Around 1.1 million households in Germany use wood as their primary energy source. For fear of rising prices for gas and heating oil, many people have resorted to pellet heating or the wood chip variant, especially this year. Because heating with wood is not only considered to be comfortable, but also cheap, green and climate-neutral, because the carbon dioxide that is released into the atmosphere when it is burned is bound again by regrowing trees in sustainable forests.
Statements that Pierre Ibisch vehemently contradicts: Wood emits more CO2 than gas when it burns to generate the same amount of thermal energy, says the biologist from the Eberswalde University for Sustainable Development in ntv's "Climate Laboratory". Several German forests that were created specifically for the timber industry are already dying under stress and are being transformed from a carbon sink into a new source of CO2. Sustainability labels also mislead consumers when it comes to forests. Especially in North America, forest companies destroy healthy nature for the new German lifestyle trend. And in the end, supposedly clean fuels like wood also block the use of actually climate-neutral energy.
ntv.de: As a biologist, you are primarily concerned with the preservation of forests. Do you still enjoy sitting around the campfire?
Pierre Ibisch: We haven't managed to do that this year, but of course you can always use the fireplace in the garden.
But you also think that too much wood is burned in campfires, wood stoves and pellet heating systems in Germany?
In Germany, not necessarily the campfires are a problem, but the burning of wood on a large scale for energetic use. Especially on an industrial scale when it comes to power plants or private households.
But if people heat with wood, that's better than if they burn gas or even coal.
We have a big and well-known problem with climate change. Wood has a good image because it comes from the green forest and grows back when you take it. This is also theoretically correct, as when you cut down another tree, space becomes available in the forest for a new tree. It can grow and absorb CO2 again. This has worked in the past and hopefully will continue to work in the future, but we're not sure anymore. And if it works, then of course with a time delay. Now some say: "No, it happens at the same time! I take down one tree and the next one grows somewhere else! There is no delay!" That is not correct, regardless of whether we look at a single tree or the entire stock in Germany: the more wood we use, the more we reduce the biomass stock. It can grow back, but that takes time.
So trees that are felled or die should also be left in the forest?
Yes, because the carbon is bound in the biomass. When trees are alive or growing, photosynthesis occurs. It's a miraculous process: Trees absorb carbon dioxide from air and water and turn it into sugar, biomass, wood and so on. Oxygen is also produced as a waste product, which is great. But this process takes time. The more biomass we remove from this ecosystem, i.e. wood and thus carbon, the longer it takes for new carbon dioxide to be fixed. This is called "payback time" in wood burning science. A kind of carbon debt that you take on with the ecosystem. The ecosystem is kind enough to settle them, but it takes time.
How much exactly? We started the campfire: How many years will it take to pay our debt?
It depends on the quantity, the health and the age of the trees. If we cut down a tree that is 100 years old and 30 meters high, ideally it will take another 100 years until a similar tree is there. We're talking about decades. This is a problem because we are already reaching critical levels of carbon dioxide concentration in the atmosphere. We must prevent further emissions immediately. It doesn't matter whether they come from gas, coal or wood. That makes no difference in the atmosphere.
So we could heat with wood, but only when we have created a tolerable level of CO2 in the atmosphere?
Exactly. In the next 10, 20 or 30 years, ideally, we should freeze carbon emissions. In fact, we already know that this is no longer enough. The concentration is so high that rising temperatures set new processes in motion that release further reservoirs of carbon: methane in the soil because permafrost is thawing, forests suffer and may die, leading to further CO2 emissions. So it is not enough just to stabilize the CO2 concentration in the atmosphere. We need negative emissions. The question is how do you do that? Can the forest play a role if you let it continue to grow and fix more carbon? It's complicated, but we have to talk about it: What does the forest do for the climate if you don't use it?
The timber industry likes to see itself as a partial solution to the climate crisis. She says that wood is a wonderful raw material that we can use to replace others - for example in the construction industry. But you are of the opinion that the timber industry should first be stopped for 20 years?
Substitution and replacement is a critical issue. The idea is that if we burn wood instead of gas or coal, we gain because we leave non-renewable resources in the ground. But it is also true: CO2 goes straight into the atmosphere. This substitution can also have the opposite effect, namely when supposedly clean fuels such as wood prevent other emission-neutral energy sources such as heat pumps from being used. This technology has certainly been slowed down because other energy sources were cheaper.
Municipalities definitely present pellet power plants or wood chip thermal power plants as great achievements. Aren't they?
