Stephen Mulkey, PhD
15 October 2016
The Gainesville Renewable Energy Center, a woody biomass power plant that uses waste wood near Gainesville, Florida
“Well planned sustainable biomass power plants are a viable source of clean renewable electricity, and this is helpful for the task of phasing out coal-fired power plants. Knee-jerk opposition to all biomass projects has no sound scientific basis and is harmful to attempts to stabilize climate for the sake of our children, grandchildren, and future generations.” — James Hansen, Climate Science Awareness and Solutions Program, Earth Institute, Columbia University
In the summer of 2013, a close relative of mine called me at my office in Unity, Maine, breaking more than a decade of no direct communication. I was surprised, and I asked my administrative assistant if Ted (not his real name) was sober. She said that she thought so, and I took the call. Ted had struggled throughout his adult life with an addiction to alcohol, but indeed, he sounded sober and seemed just to want to chat. We talked about current events and my job as a college president. I asked him if he had quit drinking, and he said, “Yeah, my doc told me that it was killing me.” I congratulated him, but he quickly added, “I just drink beer now. No more whiskey.” Ted died a few months later from multiple organ failures caused by his drinking.
Many alcoholics try what Dr. Robert Smith, a co-founder of Alcoholics Anonymous, called “The Beer Experiment” and they all soon discover that switching to a less concentrated form of ethanol maintains the addiction and leads to even more drinking. Stockpiling the basement with cases of Bud Light merely services the addict’s essential requirement for booze. Such a substitution is analogous to switching from coal to wood as a fuel, a less concentrated form of energy, which results in even more carbon pollution than burning the coal necessary to generate the same amount of electricity.
The addiction metaphor has frequently been applied to our seeming inability to stop using fossil fuels. Like the alcoholic who switches from whiskey to beer, replacing coal and oil with woody biomass at first seems like it would serve to put less CO2 into the air because trees take up carbon through photosynthesis. In fact, the European Union officially treats woody biomass as a renewable form of carbon neutral fuel for power generation. With good intentions, many regions of the US have sought to reduce their carbon footprint by turning to woody biomass as a fuel source. The rationale for this stems from the fact that the carbon gained through photosynthesis to produce the woody biomass is equivalent to the carbon emissions from burning it. Thus, it is considered to be “closed loop” carbon.
Sounds like a good plan, right? Even the revered climate scientist James Hansen has endorsed the idea and warned us not to listen to knee-jerk Greens who seem to oppose anything that might diminish nature.
(1) Time matters (see figure below). The amount of carbon taken up to produce the woody biomass is equivalent to carbon emissions during burning. This is self-evident. But, the amount of wood used must not exceed the capacity of forests to regenerate and gain through photosynthesis an amount of carbon equivalent to that burned. To be truly carbon neutral, regeneration of forests must account for the biomass burned over time. Unfortunately, the amount of wood needed to fuel a power plant at an appropriate economy of scale can exceed the capacity of a region to regenerate from photosynthesis the biomass burned in a suitable timeframe.As shown in the graph below, the warming impact of emissions from woody biomass can be felt before this CO2 can be removed by regrowth. Yes, forests regrow, but it takes more than a decade for even fast-growing longleaf pine in the US Southeast to recapture the carbon emitted from their harvest and burning.
To understand this, imagine that we have decided to denude the Earth of trees, using wood rather than coal to produce electricity, and not replant the trees. Because burning wood releases more CO2 than coal to produce the same energy, the carbon emissions from these power plants would vastly increase the greenhouse gas burden of the atmosphere and accelerate the warming of our planet. Without the regrowth of these trees on a timescale that compensates for the rate of burning, we would rapidly make climate change much worse. Consider this: If emissions were sufficiently slow to allow for the regeneration of the burned coal and oil — say 65 million years or more — then fossil fuels would be carbon neutral. After all, coal and oil, like wood, are the products of photosynthesis.
The graph shows the release of CO2 from burning and the absorption of CO2 by photosynthesis for a given quantity of wood pellets. (Credit: Original model from the Natural Resources Defense Council; Image from Climate Central.)
(2) Additionality must always be included in the math. At times it seems that the jargon developed by the climate policy wonks is created to ensure confusion by the lay public. The term additionality applies to whether a project or activity creates “additional” emissions reductions that would not have occurred in the absence of the activity. To meet the requirement of additionality, project developers must be able to predict future emissions, and this has resulted in some spectacular mistakes in emissions accounting. Setting this conundrum aside, in the case of woody biomass one must deduct from the putative carbon savings of such closed-loop carbon the following fossil fuel emissions associated with a biomass power plant:
- Emissions from fossil fuels used in the transport of woody biomass to the plant
- Emissions from fossil fuels used in the harvest or collection of woody materials
- The embodied carbon emissions due to the construction of the plant — especially those associated with the fabrication of concrete
(3) Using waste wood seems to make more sense, but here again, the rate of regrowth matters and market forces can result in the cutting of living forests. The Gainesville Renewable Energy Center operates the woody biomass plant shown above, which claims to use (1) forestry residues and other products, (2) urban wood residue, (3) wood processing residue, and (4) other wood waste. Because these sources would otherwise decompose and become sources of greenhouse gas emissions, it seems reasonable to burn waste wood and derive energy from it. This idea seems terrific, but we must account for carbon loss and carbon gain over time. Obviously, decomposition is slower than combustion. If the waste wood is burned more quickly than new growth offsets the process after accounting for decay, then this fuel provides a limited improvement over burning trees.
