The Economy, Land & Climate Podcast

Why bioenergy increases CO2 emissions even more than burning coal - with MIT's John Sterman

February 11, 2022 Economy Land & Climate Insight Team
The Economy, Land & Climate Podcast
Why bioenergy increases CO2 emissions even more than burning coal - with MIT's John Sterman
Show Notes Transcript

Alasdair talks to John Sterman about his groundbreaking research that proved burning wood for energy will "increase atmospheric CO2 for at least a century".

John Sterman is the Jay W. Forrester Professor of Management at the MIT Sloan School of Management, the Director of the MIT System Dynamics Group and the Director of the MIT Sloan Sustainability Initiative. His team developed a model for dynamic bioenergy lifecycle analysis, which he hoped would prove burning "wood was part of the solution" for the climate. Instead, "it came out the other way".

Further reading:

·         Professor Sterman’s paper about the outcomes from his bioenergy modelling
·         More details on the study, in reply to a comment on the paper
·         En-Roads, MIT Sustainability Initiative’s interactive climate simulator that allows users to explore the impacts of different climate policies
·       Read more about bioenergy and BECCS, and listen to more podcasts on the topic, in ELCI's bioenergy hub






Alasdair:

Hello, and welcome to the Economy, Land and Climate podcast. My name is Alasdair MacEwen, and in this episode we decided to explore the issues raised in previous podcasts on the use of bioenergy, and to delve further into the scientific evidence about its impact on our climate. I met with Professor John Sterman from the MIT Sloan School of Management in the US to ask him about his groundbreaking research on wood burning.

John:

When you harvest and burn trees to make power, you're putting carbon in the air right now today, more than fossil fuels. And regrowth takes a very long time. And it's not certain. It's really just that simple.

Alasdair:

I started by asking Professor Sterman about his current work, and how he got into researching bioenergy.

John:

I'm faculty at the MIT Sloan School of Management. But my field is dynamic systems, and computer simulations. So what we do - our field is called system dynamics - and what we do is we develop simulation models of any kind of dynamical system. Here being at the Sloan School, the Management School, we tend to focus on important human systems and human systems as they interact with the natural world. I am codirector of our MIT Sloan Sustainability Initiative. So we're looking at climate change. We're looking at wood bioenergy that we're going to talk about today. We look at all kinds of issues where there's important interactions between people; people in organisations, companies, markets, supply chains, for example, and the natural world that is supplying all the inputs that they need in order to run their business, their industry and the economy, and the wastes and outputs, the fate of them across the entire lifecycle.

Alasdair:

How did you get into working in that area?

John:

So I actually started when I was in high school, but really took off when I was an undergraduate. And I was very interested in what we today call sustainability, but we didn't have that word back in the 1970s. So it's been a passion of mine for my whole career.

Alasdair:

You published what is arguably seen as a very significant piece of work around the burning of wood for power. I'll maybe let you just go into the detail around it. If you could just tell us a little bit about your research into bioenergy, that'd be great.

John:

Sure. So first of all, this is work that I've done with colleagues; Professor Juliet Rooney-Varga at the University of Massachusetts in Lowell, and Dr. Lori Siegel, who is the Chief Modeler for Climate Interactive, which is a nonprofit think tank we partner with. And what we did is we built an interactive simulation model, the wood bioenergy supply chain combustion, and compared that against the supply chain for fossil fuels, including coal. And when we started out, I sincerely hoped that wood as a renewable source of energy, potentially renewable, would prove to be an important contributor to addressing the climate challenge. The climate crisis is so dire, and we've waited so long to do anything meaningful to cut our greenhouse gas emissions that I really hoped that it would turn out that wood was part of the solution. Unfortunately, it came out the other way. And we can talk about why that is. This was disappointing, but it is what it is. And we had to publish the results that the science indicated. I'll also say that we are one of many research groups and scientists around the world who have been looking at this issue and the overwhelming consensus is similar to ours, that burning trees to generate power, electricity and heat actually makes climate change worse for at least many decades, and possibly, for a much longer time after the end of the century.

Alasdair:

And can you go into a little bit about the the comparisons that you made with coal?

