With concerns regarding energy supplies, many are turning to wood as a fuel. However, media reports have created a negative image of the energetic use of wood. Do you need to suffer from a guilty conscience when heating with firewood?
The Bavarian State Institute of Forestry (LWF) examines the points of criticism in this article and provides real data and facts.
Regarding particulate matter (i.e., suspended particulate matter with a diameter of <2.5 µm), it should be noted that from 1995 to 2020, total particulate matter emissions decreased by 60%, and by 47% from households and small-scale consumers. Therefore, the air is becoming cleaner. However, air quality standards have become increasingly stringent.
Wood-burning stoves in Germany account for almost a fifth of fine dust emissions. These primarily result from single-chamber firewood stoves, where operational errors are technically difficult to avoid. In modern central heating boilers using pellets or wood chips, fine dust emissions are almost non-existent.
Burning firewood is climate-neutral
Emissions per kilowatt-hour of heat for all three types of wood combustion (roundwood, wood chips, pellets) are in the same range as solar energy and are significantly lower than those from oil or natural gas, as well as when compared to heat pumps. Emissions occurring in the upstream chain, i.e., during logging, transport, and processing, are also attributed to wood combustion. As long as the carbon stock in the forest does not decrease but remains stable or continues to increase as before, CO₂ emissions from wood combustion do not affect the climate balance.
The Bavarian State Institute of Forestry reveals that there is a growing belief that fine dust emissions resulting from wood combustion are not only harmful to health but also damaging to the climate. In reality, particulate matter often has a direct cooling effect on the climate.
Efficiency of wood fuel
Critics of using wood for energy argue that CO₂ emissions per unit of energy from burning wood exceed those from fossil fuels.
Admittedly, burning natural gas and liquid fuels releases less CO₂ per unit of energy produced than burning wood. However, carbon obtained from fossil sources, which has been stored in the ground for millions of years, also enters the atmospheric and biosphere carbon cycle, increasing it further. This is almost impossible to reverse. Thus, fossil fuels exacerbate the CO₂ problem, while wood does not.
Therefore, as long as the carbon stored in the forest does not decrease, timber harvesting and, consequently, the use of wood for energy are climate-neutral.
The time effect in the fight against climate change
Climate experts believe the coming years will be decisive for achieving climate goals. It is important to reduce CO₂ emissions immediately. Critics of using wood for energy argue that to obtain the same amount of energy, it would be better to emit a slightly smaller amount of carbon dioxide from fossil sources into the atmosphere rather than a slightly larger amount from the biosphere. Thus, there is a view that the volume of timber growing in the forest should be left as it is and that fossil fuels should be used instead. Such considerations are justified in the short term, but only if the CO₂ actually remains in the forest.
However, it should not be forgotten that deadwood, as well as harvesting residues left in the forest, are largely broken down again by microorganisms. As a result, the CO₂ initially sequestered in the wood is released again. Even a complete abandonment of wood use would not yield positive results. The consequence would be that wood products would also have to be replaced with other materials, and this, in turn, would usually involve significantly higher fossil fuel consumption.
Positive impacts on the forest's carbon store from ceasing operations would only be expected if it were possible to expand this store. However, according to LWF experts, this possibility is unrealistic.
Compensating forest stocks by replacing energy sources
Another argument against energy from wood is that increasing the forest's carbon dioxide storage potential binds more CO₂ than is achieved by replacing fossil fuels. However, scientists from the LWF believe that this argument overestimates the potential for further storage and the resulting additional CO₂ sequestration in forests.
In individual forest stands, it is possible to accumulate even more than 1000 m³ of wood per hectare, but not across landscapes or on a national scale. There are forest stands of all ages in the country; therefore, on average, the timber volume in stands is significantly lower.
Bavarian scientists assume that the maximum attainable timber stocks at the so-called “landscape level” are approximately 400 m³ per hectare. According to FAO (2015) data, there are only nine countries in the world where forest timber stocks exceed 300 m³ per hectare, and Germany is among them.
In a study conducted by Knoke (1998) in 13 Bavarian state forest trial areas, it was found that the stand volume was 408 m³ per hectare. This result is also confirmed by a study conducted by Schulze et al. (2022) Schulze et al.. They evaluated inventory data from several hundred forest stands and determined average volumes slightly above 400 m³, which also included deadwood stocks. According to the 2012 National Forest Inventory (BWI 2012), timber stocks in Bavarian forests were 396 m³/ha, which is very close to the real 400 m³/ha limit.
