The fundamental idea behind bioenergy is that it’s carbon-neutral because it releases the carbon that plants absorb when they grow, and thus does not add carbon to the air. Why is this wrong?
It’s a common misunderstanding. Burning biomass of course emits carbon, just like burning fossil fuels. The assumption is that the plant growth to produce that biomass offsets the emissions. But the first requirement for a valid offset, whether for carbon or anything else, is that it is additional. If your employer wants to offset your overtime with vacation, they have to give you additional vacation, not just count the vacation you’ve already earned. Similarly, you can’t count plant growth as an offset if it was occurring anyway. Plant growth can only offset energy emissions if it is additional. Counting plants that would grow anyway is a form of double-counting.
Can you explain more what you mean by double-counting? Plants regrow, so why doesn’t that make them carbon-neutral?
Your paycheck provides a good analogy. Say you get paid every two weeks. You spend your paycheck, and the good news is you’ll get your next paycheck in another two weeks. Ok, so what if I say, “Give me your paycheck. It’s not going to cost you anything because you’ll get another paycheck in two weeks.” Of course, unless you are pretty foolish, you are not going to give me your paycheck because you’re using your paycheck to pay rent, buy food, and perhaps store some money in the bank. Giving me your check therefore comes at a high cost. It’s the same with plant growth and the carbon it absorbs. We use these plants and their carbon for food, housing, or as forests, which are like a carbon bank. The only way for you to get richer in money is to get a bigger paycheck, and the only way to get richer in carbon is to produce more plant growth. Just using plants differently (as in the case of bioenergy) sacrifices using them for another purpose. That’s the fundamental intuitive error people make when it comes to bioenergy.
When did using wood in power plants become a major part of the global energy conversation?
It wasn’t until pretty recently that anyone thought it was a good idea to burn anything other than just waste wood material for electricity. It almost started by accident: what happened was Europe adopted rules that treated any biomass as automatically carbon-free regardless of where it came from. Power plants started buying wood pellets made from whole trees or portions of trees. Forest owners then realized they could make a lot of money and started backing the idea, too. But none of the environmental assessments said it would be good to chop down trees - they were all based on the assumption that the industry would use forest waste.
This is a case where an accounting error gave rise to an industry, which then sought to justify itself. If you talk to the industry today they claim they’re using waste materials, even though it’s not true, it’s just a semantic distinction.
So the biomass industry isn’t actually using waste materials? What are they using?
For something to be a residue, it has to be something that would otherwise be left in the forest and not used for another purpose. That’s a very, very small amount of wood; it’s basically just the tops of branches that are too small and leafy to provide decent wood pulp. Unfortunately, when the industry talks about residues, it’s primarily talking about pulp-quality wood. But if you divert pulpwood to bioenergy, that means you’re going to have to cut down trees for pulp elsewhere.
But what if you grow biomass on marginal lands, where it wouldn’t be displacing primary forest or good agricultural land?
First of all, these so-called “marginal lands” don’t actually exist. The studies claiming that there are large areas of marginal land are doing a related form of double-counting. Many such claims start with an estimate of potential cropland in the world, subtract the amount being used, and call the rest “marginal.” But that includes much of the world’s forest! Other estimates subtract the area of dense forest, but what remains as “marginal” lands are actually wetter grazing lands that are already being used to raise animals for food production, or woodland savannas that are home to enormous biodiversity and large volumes of carbon. That is, in one form or another, they are already providing benefits. If you convert woody savannas to bioenergy you lose a huge amount of carbon. My colleagues and I did a study that found if the wet savannas of Africa were converted even to cellulosic bioenergy, there would be major greenhouse gas consequences for decades on nearly all the land.
Ok, so the problem with bioenergy is that it requires large land areas. What if we just do a small amount of biomass?
Two problems. First, there is always an opportunity cost, since that land could be used instead for food production or storing carbon. Given that we are likely going to have to increase food production by 70% or more, productive land is extremely valuable. Using a small amount of that productive land will only get you a small amount of bioenergy, and you lose something worth more in the bargain.
The second problem is that even a small amount of bioenergy requires a huge amount of biomass, and therefore land. For example, if you took all commercial tree harvests in the world today and diverted them for bioenergy, it would only provide about three percent of global energy. That is, to produce just three percent more of the world’s energy, think of all the effects of forestry on the world’s forests, and then double those impacts.
Why do so many studies show a huge potential for bioenergy growth?