John:

To answer the question of whether wood as a source of electricity or heat is better or worse than any other fuel, including coal, you have to answer a couple of questions. First, you need to know what the lifecycle emissions are. When you mine coal, process it, ship it to a power plant and then burn it, what are the greenhouse gas emissions associated with each step of that process? And you need to do the same analysis for harvesting wood from forests, processing it, shipping it, burning it. That's the domain of traditional lifecycle analysis. But the second thing you have to do is you have to analyse the dynamics of potential forest regrowth. The coal has been sequestered underground for millions of years. When you burn it, that CO2 goes into the active carbon cycle immediately on combustion. So does the CO2 from the wood, but the forests might regrow. And you need to know well, how long does that take? How much carbon is removed from the atmosphere by the potential regrowth of the forests that you're harvesting to supply that wood? So when you combine those two kinds of analysis, what you've got is what we call dynamic lifecycle analysis. And so we developed a simulation model that does that. The scenarios you can test, and the model is publicly available with the underlying papers, it's been replicated by other folks, you can get the model and run your own experiments. But the basic scenario we looked at is, what if you were to displace the combustion of coal to generate electricity with an amount of wood that would generate the same amount of electricity? And then what we're able to do is see what happens to total greenhouse gas emissions, carbon dioxide emissions in particular. And here's where the two kinds of analysis come together. So the first thing is, the amount of carbon dioxide released per kilowatt hour of electric power from wood is larger than from coal. So to produce one kilowatt hour from coal, you generate less CO2, than if you produce a kilowatt hour from burning wood. Now, the coal is producing a lot of CO2, let's be clear, and we have to phase out not just phase down - as Glasgow indicated - coal as fast as possible. It is the most carbon intensive fossil fuel. But burning wood actually puts more CO2 into the air per kilowatt hour than burning that coal. The reasons for that are, first of all, there's a great deal of water in the wood, and it takes energy to boil off that water, and that reduces the efficiency of combustion. And it takes more energy to break the chemical bonds in the wood than to break the carbon carbon bonds in the coal. So when you burn that wood, you're actually producing more carbon dioxide immediately than burning even coal. And if you're displacing fuel oil, or propane, or natural gas, then there's an incredible increase in the emissions from the wood. Just to give you an

example:

25% more carbon dioxide per BTU or joule from wood than for fuel oil. And that's just for the energy content that's not counting the efficiency losses in generating electricity, which makes it even worse. 50% more carbon dioxide per BUT or joule than burning propane and 75% more than burning natural gas. In some parts of the world, wood is being used to offset coal. Even there, you're generating more carbon dioxide per kilowatt hour than if you continue to burn the coal. But in many places, for example, where I live here in New England, natural gas is the marginal source of electrical generation or it's renewables. And so if a biomass plant is built here, and people have tried to do that lately, you will be spewing a huge amount more carbon dioxide into the atmosphere immediately, compared to burning that natural gas. Now the question is what happens with regrowth? You harvest trees, you process them into chips or pellets, you ship them to a power plant, you burn them instead of coal, say, and the amount of carbon dioxide in the atmosphere immediately goes up by more. And that creates what's called a carbon debt. Now the forest might regrow. But the key thing here is regrowth takes many decades, and regrowth is not certain. And in the meantime, even if regrowth occurs, the amount of carbon dioxide in the atmosphere is higher than it would have been without the wood. And so climate change is accelerated. It's made worse. Now, if the forests regrow, you get to a point eventually where the extra carbon that was injected by burning the wood has now been removed as the forest grew back. How long that takes is called the carbon debt repayment time. It varies with the species and it varies with the climate zone you're in. But our analysis looking at a wide range of forests in the United States, forests that are today being used to supply pellets to bioenergy plants in the UK, and in Europe and other places, we found that the carbon dead payback time was between 40 and more than 100 years. And we just don't have that kind of time. What we know from the IPCC and other scientific analyses is that in order to get on a pathway that will limit the amount of warming to no more than two degrees C, and striving for 1.5, the targets that essentially every nation in the world has agreed to - total global greenhouse emissions need to fall by close to half by 2030, and reach approximately net zero by mid century. Well, that's just a couple decades away, it's a lot faster than the carbon dead payback times from burning wood. So what that means is, although it seems obvious to everybody that it's got to be better to burn trees than coal, because the trees are a renewable resource, they can grow back, it turns out over the timeframe we've got that doing that will make climate change worse.