However, under Section 3a of the Climate Protection Act, the federal government decided to further increase the volume of forest CO₂ sinks. By 2045, a storage capacity of 40 million tonnes of carbon dioxide equivalent must be reached, i.e., 2.4 times more than in 2020. Nevertheless, in the 2021 climate protection report, the federal government writes: “According to forecasts, the sequestration capacity of forests could increase due to the age structure of forest stands and weather-related forest damage, as well as due to changes resulting from decreased wood usage.” Thus, the discrepancy between intentions and reality is well known.
The relationship between climate protection and nature conservation
There are calls to stop managing large forest areas and instead use them for nature conservation (in accordance with the National Biodiversity Strategy and the EU Biodiversity Strategy). To make this goal easier to achieve, nature conservation interests are often combined with climate protection interests. The federal government’s action programme “Natural Climate Protection” speaks of synergies between climate protection and nature conservation, thus emphasising the coherence of these interests. For example, it is claimed that unmanaged forests will store more carbon.
The study by Schulze et al. (2022) does not support this thesis. When comparing stocks (including deadwood) in unmanaged forest stands with managed ones, no significant differences were found in living and deadwood biomass stocks for coniferous stands. In the case of deciduous forests, however, the CO₂ stocks in unmanaged forests were slightly higher.
In both cases, however, wood increment was significantly higher in managed stands – the expected CO₂ sequestration effect in unmanaged stands is, at the very least, questionable. Furthermore, as already pointed out, forest CO₂ stocks in Bavaria have almost reached their maximum.
“Climate washing”
“Climate washing” is the embellishment of climate balance sheets. In the United Nations Framework Convention on Climate Change, the world's countries have agreed to establish greenhouse gas balances separately by sector and by country (source and territorial principle). The EU regulation governing European reporting (the so-called Monitoring Regulation) states: “The emission factor for biomass is zero.” This assertion led some European countries, especially coastal ones, to convert their coal-fired power plants to pellets and import pellets from abroad.
This relieves the energy sector by balancing out fossil fuel CO₂ emissions. The impact on forest carbon stocks caused by using pellets does not need to be accounted for. This happens at the expense of the supplying countries. These countries, when balancing their LULUCF sector (Land Use, Land-Use Change and Forestry), would have to include the impact that pellet supplies have on forest CO₂ stocks. However, many scientists are concerned that supplying countries are incorrectly balancing their carbon stocks in forests. In Germany, conversely, pellets are usually produced from wood residues that arise when processing raw timber for products intended for material use. Science does not criticise this procedure. Germany is self-sufficient in pellets; in 2021, even 431,000 tonnes of wood pellets were exported. Therefore, accusations against Germany of “climate washing” would be unfounded.
Cascading use
Another objection to the use of wood for energy is that wood is a scarce raw material. If wood were used as a material, the sequestered carbon would remain in wood products for longer. Also, replacing energy-intensive products, such as steel or bricks, with wood products helps save fossil energy (material substitution). All these arguments are correct. However, not all wood or its components are suitable for material use. In such cases, local energy use of a relatively small volume of wood is more sensible than transporting it over long distances to remote factories.
Wood is stored energy
When comparing wood with other renewable energy sources, it is often overlooked that wood can also be valued as stored energy that can be used at any time. Electricity produced by wind or photovoltaics must first be stored in batteries, moved to storage tanks, or used for hydrogen production if it is not used immediately. In all cases, this leads to significant conversion losses.
Wood is a local and therefore crisis-proof energy resource
Russia's war against Ukraine shows the extent to which Germany is dependent on other countries for fossil fuels. These countries are often not governed democratically and are prepared to use their resources as leverage to defend their political interests. It is understandable that citizens, worried about heating supplies for the coming winter, are increasingly switching to wood energy. Although the prices of some wood fuel types have also risen in recent years – even sharply in the last months – they remain much less volatile and unstable than oil prices.
Moreover, wood energy can be purchased in a decentralised manner from regional suppliers, and there is the option to do some of the work yourself, such as through self-service arrangements. Thus, wood energy is relatively cheap and acts as an alternative to other energy resources, especially for households with low incomes or in structurally weak regions.
Summary: “When heating with firewood, your conscience is clear!”
The energetic use of wood is criticised and triggers discussion. The contribution from LWF scientists examines the points of criticism regarding the energetic use of wood and presents the true facts. On the one hand, the authors name ways to largely avoid fine dust emissions generated by burning wood. On the other hand, they compare the energetic use of wood with burning fossil fuels and compare their impacts on the climate. Furthermore, the authors explain how they evaluate the carbon dioxide storage potential in forest stocks, assessing the possibilities and impacts.
Scientists concluded that the energetic use of wood does not cause any guilty conscience, provided that it takes place within the specified framework.