At first glance, there are good reasons for heating with wood. It is considered cosy, cheaper than gas and sustainable. In Germany, wood is treated as a climate-friendly fuel and renewable energy. The reason: The carbon dioxide (CO₂) that is released into the atmosphere when wood is burned is bound again by regrowing trees in sustainable forest management.
Increased demand for wood as fuel
According to the Federal Ministry of Food and Agriculture (BMEL), more than a million households in Germany use firewood, wood pellets – i.e. pressed wood in a cylinder shape – or woodchips as the primary energy source for heating the entire living space. In addition, there are over eleven million so-called single-room fireplaces such as stoves (as of March 2022).
So far, wood has played a rather subordinate role: According to the Federal Statistical Office, in 2021 only 3.6 percent of new buildings used wood as the primary heating energy source. The effects of the Ukraine war on gas prices could change that. That sounds good at first, like a win-win-win situation for people, industry and nature. However, many experts see things differently.
Greater release of pollutants
Some scientists consider burning wood a hazard to human health. So does Achim Dittler from the Institute for Mechanical Process Engineering and Mechanics at the Karlsruhe Institute of Technology (KIT). “Nothing burns dirtier and more harmful to the climate than wood,” says the researcher. Burning wood would release many more pollutants than burning oil or gas, including carbon monoxide, nitrogen oxides and methane. And the highly concentrated gases and harmful solid emissions such as soot would have devastating consequences for air quality.
Among other things, Dittler was involved in drafting the Leopoldina’s “Clean Air” statement from 2019.
According to the aerosol expert, it is most problematic when the smoke flows directly to neighboring houses and gets inside via technical ventilation systems even with the windows closed. “Then you will experience that your own living space can become a dangerous smoke trap due to wood stove smoke.”
From his point of view, pellets have at least one advantage over split logs: due to the uniform size and the manufacturing process, the fuel quality is more uniform, and they also burn in a controlled manner in the stove. As a result, the smoke development is more controllable than with split logs. Although the pollutant concentrations are lower than with a log stove, they are still significantly higher than with gas heating.
Dittler calls it a “cardinal error” that, despite all the facts, wood energy in Germany is described as climate-neutral, sustainable energy. The Federal Ministry of Economics and Climate Protection also reports on request that the emission of air pollutants from wood firing is a problem. For this reason, the rules for keeping the air clean when installing and operating wood heating systems have been tightened again this year.
“Calculated, more people will get sick”
Wolfgang Straff, Head of the Department of Environmental Medicine and Health Assessment at the Federal Environment Agency, specifically warns of the health hazards caused by particulate matter. “In general and regardless of the source, the inhalation of fine dust leads to a relatively high burden of disease in the population.” For example, cases of lung cancer and other diseases such as cardiovascular diseases and diabetes can be attributed to particulate matter. According to the doctor, between 2010 and 2018, an average of around 17,500 deaths per year were caused by particulate matter in Germany.
The emissions from wood-burning stoves are no small matter, as the Federal Environment Agency calculates: “Example of fine dust: A new wood-burning stove of normal size, when operated at full load, emits around 500 mg of dust in one hour. That corresponds to approx. 100 km of driving in a passenger car Emissions standard Euro 6.”
The burning of wood is already responsible for around 20 percent of German particulate matter emissions. What will happen if more people heat with wood this winter? “All in all, many people will breathe in even more fine dust than in recent years, and this means that more people will get sick.” Nevertheless, the doctor understands that many people have money worries and therefore switch to the supposedly cheaper wood. “It’s a dilemma. We humans feel the cold immediately, while we can’t perceive the other health risks.”
Devastating effects on forests
So should heating with wood be banned in the future, as some experts are demanding? After all, burning wood is not only risky for human health – environmentalists warn of the devastating effects on forests. If Pierre Ibisch from the Eberswalde University for Sustainable Development had his way, the promotion of wood burning should be stopped immediately. Because burning trees is only climate-neutral under certain circumstances.
On the one hand, if no greenhouse gases streamed out of the forest floor when they were removed. “Approximately half of the carbon in forest ecosystems is in the soil,” explains the ecologist. Drying out and warming favored the unwanted breakdown of the carbon, which was then released as CO₂. Secondly, the claimed climate neutrality applies at best over longer periods of time and under the condition that harvested trees really grow back. Even then, plantations with newly planted trees would only become effective carbon sinks with a time lag.
Forests are additionally weakened in the climate crisis
Compensating for the “carbon debt” that has arisen will take at least decades. “But we need the immediate avoidance of additional greenhouse gases.” Ibisch, who has been researching the consequences of climate change for ecosystems for 20 years, sees wood burning as a major threat to the future of forests, which are in a poor state anyway.
As a result of the consequences of the climate crisis and forest use, the productivity of the trees is falling. “So while the trees grow worse, we want to use more wood. A fatal combination,” warns the forest expert. “Heating with wood means: Biodiversity, soil and microclimate are deteriorating – and of all things in the climate crisis.”
According to the Federal Environment Agency (UBA), almost half of the wood currently used in Germany is used to generate energy. From the point of view of the Federal Environment Agency, this runs counter to the climate goals. The UBA writes: “The forest should be preserved as a carbon sink and this output should be maximized as far as possible. To do this, even less carbon may be removed than is bound. The climate-friendly potential is therefore limited, so it is not advisable to use wood for energy for climate protection reasons.”
Firewood industry believes criticism is unjustified
Gerd Müller, head of the office of the Federal Association of Firewood Trade and Firewood Production, considers the criticism of heating with wood to be unjustified. “We can only deliver as much wood as the forest can bear and we stick to that.” Around 100 companies that process or produce firewood belong to the association. Müller emphasizes that sustainable forest management is practiced in Germany. Accordingly, no more trees would be harvested than could grow back. That is why it is currently not possible to meet the high demand for wood.
According to the German Pellet Institute, which belongs to the German Energy Wood and Pellet Association, around 32,000 pellet heating systems were sold in the first half of this year – twelve percent more than in the same period last year. But the prices for firewood and wood pellets for stoves and heating systems are also rising sharply: in August they were almost 86 percent higher than in the same month last year, as the Federal Statistical Office announced in September. Overall consumer prices rose by 7.9 percent over the same period. The statisticians explained that the reasons for the well above-average price increase were not only the increased demand but also the higher procurement and transport costs in the timber industry.
According to the Pellet Institute and the Federal Association for Firewood Trade and Firewood Production, heating with wood is still cheaper than with oil or gas. According to the Pellet Institute, a kilowatt hour generated by burning wood pellets cost an average of around 8.8 cents in the period from January to August – with natural gas around 14.11 cents.
European Parliament decides restrictions
It was only in mid-September that the European Parliament voted to reduce the amount of wood that can be used to generate energy in the future and to limit financial support from the state. However, wood burning should continue to be considered a renewable energy source.
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