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Thursday, April 19, 2012

Forest Bioenergy Sustainability...What is the right level?

This was the title of the article that came across the news wire today:
"Analysis raises atmospheric, ecologic and economic doubts about forest bioenergy"
That sounds pretty dire, and I'm sure will be used by anti-wooders to their advantage. The article, as is usually the case, was too brief to understand precisely, so I clicked over and read the full paper, published in the journal Global Change Biology: Bioenergy. The paper as published was an invited editorial entitled "Large-scale bioenergy from additional harvest of forest biomass is neither sustainable nor greenhouse gas neutral". 
"Owing to the peculiarities of forest net primary production humans would appropriate ca. 60% of the global increment of woody biomass if forest biomass were to produce 20% of current global primary energy supply. We argue that such an increase in biomass harvest would result in younger forests, lower biomass pools, depleted soil nutrient stocks and a loss of other ecosystem functions. The proposed strategy is likely to miss its main objective, i.e. to reduce greenhouse gas (GHG) emissions, because it would result in a reduction of biomass pools that may take decades to centuries to be paid back by fossil fuel substitution, if paid back at all. Eventually, depleted soil fertility will make the production unsustainable and require fertilization, which in turn increases GHG emissions due to N2O emissions. Hence, large-scale production of bioenergy from forest biomass is neither sustainable nor GHG neutral."

Now, you might think that a proponent of biomass energy, such as I, would go to great pains to dissect and challenge this article. Not so. In fact, I believe the authors of the paper are contributing a valid issue to the bioenergy discussion, simply from the specific use of the qualifier "Large-scale bioenergy" in their title. You see, the gist of their article is, that large-scale biomass energy doesn't make sense, which is precisely what I proposed in past posts like Size Matters. The difference in their point is that they believe large-scale is not globally sustainable from an ecological standpoint, and I believe that it is not locally sustainable from an economic standpoint. So, for different reasons, we agree that size matters.

The debatable point is what "large-scale" means. The authors of this paper, I believe, are basing their definition of large-scale on the proposed production level of bioenergy targeted by many governments, including the United States. They point out that many European countries have targets of 20% of primary energy production to come from bioenergy. Further, the recent update to the USDA's Billion-Ton Supply study essentially lays out a road map by which our primary energy production from biomass could more than double by the year 2030. 
This graph from the Billion-Ton Supply paper illustrates part of the equation. In it, we see that currently, about 4% of our primary energy supply comes from biomass feedstock. Of this 4%, less than half comes from forest biomass; the total includes a current consumption of about 200 million tons of forest biomass out of a total of about 450-500 million tons of total biomass. The study examines the resource economics behind possible scenarios that increase that total biomass consumption for energy to about 1 billion tons by 2030, or more than twice the current biomass usage.
But a significant portion of that projection comes from ethanol and other energy products from agricultural energy crops, which have different sustainability issues than forest biomass. In the above figure from the Billion-Ton update, we see that the forest component (blue and red components of the bars) of the projected supply only increases from the current 200 million-ton level to about 350 million tons.  Additional wood biomass is included in the green "energy crop" component of the bars, and these energy crops include short rotation poplar, willow, eucalyptus, and southern pine in dedicated energy plantations. You can see that this component of the potential supply is practically non-existent now, but would need to grow to roughly the size of the forest biomass component for the total to reach one billion tons.

So, let us clarify that the USDA Billion-Ton Study is not suggesting that we could or should produce 20% of our primary energy from natural forests, or even natural forests plus short-rotation woody crops. The 2030 projection would increase our forest energy production from about 2%, currently, to about 3.5% of our primary energy production, far short of the 20% argued against by the authors of the paper cited at the top of the post. When woody energy crop production is included (let's assume half of the green component above, the other half going to agricultural crops), that means in essence that the USDA report is suggesting in reality that about 5% of our primary energy production could be sustainably produced from forest production and short-rotation woody crops combined.

So, the recent paper argues a straw man position that I think most natural resource scientists would agree with...that our forest resources are not capable of sustainably producing 20% of the world's primary energy supply. They are correct in suggesting that attempts by governments to impose a 20% target of this nature, and to therefore encourage "large-scale" wood energy projects, especially large-scale power, are misguided and will not achieve the ecological impacts they are hoping for.

But I think we have ample room under the "biomass cap" to work with at this point. Once we get closer to 5%, which seems to be, with our best projections (for the United States, at least) a sweet spot on woody biomass energy production, we will be pushing the limits of our biomass energy capabilities, and the energy markets will certainly be pushing back, due to the increasing price of biomass at that level.

Helpfully, the discussion started by these scientists sets an outer limit for our discussion. We know 20% woody biomass energy is too "large-scale" from a ecological standpoint; we know that here in the U.S., 2% is what we currently do; and we know that 5% is "doable", at least from the production standpoint. Would the authors argue that 5% is as ecologically unsustainable as 20%?

Probably not. But their points set some nice boundaries for future research. What is the right level? Only our future scientists and wood producers will be able to answer that with a reasonable level of certainty. Until then, let's not push the biomass bandwagon too hard... we might hit a wall where none was expected. But let's not unnecessarily constrain it, either. Let's just keep moving it down the road at the rate that the energy markets will comfortably allow.


Marc McDill said...

Good post, Chuck.
~Marc McDill

John Karakash said...

I appreciate your pointing to scale as a critical factor. It's hard to understand what are people thinking? The economics don't work for big projects given the cost of freight and low price for contract electricity or liquid fuels. Keep it up Chuck.

Li said...

This article is similar to Manomet study at some point, the presumption is that when a plot of forest is selected and then every single tree is harvested from it, carbon sequestered in the exact same plot can counted as pay off carbon debt. In actual forest systems, assuming sustainable forestry practices, the carbon released by combustion is sequestered by carbon accumulation from the rest of the continuous forest growth. The article is using “debt-then-dividend” model, why we couldn't use "dividend-then-debt" model? It is like if you only use credit card, you are always in debt; but if you only use debit card, you never have debt.

Jeff Wartluft said...

And then there is energy demand which was not mentioned. And changes therein would (will) change everything. We are all a part of the demand. And the demand seems unreasonable - most of us want big homes, airconditioned and heated and lighted to perfection, along with our multiple vehicles and play toys. Where does it all end? Birth rates and lust for energy play havoc with forcasts. The human factor is always the toughest to deal with. A few years ago the population was expected to grow by 25% by the year 2020. But the energy demand was expected to grow by 40% in the same period of time.

Anonymous said...

Thanks for taking such a reasonable approach to this issue, and acknowledging that some assumptions about the role of forest-sourced biomass go a bit overboard. Given reasonable supply expectations, we can prioritize the uses that get the most energy bang for the limited wood buck. In colder climes, small-scale heating uses seem to fit the bill, and we may want to think twice about subsidizing large wood-fired electricity or biofuels plants or committing to long-term export contracts with European coal plants. Once we get the policies balanced among energy sectors, the subsidies that allow those uses to pencil out financially could well disappear.