The Department of Energy and Oak Ridge National Laboratory recently released an important update to their assessment on biomass availability. The “Billion Ton Update” catalogs the current and future availability of biomass to use for fuel or energy. The report is an impressive synthesis of data and models from across the agriculture and forestry sectors, and pulls together plausible estimates of the maximum sustainable scale of biomass harvest. These numbers help people understand how much biofuel and bioenergy could in principle be produced without causing environmental problems, and my colleagues have used some of the author’s earlier analysis as the basis for our own work.
However, like its predecessor, this report will likely be the source of some controversy. There is a lot to examine in a big report like this, and I expect to come back to some interesting details later, but the most basic thing people need to understand is what I would call the sunny side assumption.
Murphy’s famous law assumes that whatever can go wrong will. This report, on the other hand, puts aside all the things that could go wrong, and catalogs everything that could go right. This is life on the sunny side.
This is not to say the authors don’t know what can go wrong. They have worked hard to on their their models to ensure the biomass harvests they project avoid the dark and troubled side: excessive harvests that degrade soil productivity; unsustainable farm and forestry practices that pollute freshwater sources; conversion of natural ecosystems to monocultures that endanger wildlife habitat; new biomass uses that push existing industries off shore, indirectly expanding emissions through land use change. However, because the author’s have kept their focus squarely on the bright side, their report does not provide the risk assessment that is critical to understanding the possible negative impact of a large biomass-based energy sector. This is the darkness and strife that we also need to understand.
To make this bright side/dark side comparison more concrete, let’s look at an example: corn stover. Corn stover is the leaves and stalks that are left behind when corn is harvested. Since this stuff is already growing together with corn, cellulosic biofuel advocates, myself included, hope corn stover will be used to produce cellulosic biofuel without increasing the amount of land under cultivation, avoiding indirect land use emissions that have plagued crop based bofuels. The billion ton study suggests there is 85 million dry tons of stover that can be harvested in 2012 at a price of $60 a dry ton, or enough to produce 6.7 billion gallons of ethanol (using the yield of 79 gallons per dry ton from this 2011 NREL report). They forecast that by 2022 this number could grow to more than 120 million tons, enough to produce 9.5 billion gallons of ethanol, more than all the conventional ethanol produced in 2008 and more than half the Renewable Fuel Standard mandate for 2022 all without a single additional acre of crop-land. Sounds great, but what about the risks….
Corn stover left on the field after harvest provides important environmental functions, protecting the soil from erosion, returning nutrients to the soil and preserving soil carbon that ensures long term productivity. ORNL uses some models developed by the Natural Resource Conservation Service called Revised Universal Soil Loss Equation and the Wind Erosion Equation to calculate how much stover must be retained to avoid these pitfalls. There are two things that jump out at me when I look at their analysis. First, I was surprised to see sustainable removal rates higher than 60 or even 80 percent in much of the corn belt. I am more accustomed to hearing people talking about using 25-50 percent of the stover( see, for example, this article suggesting not more than 25 percent of stover should be removed or even this story POET posted recently). But perhaps the larger problem is that there is no guarantee the harvest restrictions ORNL used in their analysis will be followed in the real world. I am not a farmer, but what I read (here is a good place to start) says that changes in management practices will be required (for example reduced plowing, planting cover crops, using green manures and precise measurement of fertilizer requirements) to harvest a lot of corn stover without significant problems for both the farmer and those downstream. Experience with corn ethanol demonstrates that accelerated production will not necessarily be matched by accelerated adoption of conservation practices that mitigate increased stress on the environment. To stay on the sunny side we need to ensure that as biofuels expand the market for corn stover, conservation practices accelerate as well to mitigate potential problems associated with these more intense harvests.
Biofuels production from biomass will increases the demands we place on our agricultural and forestry system, so we will need to make changes to protect the health of our farms and forests. These changes are not the main subject of the Billion Ton report, but they can’t be neglected if we hope to realize the vision the billion ton report communicates without major environmental problems. Conservation practices can be supported with carrots or sticks, but we can’t afford to put blinders on just and hope that everything works out for the best.
What do you think would be the best way to get biofuels onto the sunny side of the street?
Photo: St. Chris