Alasdair:

Okay, that that's very interesting. The implications of that are startling. What has the reaction of the biomass industry been to your research?

John:

Well, obviously, I can't speak exactly to what their view is, you should ask them. But generally speaking, they have not welcomed the research that we and many others have done showing that you actually make things worse for many, many, many decades, or even to the end of the century and beyond. They have a vested interest, of course, in promoting wood as a power source, because they're profiting from this both because they are able to sell that power, but also because they're heavily subsidised. This is a consequence in the European Union and in the UK, of the EU's declaration that all biofuels are to be considered carbon neutral. That's just not true. Especially for wood. Things that grow back faster; this problem of the carbon debt payback time being very long is much less severe. There are still issues. If you're burning straw, say, or growing switchgrass or some other sugarcane bagasse, these bio feedstocks that can grow back on an annual basis or much, much faster than trees can grow. There are still issues around that - they take up land that might be needed for crops or pasture, they may need to be fertilised or have pesticides and herbicides applied and that creates other environmental problems. And there are many scientists who look at these issues, Tim Searchinger at Princeton, John DeCicco at Michigan, they are experts in these areas. And they have also found that certain kinds of fast growing biofuel, feedstocks actually makes climate change worse, unless people go hungry. Because you need a lot more land to produce those fast growing biofeedstocks. And you run the risk of then compromising the land and and the crops that are available for food. But with wood, it's much much simpler. When you harvest and burn trees to make power. You're putting carbon in the air right now today, more than fossil fuels. And regrowth takes a very long time. And it's not certain. It's really just that simple.

Alasdair:

So are you surprised that global bioenergy use appears to be growing? Nevertheless, you know, despite your research?

John:

Well, I'm both not terribly surprised, and I'm disappointed. The regulation that the EU has; what it does is it allows a power plant that's burning wood to ignore completely the CO2 resulting from burning those trees on the assumption that because it's renewable, it's offset somewhere else in the forests that are harvested to supply that wood. The problem is, that's just not true, because of the timing issues that we just talked about. So there's a major loophole. So for example, when power plants in the UK have switched from coal to wood, under the rules that they operate under - so this is all legal - they get subsidised to do that, to switch to wood. And the carbon accounting doesn't count the emissions from burning that wood and so it appears that emissions of carbon dioxide in the UK have fallen, even though the emissions from burning those pellets have increased above what they were before. This is a loophole and it needs to be closed. But so far the EU and the UK have not been willing to do that.

Alasdair:

And I realise that you're not a policymaker, but I suppose this is what you're pointing to. The possible policy solutions around biomass, I mean, it would be closing those loopholes. Is that fair?

John:

Sure. Absolutely. Accounting rules are inconsistent with the biogeochemical realities. And they don't account for the long time delays and regrowth and they also don't account for the uncertainty. So regrowth takes a long time. But it's also not certain. You could be a conscientious landowner and harvest some wood for bioenergy, and then allow your land to grow back as a forest. But there's no guarantee that that will happen. First of all, you could cut down those trees much earlier, before the carbon debt is paid back. And then whatever carbon in that wood there is goes back into the atmosphere. Or, more importantly, you face the risk of wildfire, pests, disease, extreme weather, that can kill those trees, knock them down, prevent their regrowth and all of those risks are increasing with climate change. So we actually see this - the data are clear the risks of all these hazards to regrow the forests have increased over the past few decades, and they're only going to get worse as global warming and climate change continue. And so accounting needs to recognise these two basic facts. Regrowth takes a long time if it happens at all, and it's not certain.

Alasdair:

My thanks to Professor John Sterman for his time. We've published along with this podcast some further reading around his research, as well as Professor Sterman's most recent work on his accessible climate change policy simulator, which you can try through the provided web link. Do visit our website for other climate policy related reading. Thanks for listening!