One year ago this month, I wrote for the first time about a highly controversial study, “Biomass Sustainability and Carbon Policy Study,” which was conducted by the Manomet Center for Conservation Sciences (MCCS). The Manomet study, as it is universally known now, has been used by environmentalists and coal companies alike as evidence in their fight to stop wood-to-electricity projects. Like nearly all of our public conversations these days, however, the most controversial parts of the study’s results were frequently (and often inaccurately) reported in the press, while the reasoned critiques of the study, which came later, were largely ignored.
Since the EPA is currently considering how it will approach applying the tailoring rule to bioenergy companies and other sources of biogenic CO2 (the comment period ended May 5), I thought it would be a good time to look at the arguments of those who have published critiques of the science underpinning the MCCS’ report.
But, first, a recap of the Manomet study’s conclusions. The study begins with the premise that the carbon cycle of a stand of trees begins when they are harvested and used as an energy source. Based on this premise, MCCS developed what it calls the “debt-then-dividend” framework. In keeping with this framework, the study argues that when biomass is burned, the carbon sequestered there is released into the atmosphere and that this creates a carbon “debt.” That debt is then repaid over the course of the next 30 (or more) years as the stand of trees regenerates. At some point, this new growth sequesters enough carbon to pay off the debt and then begins to pay carbon dividends.
The following figure, which we first shared with readers last year, is a hypothetical illustration of this framework. (Click on image to enlarge; hit back button to return to post.)
"Debt-then-Dividend Framework from the Manomet Center for Conservation Science study, "Biomass Sustainability and Carbon Policy Study"
It is this exact illustration that has been the focus of much of what has been written about the study—good and bad. The most recent critique of this scenario comes from Dr. William Strauss of FutureMetrics, who exposes “the fallacy that underpins the Manomet argument” in his article How Manomet Got It Backwards: Challenging the “Debt-then-Dividend” Axiom. The Manomet study’s logic begins with a stand of full grown trees. Trees sequester carbon as they grow from seeds or seedlings; as a result, Strauss argues, that is where the greenhouse gas accounting should begin. For instance, a stand of mature trees harvested in 2012 has been accruing a carbon dividend over the 30 (or more) year period it took for the tree to grow to maturity. When the trees mature, “we can then derive a benefit from that dividend by using those trees for energy,” says Strauss. Once the stand is replanted, it begins the cycle again, accruing carbon dividends as it grows and providing benefits once it is harvested. Figure 2 from Strauss’ paper illustrates his alternative framework. (Click to enlarge the image; use back button to return to post.)
"Dividend-then-Benefits Framework from Dr. William Strauss’ “How Manomet Got It Backwards: Challenging the “Debt-then-Dividend” Axiom"
Strauss’ framework—the “dividend-then-benefits” framework—seems the logical approach for analyzing the greenhouse gas impacts of woody biomass used for energy production, as it begins the analysis when trees start sequestering carbon. Using the “dividend-then-benefits” framework, the release of carbon into the atmosphere never exceeds the amount of carbon the same trees sequestered. According to Strauss, “if biomass is harvested from existing forests that will be sustainably managed in the future, there is no debt.” The process is carbon neutral. Compare that to the emissions of coal in Figure 2.
Jay O’Laughlin, Director of the College of Natural Resources Policy Analysis Group at the University of Idaho agrees with Strauss’ assessment. “Accounting for Greenhouse Gas Emissions from Wood Bioenergy” is O’Loughlin’s response to a call for comments from the EPA, which is currently considering how it will apply GHG emissions regulations to biomass combustion. According to O’Loughlin, Manomet’s decision to start the carbon clock ticking at the point when the tree dies is arbitrary. The study “stretches time like a rubber band from now into the future, but not from now into the past, as if the past does not matter. Given the continuous nature of the carbon cycle, this approach is not only arbitrary, but also makes the decisions about energy sources that are alternatives to fossil fuels more perplexing than they need to be. In addition, fossil fuels generate a debt that is never repaid nor expected to be repaid.”
The other major criticism of the Manomet report has to do with scale. The study assesses the carbon impact of a single stand of trees, not the entire forest system. In his article in The Forestry Source, “A Fatal Flaw in Manomet’s Biomass Study,” Alan Lucier writes the following: “The fatal flaw in this analysis is Manomet’s invalid assumption that modeling harvested stands in isolation is equivalent to modeling forests comprising a diverse population of stands.” By looking only at stands that are harvested and ignoring stands right next door that are not disturbed, Lucier argues, “the model creates a false impression that forest carbon stocks are always depleted from harvesting. . . . In real forests, changes in carbon stocks depend on rates of harvesting, growth, and mortality at larger spatial scales. . . . Carbon stock depletion on harvested stands is offset to some degree by carbon accumulation on stands that are not harvested.”