Power plants have their greatest economic efficiency when they are large and serve many users. Thus, suppliers of waste wood will be tempted to maximize their profit margin through the convenience of using large volumes of harvested trees. It is no surprise that clearcutting of forests to feed biomass-fueled power plants is distressingly common, although I don’t know of evidence of this for the Gainesville plant. Certifying the sustainable source of fuel for biomass power plants requires rigorous regulation and oversight, including a quantitative accounting of the rates of regrowth, decomposition, and emissions.
Examples of the perverse outcomes of using woody biomass as a fuel are manifold. The use of woody biomass in Europe is supposedly regulated to be sustainable, but there is considerable evidence to the contrary. US forests are being cut to meet European demand. Nearly half of Europe’s renewable energy comes from wood, and in 2014, yearly wood pellet exports from the US to Europe had more than doubled in just a few years. The Europeans have institutionalized the practice of using woody biomass as a carbon-neutral fuel and the US Southeast has become by far the largest supplier. Negative impacts on biodiversity and forest health are driven by (1) conversion of forests to plantations, (2) intensification of harvesting, and (3) increased pressure on forests of high biodiversity value because saturated markets for pine pulpwood pushes the industry to harvest hardwoods. The Audubon Society notes the wholesale destruction of bird habitats in forests cleared to make wood pellets for Europe.
The Obama administration’s Clean Power Plan does not recognize woody biomass as a renewable energy source that states can use to meet mandated emissions restrictions. Based on the experience of Europe and the very real devastation caused by burning wood, this is wise policy. Congress, however, has not gotten the message. Our elected leaders lack the basic ecological literacy to question the claim that burning biomass is carbon neutral. This past summer, the two senators from Maine, Susan Collins, a Republican, and Angus King, an independent, introduced a bill in the Senate that would require the EPA not to count the carbon from woody biomass as a source of emissions. It is no accident that Collins and King represent a forested state in which the forest industries have progressively declined over the last few decades. Mill towns in Maine have gone from riches to rags. Using trees to make electricity could revive the economy of Maine, and be a boost to the economy of other heavily forested states. Presently, the proposed plan to force the EPA to allow woody biomass as part of the Clean Power Plan is faring very well in Congress, awaiting only reconciliation between versions passed by committees in the two houses before a final vote. Its enactment would spell disaster for our forests and the climate.
Meeting the goals of the Paris Agreement requires the development and global deployment of “negative emissions” technology to remove CO2 from the air. Included in this is a plan to create power plants capable of using biomass energy combined with carbon capture and sequestration (BECCS). Presently, only one such plant is operating at scale, but BECCS are a central feature of the Integrated Assessment Models (IAMs) used to inform policy makers. The emissions pledges of the participating states would allow the global average temperature to increase more than 3˚C above pre-industrial, while the goal of the IAMs is to keep warming below 2˚C, and an additional resolution was approved by the majority of states to target 1.5˚C. Using BECCS to achieve the necessary negative emissions would put vast areas of forest at risk. The promise embedded in the IAMs allows humanity to count on using negative emissions technology when it is more thoroughly developed and deployed while avoiding steep cuts in emissions now. There is an enormous risk (economists call this a moral hazard) that negative emissions technology will fail to deliver at such a large scale, and we will squander our window of opportunity to mitigate emissions in time to make a difference in global warming during this century.
The solution to our energy dilemma is increasingly apparent, and I can’t help but be astonished again how the politics and economics of the status quo continue to overwhelm the development of sound policy. The use of wind, water, and solar is the most promising pathway to worldwide fossil-free power generation by 2050. The works of Mark Jacobson at Stanford and the Rocky Mountain Institute show that such a strategy is a far less risky and a more direct means of climate mitigation than the BECCS or other technology-based means of achieving negative emissions. The issues of power intermittency and reliable baseload power have been largely solved through grid management and new storage technology. As I have argued in previous posts, careful management to maximize the biosphere’s capacity to take up CO2 through photosynthesis is the most reliable, direct, and cost-effective means of carbon capture and sequestration.
Unlike human mothers, Nature has no compassion for her slow-learning children. Physics is unaware of our jargon and models and has no need to negotiate with the authors of the IAMs. As seen in addiction, failure to fully accept reality can be fatal. I share with many scientists the certainty that we at the eleventh hour. We truly live in Decade Zero. Like the alcoholic who eagerly embraces recovery after having “a moment of clarity” about the reality of addiction, this is the time when we must make avoiding catastrophic climate change the organizing principle for civilization. There are extreme risks to allowing market forces and politics to constrain our solutions. The relatively weak emissions reductions promised by the participants in the Paris Agreement are much too little and too late. Even Obama has treated climate change as a seeming afterthought in his recent analysis of the world economic system. Global mobilization to address the climate crises is unavoidable. As individuals and constituents in the political process, I urge you to speak out and demand science-based solutions to salvage a livable planet for our kids and all future generations. Remaining silent at this point is more than irresponsible, it is ethically reprehensible to place this burden on our children.