There is a growing enthusiasm for biomass, as pundits like Arne Jungjohann look at small towns in Europe that are able to get 100% of their energy by burning wood and other biomass. But when these cases are presented out of context, I’m afraid some may draw unwarrantedly optimistic conclusions.

Biomass power is not, in itself, a bad idea. It was a long time between the invention of fire and the use of anything but biomass to supplement muscle power for humans. Biomass has been part of the power mix for humans since well before our particular human species came into existence, and probably will to continue to be part of our power mix as long as our species exists. But it is also worth remembering that humans already make pretty extensive use of plant matter for food, fiber and power. A lot of that is grown or harvested in ways that are not sustainable in the long run.

Much of what we grow wastefully could be produced with care for long term limits; still it seems likely that the limits on what how much biomass we can turn to human use sustainably are somewhere between a bit less than we use now and a bit more. Since we are talking about European examples, let us look at United Nations report specifically on the limits of forestry in Europe, The European Forest Sector Outlook Study II(pdf).

The study looks at several possibilities. These include a reference case where biomass use increases about 35%, a biodiversity maximization scenario where biomass use increases about 19%, and a forestry carbon storage oriented policy where biomass use increases 55%. Given that Germany currently gets less than 7% of its energy from biomass, and Europe as a whole less, that does not make biomass any kind of magical solution to our energy problem.

If any of these numbers can truly be achieved sustainably, that is still far from worthless. They do suggest that the Germany in particular could get 10% or more of its energy sustainably from forestry. If true this adds a form of renewable energy usable for base, load following and peaking to the mix. The same would probably apply to the EU as a whole. Even if that is too optimistic, if the total sustainable percent is 7% or less, that still puts into the mix something that is renewable and still has flexibility equal to that from fossil fuel plants. It is simply important not to overestimate the sustainable potential of biomass.

Now it is important that this report also studies a fourth possibility, one aimed at maximizing wood and wood waste use for electricity. That scenario would almost triple current biomass consumption. But the policies that would achieve this include: importing plant matter from other nations, massive monocropping (though still preserving protecting areas), a massive increased use of fertilizers, pesticides and irrigation in forestry, harvesting trees young. This would result in a major loss of biodiversity, less soil carbon, less carbon in living trees, and in essence turn many forests into tree plantations. Although the report evaluation of the results seem to indicate little increased vulnerability to fire or pests, I find it difficult to see how less biodiversity in tree populations, poorer soil and younger trees could fail to increase both vulnerabilities.

Here is the bottom line. There are many forms of renewable energy we can use. But if we want to save our civilization without waiting for magic breakthroughs most of our future energy will have to come from four sources: efficiency, conservation, solar power and wind power. Many other sources will play important roles. But these other sources will be supplements. In the absence of unanticipated breakthroughs, efficiency, conservation, solar power and wind power will constitute the vast majority of our future energy mix if we wish to survive.