Strauss provides a clear example of this phenomenon: “f there is a forest system with 1 million tons of biomass on Jan. 1 of a given year and that system has 1.01 million tons of biomass on Dec. 31 of that same year then the forest has increased its carbon stock over the year and it is embodied in the extra 10,000 tons of biomass. If 10,000 tons are harvested from the system on Dec. 31, then the system begins the next year with the stock of biomass and carbon at the same level that it was at the beginning of the previous year.”
As Strauss says, “Manomet gets it backwards. There is no debt if the forest system has been in growth-to-harvest equilibrium or has a growth-to-harvest ratio greater than one and the forest is managed sustainably so that the net stock of biomass does not deplete.”
Based on Strauss’ work, and the work of other researchers who have called the results of the Manomet study into question, it seems logical to us that if we are performing an accounting of the greenhouse gas impact, we should start not at “today,” and focus on a single stand of trees, as the Manomet Center did, but at the beginning of the harvested stands life cycle and in context of the entire forest system. As Strauss says, “What happens “today” is not an isolated event unconnected with the past.” And what happens in one stand of trees in a forest is not an isolated event unconnected to the rest of the forest.
“Stand-level analysis is not capable of considering that harvests are scheduled over large areas and long time periods,” O’Loughlin points out. “In effect, other forest areas that have already been cut and are regrowing, as well as areas with established forests that will be cut in the future, help sustain resource supplies and maintain carbon balance in [a forest] at any given point in time.”
Given the overwhelming nature of the evidence supplied in the critiques of the Manomet study, evidence based in environmental science and not political science, it seems clear that those who insist that carbon accounting should begin at the moment trees are harvested instead of the moment they begin sequestering carbon are latching onto the “debt-then-dividend” framework because it suits their own purposes, like the Stop Spewing Carbon Campaign run by Margaret Sheehan in Massachusetts (see story).
To those people, I quote Lucier’s compelling conclusion:
Manomet’s study does not change the reality that sustainable forest management is an effective strategy for controlling greenhouse gas emissions (GHG). The GHG benefits of sustainable forest management are associated with forest regrowth after harvest; lower risk of wildfire; production of energy-efficient materials and biomass energy; and carbon sequestration in forests and wood products. Forest protection can also provide GHG benefits, but it is generally less effective than sustainable forest management over the long term. As noted by the Intergovernmental Panel on Climate Change, “In the long term, a sustainable forest management strategy aimed at maintaining or increasing forest carbon stocks, while producing an annual sustained yield of timber, fiber or energy from the forest, will generate the largest sustained mitigation benefit.”
Of course the carbon impacts of biomass power have to be assessed using the current emissions and current atmospheric CO2 level as a starting point. The fact is that burning anything emits CO2, and resequestering that CO2 takes decades. It’s absurd to assume otherwise - it doesn’t make physical sense.
Manomet answered Strauss and the rest of the “I just can’t accept that time runs forward” crowd at http://www.manomet.org/node/322
so the usfs needs to get off their duffs an plant more trees,especially in old burns, .
Respectfully, I must disagree with even your first two words: it is not “of course.” The “physical” science you gloss over (calling something “absurd” is hardly a convincing argument) is far from decided on the starting point.
Even if I accepted your points, however, I would still not come to the same conclusions you do. Why? Because I take a long-term, comparative view of electricity sources. Why? Because it is short-term thinking and the refusal to acknowledge that there will never be a single solution to our energy and environmental problems that have gotten us to the point we are currently facing.
Point 1: “Decades” is better than never. Fossil fuels will never reabsorb atmospheric carbon. Trees always will.
Point 2: If we start today, we still need to include in the equation that forests grow and sequester more carbon every day. So, if we start today, we need to not only count how much carbon is emitted by using forest biomass to produce electricity, but we must also count how much carbon is sequestered every day going forward. Time runs forward on both accounts. After a few years (if burning logging slash) or a a decade (if using pulpwood-sized trees—the only whole trees used in energy production), that carbon will be reabsorbed through regrowth, and we’d be even. From there, as long forest growth is equal to or exceeds harvests, the carbon equation would be in balance. It is this type of long-term thinking that will help us solve our energy problems (see article on Long-Term Energy Policy). Opposition to this approach—at least until wind and solar can be relied on for baseload power—only guarantees that we’ll burn more coal and oil. The life cycle GHG emissions from biomass are monumentally better (see post).
[...] in climate mitigation, pockets of disagreement have gained traction in the US (read a related post: Dividend then Benefit). A recent comprehensive review of research on the life cycle carbon accounting for wood published [...]
The Great Slayer of biomass in Massachusetts, attorney Meg Sheehan- it turns out her family’s multi million dollar foundation is heavily invested in fossil fuels: http://www.farmfieldforest.org/2011/05/environmental-wolf-in-sheeps-clothing.html
[...] Dividend then Benefit, Not Debt then Dividend [...]