Biomass Energy and Climate Change

The new administration in Washington is filled with climate change deniers.  They reject the consensus among scientists that human behaviors emitting greenhouse gases contribute significantly to climate change.  The reality — climate change is part of a larger problem better known as global change.  Over 9 billion humans, many living relatively sumptuous lifestyles like ours in the U.S., are changing how the planet functions.  Some geologists believe we have entered a new epoch, The Anthropocene (see my blog post, Open Season on Chickadees).

It is too important to our collective future to let the short-term vision of the anti-science administration in Washington reduce our commitment to getting climate change policy right.  I hope, before we cross a point of no return in global change, to see an administration and a Congress willing to address the problem seriously.

One important question in climate change policy is how to treat the use of wood and other biomass for the production of fuels.  This is obviously important to us in Maine because the state is so heavily forested and declining numbers of paper mills leave questions about how best to use our forest resources.  How should the emissions of carbon dioxide from burning wood to generate power be treated?  Is using wood different from using coal, oil, or natural gas when it comes to climate change?  A recent article in Science magazine reviews some of the controversies – “Is Wood a Green Source of Energy?”

There are two simple answers to this question.

No, burning wood is just like burning coal, oil, and natural gas.  One of the primary byproducts of burning any of these is carbon dioxide, the largest contributor to climate change.  In fact, burning wood produces more carbon dioxide per unit of power produced than burning any fossil fuels.  Or…

Yes, harvesting wood for energy production allows replanting and re-growing trees that remove carbon dioxide from the atmosphere, directly offsetting the emissions.  International climate change agreements to date have adopted this second approach, calling emissions from biomass “biogenic carbon” and treating them as carbon neutral sources of energy.  The article in Science prompts us to think about whether this is a good policy for the future once we have an administration not captured by energy industry special interests.

In the spirit of full disclosure, we heated our Maine home for nearly 25 years exclusively with wood burned in a wood stove, much of that wood harvested from our own wood lot.  That may be as close to carbon neutral energy as you can get.  But it is a far cry from the industrial production of electricity with wood pellets produced in Georgia and shipped to England discussed in the Science article.  Like the fallacy of counting corn ethanol use as a climate change mitigation strategy, I am convinced that wood as an energy source is far from carbon neutral.

When it comes to climate change policy we should treat biofuels the same way we treat coal, oil, and natural gas.  My preference is a carbon tax, taxing energy on the carbon emissions per unit of power delivered.  There are several reasons we should treat biofuels, whether they be wood pellets, ethanol, or biodiesel, in this manner.

First, even if the land where trees are harvested for fuel grows back into forests it is decades or even a century before the biomass has removed the carbon dioxide from the atmosphere emitted by the combustion.

Second, it is not just the carbon in the trees that matters, particularly in boreal forests like Maine.  Some of my best friends are soil scientists who remind me that in northern forests there may be as much carbon in the soils as there is in the biomass above ground.  Depending on how forests are harvested and otherwise managed, a little or a lot of this soil carbon can be released.  So it is not just the carbon emitted by the power plant when wood is burned that needs to be counted.  And if it is decades for carbon to return to biomass through tree growth, it is even longer for it to build back up in the soil — maybe never.

Third, it is not just the carbon released by the combustion of the wood and the respiration of soils that needs to be counted.  There are carbon emissions from fossil fuels used to harvest, transport, and process wood before it is burned.  All of these count for climate change as well, and that carbon is never to be replaced by tree re-growth.  The idea that it takes energy to produce fuels is why many scientists believe corn ethanol has a negative energy return on investment.  That is, it takes more energy to produce corn ethanol than is contained in the final product.

Finally, without getting too much into the technical weeds, biofuels in general and wood for power production in particular, have what Vaclav Smil calls a low power densityPower density may be the best single metric for comparing alternative energy resources.  It essentially measures how dense energy is in terms of space and time.  Powering modern industrial societies with wood creates a big footprint.

 Power Density — Source: Vaclav Smil

These four factors alone should make us wary of using wood for industrial energy production.  Of course, there are many other negative impacts from harvesting forests to burn wood to produce electricity.  There are potential landscape scale impacts on watershed function, biodiversity, outdoor recreation, and other biogeochemical cycles.

I am not arguing that we should never use plant products – trees, corn, sugar cane, or switchgrass – for producing energy.  All energy sources for modern society have adverse impacts of different sorts, including fossil fuels, biofuels, wind power, solar power, and nuclear power.  The best energy choice is always investing in efficiency, so-called negawatts.  Programs like Efficiency Maine should always be our first choice.  We can live high quality lives with less energy consumption.

When we do generate power, let’s not succumb to the mythology that biofuels have no climate impacts.  If and when we do address climate change seriously, biofuels should be treated honestly for what they are, a net contributor of greenhouse gases to the atmosphere.  They are not carbon neutral.

Mark W. Anderson

About Mark W. Anderson

I am proud to be a Mainer, born in Caribou and schooled at Brewer High School, Bowdoin College, and the University of Maine. I am grateful for a 35 year career at UMaine, the last decade in the School of Economics.