If we had built more solar systems, energy-saving passive houses or even active houses that produce more energy than they use, we wouldn't need this wood at all. Then we would be in a completely different position. The problem with burning wood instead of gas is that we are actually releasing more CO2 to produce the same amount of heat. This has to do with the fact that wood contains water. This water first has to evaporate and the wood has to be dried before it can produce the added value of heating energy.
On the other hand, what would the forest do if we didn't take the wood from it? The carbon is not only in the trees, but about half is in the soil. Even in old growth forests where the trees are no longer growing, carbon continues to be sequestered. For example through dead wood, which decomposes as a carbon compound and fills the soil with organic compounds. We stop this important process if we harvest a lot of wood. You have to calculate that.
Unlike the forest owners, the Ministry of the Environment does not consider wood to be a climate-neutral heating element. Because there the forest has already been planned for other emissions that also have to be offset.
If we are honest, the forest does not store CO2 to offset emissions from automobile traffic or other combustion. In fact, he's just trying to compensate for the historic loss of carbon from wood extraction. But of course, forests don't happily absorb more and more CO2 just because there is more and more in the air. Heat, drought and extreme weather can even cause problems for certain tree species. Then the opposite happens, the ecosystem turns from a carbon sink to a carbon source.
Areas like the Sauerland are strongly characterized by spruce monocultures, which were created to efficiently meet the demand for wood. These systems are very sensitive. When the spruces are pressured by heat, drought, or bark beetles, drop dead, or are swept away by storms and then harvested, that's a carbon issue. There is new data from an international consortium that shows: In North Rhine-Westphalia, the forests have turned from a sink to a source in the last 20 years, i.e. they emit more CO2 than they absorb.
Because the forests are dying?
Right. Then the whole calculation is in the bucket and also the story that the forest is the best climate protector. He's only that when he's healthy and growing. Due to warming, we are reaching critical limits in more and more regions of the world. Individual trees get problems or the whole ecosystem. We know cases where forests turn into steppes, bushes or semi-deserts. The longer we delay tackling the climate crisis, the more forests will be affected. On very hot and dry summer days, the air is basically hungry for water. This dries out the plant tissue and leaves. On such days you can actually measure how trees shrink because they lose water. However, they also do not grow without water and cannot fix any further carbon. And when the forest is not doing well, the ground warms up more. Then more carbon stocks are mobilized and released - a new source of greenhouse gases that is often overlooked and not yet properly measured.
The Association of Forest Owners says that much later firewood is produced anyway in the production of chipboard, paper or other wood products. Can't this waste be used in heating systems or power plants without hesitation?
The assumption is based on the fact that we take more or less large amounts of wood from the forest to build wood products. Ultimately, the question is: how much wood can be removed without weakening the forest? In Germany, some foresters are already talking about the fact that their forests have been severely felled. The microclimatic regulation is disturbed. It's very hot and dry. Trees that previously stood together, shaded each other and cooled through evaporation are now standing alone and dying from the heat.
So there is no point in buying a wooden table instead of a plastic one?
I do not want to speak out against the use of wood. We know forest companies that harvest wood and earn money with it. But especially in extreme years like the past, they take a very close look and consider: Can I fell this tree or should I leave it there because otherwise there would be a gap in the canopy that could cause problems for the remaining trees? You have to do this very carefully and can no longer rely on any income tables from the past. It's over. Accordingly, it should stand to reason that wood is more likely to be used for durable products such as cupboards and tables, which are passed on for 300 years. Instead, there was also this acceleration in the timber industry with more and more new trends and short-lived products. If the table ends up in the incinerator after 20 or 30 years, we haven't gained much.
The German Pellet Institute states that pellets in Germany come exclusively from sustainable forestry. No more wood is felled than grows back. If you heat like this, you still don't heat sustainably?
There are sustainability seals such as FSC and PEFC. They suggest that their wood comes from responsible management, but we in research cannot see how these seals are supposed to guarantee sustainable wood production. Much of what is implicitly promised is not even recorded. Many pellets also come from abroad, which has adjusted to the growing market in Germany and Europe. In North America, forestry companies have converted their semi-natural forests into "pellet plantations" for our sake. They are harvested by clear-cutting and brought to Europe by ship for a lot of money. Just so that we have supposedly climate-neutral fuel here.
Clara Pfeffer and Christian Herrmann spoke to Pierre Ibisch. The conversation has been shortened and smoothed for better understanding.