The first way is by double-counting land that is already being used either for food, timber, or storing carbon. The marginal land examples are one way in which that double-counting happens. Beyond that, large bioenergy estimates are based on a theoretical technical potential, which in reality shouldn’t mean very much. There are very few problems in the world that we couldn’t solve if all we cared about was technical potential. I mean, we have the technical potential to educate every person in the world, or to fed everyone nothing but steak three meals a day, or to produce many times our energy demand from wind and solar. But that’s not the issue - what is the realistic potential, facing economic and practical constraints? The truth is the potential for bioenergy is very limited.
How does bioenergy compare to other renewable energy sources?
Biomass produces energy via photosynthesis, which is ultimately a way of converting solar radiation into usable energy. However, photosynthesis is remarkably inefficient and requires land, plenty of rain, and warm temperatures. The good news is that photovoltaics are a dramatically more efficient way of making energy from solar radiation, and they are becoming more efficient and cheaper all the time. We did a calculation that showed that even if you’re foolish enough to use the world’s most productive agricultural land in Brazil for solar PV, you’d still produce on the order of thirty times as much energy as you would get from sugarcane for biofuel. The lesson is, if you want to produce energy from solar radiation, cut out the middleman – a very bad middleman. Photosynthesis is the only way to make energy to feed ourselves, and the only way we can produce trees, but it’s a really lousy way to produce energy.
Is bioenergy a more appealing option in developing countries?
In many parts of the world, poor people use bioenergy (i.e. wood or dung) because they have no other energy options. If all modern bioenergy did was replace this traditional bioenergy with more efficient bioenergy, that would be good. But that’s not what’s happening. Indonesia, for example, wants to expand its use of biodiesel from palm oil, which is a major crop there. From a carbon perspective, though, biofuels are worse than using fossil fuels. Indonesia is the most obvious example, because much of the palm oil is grown on carbon-rich peat forest. While it’s true that Indonesia has some already cut-over forest that could be used to grow palm oil, that oil should go to meet rapidly growing food demand, not biofuel.
What does the IPCC say about the role of bioenergy in climate mitigation?
In the last IPCC report there was a bioenergy group that was asked to contribute to the mitigation section. It included people who are both critical and supportive of bioenergy, and the two groups basically fought themselves to a draw. That compromise, however, still leaves the impression that you can have a lot of bioenergy. For example, if the advocates are claiming you can have 500 exajoules (EJ) of bioenergy per year and the critics are says you should have zero, then the middle number they land on is 250 EJ. That is hardly a middle number. It is roughly equal to 100% of all the energy in all the crops the world harvests each year, as well as all the timber, all the crop residues, and all the grass eaten by livestock.
Has the IPCC’s stance on bioenergy changed over time?
The IPCC report back in 2001 had an estimate that we could produce all human energy from bioenergy, which was based on the error I mentioned earlier about how “potential cropland” is defined. The area they assumed would literally include the entire Amazon and the Congo basin - it’s essentially all of the world’s good land that isn’t already crops. If you make an assumption that land is automatically free, then you end up with bad conclusions.
What about “third-generation” biofuels made from algae? Could they solve the land problem?
It would be great if the world could produce algae efficiently, but it is not going to be a significant source of energy. When you actually look at the amount of water, nitrogen, and even land that algae will require, even with optimistic estimates, it is still a lot. Even supposing we can produce algae cheaply enough, we wouldn’t want to burn it. Algae produce a high protein feed that could be used as an animal feed or as oils for aquaculture feeds. Using algae for biofuel would be like burning meat!
Why do you think some scientists still advocate for bioenergy?
One reason is that it would be much easier to solve climate change if there were very large quantities of free land or carbon-free biomass sitting around just waiting to be used. Another is that science got caught in this double-counting error, and it takes a while to get rid of it. Even though nobody denies the double-counting problem anymore, new arguments have arisen. For example, some scientific biofuel enthusiasts claim that we can produce vastly more food on vastly less land, and should then use the remainder for bioenergy. Unfortunately, that’s very unlikely to happen, but even if it were, we should wait to see this free land before dedicating it to bioenergy. And even in that case, we would still be much better off allowing that land to reforest and using solar energy on dry land to produce our energy.
Tim Searchinger is a Research Scholar at the Woodrow Wilson School of Princeton University. He is also a Senior Fellow at the World Resources Institute. You can read more about his work and view his publications here.