by heavy diesel-powered equipment, but within the next decade it is likely to be replaced by electrical equipment.  

Conditions in and around the burial pit are important because these help slow wood decomposition.  As such, monitoring and ensuring a set of conditions leads to better Carbon Dioxide Removal.  These conditions include:

  • Coolness, which can slow down or even stop aerobic and anaerobic microbial activity.  At Woodcache we tend to bury deeper in order to maintain cooler temperatures, and have deployed subterranean temperature sensors to measure our success.  
  • Dryness, which also inhibits microbial activity.  In addition to ensuring we bury dry wood, we also carefully engineer runoff and have deployed an evapo-transpirative layer designed to allow moisture to escape.  We have also deployed subterranean moisture monitors to measure soil and wood dryness. 
  • Anoxic Environment which is intended to keep oxygen away from the wood.  With zero oxygen, aerobic microbes die, forcing anaerobic microbes into play.  In our current projects at Woodcache we seek an oxygen-deprived environment, but not oxygen-free, which allows us to reduce the risk of methane production, a more dangerous greenhouse gas than CO2 in the near term.  The exact oxygen strategy will vary by pit as we scale around the world. 

Results are the headliners when it comes to MRV.  For WBS the most important measures are:

  • Proportion of greenhouse gases emerging from the woodcache.  Since methane is more dangerous than carbon dioxide in the near term, it is important that the proportion of carbon dioxide is high, and the proportion of methane is low.  We run flux chamber experiments to answer this question. 
  • Quantity of greenhouse gases emerging from the pit.  Woody Biomass Storage is based on the idea of slowing down carbon emissions dramatically rather than completely stopping it.  We run flux chamber experiments to understand this rate and aggregate the experiments over time to determine the long-term rate of wood decomposition.
  • Cap Conversion Effectiveness measures the soil’s capacity on the surface to capture any methane rising out of the earth, and destroy it, replacing it with carbon dioxide.  We measure this effectiveness by contrasting relative concentrations of the two gases underground, and contrasting it with relative concentrations above ground.

That’s a lot to measure!  It may seem excessive, but the effort is well worth it on the way to public confidence in WBS, and CDR writ large.  

Let’s not despair.  We can blunt the ravages of climate change.  CDR and WBS are meaningful parts of the solution.

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