Why Burning Forests for Energy Might Be a Step Backward
The alarming science behind the world's "carbon neutral" energy source
In the global race to replace fossil fuels, many countries are turning to an ancient energy source: wood. Classified as "carbon neutral," burning forest biomass has become a multi-billion-dollar industry, accounting for 60% of the European Union's renewable energy mix 2 6 . Yet, a growing chorus of scientists warns this solution rests on a critical accounting error that may actually accelerate climate change and harm our forests. This is the serious, and ongoing, mismatch between science and policy in forest bioenergy.
of EU renewable energy comes from biomass
more CO₂ than coal per energy unit
of EU biomass comes from whole trees
Wood is less energy-dense than coal. Generating the same amount of electricity with wood can emit 18% more CO₂ than using coal 2 .
Replacing coal with forest biomass "increases greenhouse gas emissions for decades to centuries" 2 .
The biomass industry often argues that sustainably managed forests, where growth outpaces harvest, ensure carbon neutrality 6 . However, research shows this is a landscape-scale miscalculation. An undisturbed part of a forest is used to offset emissions from logged stands, creating an accounting trick that doesn't reflect atmospheric reality 2 .
Furthermore, the demand for wood pellets can lead to the direct harvesting of primary woody biomass—whole trees and trunks—which makes up about 37% of the wood burned for energy in the EU 2 . This practice not only creates a massive carbon debt but also reduces the planet's overall carbon sink capacity.
To understand the real impact of biomass energy, researchers use sophisticated simulation models that track carbon stocks and fluxes over time. These models combine forest inventory data with growth algorithms to project the long-term carbon consequences of different harvesting scenarios.
A 2021 Finnish study provides a perfect case study. Researchers created a mapping framework to investigate how harvesting forest residues for bioenergy affects carbon dynamics in a boreal landscape 8 .
The team gathered extensive forest inventory data across a southern boreal landscape in Finland, detailing tree species, age, density, and soil types 8 .
They used the MOTTI stand simulator to project forest growth, timber yield, and carbon stored in biomass. The Yasso15 model was used to simulate carbon changes in litter and soil 8 .
The researchers ran simulations under different management regimes, including standard harvesting and intensive residue extraction (removing branches, tops, and stumps) 8 .
Stand-level results were scaled up to the entire landscape using the inventory data, creating fine-resolution maps of carbon stock changes over a century (2012–2100) 8 .
The study found that regular harvesting was a key driver of carbon stock changes at the landscape level. More importantly, it quantified the specific cost of residue extraction:
Removing harvest residues caused significant carbon loss from litter and soil, particularly when both aboveground residues and stumps were harvested 8 .
This practice also reduced annual coarse woody litter production, a key indicator for deadwood abundance. This has clear negative impacts for the countless deadwood-dependent species that are crucial for forest health 8 .
The experiment concluded that while bioenergy reduces fossil fuel emissions, these gains are partly counteracted by the reduction in forest carbon stocks 8 . This crucial trade-off is often ignored in policy decisions.
A summary of findings from the EU's Joint Research Centre report on how long it takes for different types of woody biomass to provide a net climate benefit compared to fossil fuels 2 .
| Biomass Feedstock | Description | Estimated Carbon Payback Period |
|---|---|---|
| Primary Woody Biomass | Tree trunks and stems | At least 2 decades, often much longer |
| Forest Harvest Residues | Branches, tops, and small branches (slash) | 1-2 decades |
| Secondary Residues | By-products from sawmills and pulp mills | Immediate or very short |
Data from a 2017 study on bioenergy potential shows the variation in energy content within a single tree, highlighting why certain parts are targeted for pellet production 4 .
| Tree Species | Stem Wood (kcal/kg) | Bark (kcal/kg) | Foliage/Needles (kcal/kg) | Branches (kcal/kg) |
|---|---|---|---|---|
| Pine | 4,870 | 4,887 | 5,148 | 4,990 |
| Spruce | 4,830 | 4,829 | 5,108 | 4,927 |
| Birch | 4,762 | 4,672 | 4,503 | 4,995 |
This data helps visualize what is lost when a whole tree is harvested. Note that "stems" are used for traditional timber, while other components are often diverted to bioenergy 4 .
To build this compelling case, scientists rely on a suite of complex models and data sources.
Extensive, nationally collected data on forest structure and composition form the foundational reality against which models are run 8 .
These models simulate the growth of individual forest stands over time, projecting tree growth, mortality, and carbon accumulation in biomass under different management scenarios 8 .
A specialized model for simulating the decomposition of organic matter and the dynamics of carbon storage in forest soils, which is critical for understanding the full carbon impact of residue harvesting 8 .
A methodology used to evaluate the total environmental footprint of a product or activity—in this case, biomass energy—from harvest to combustion, providing a more complete picture than smokestack emissions alone 2 .
The scientific evidence has led hundreds of experts to speak out. In 2018, 772 scientists, including a former chief scientist for the UK government, signed a letter to the European Parliament urging reforms to bioenergy policy 2 . In 2021, another 500 scientists followed suit, asking world leaders to end subsidies for burning wood 6 .
Requiring emissions from biomass combustion to be counted in the energy sector, creating a transparent and honest ledger 6 .
The science is clear. As one major paper concluded, "Serious mismatches continue between science and policy in forest bioenergy" 5 . Bridging this gap is not just an academic exercise; it is essential for making the right choices in our fight against climate change. The danger is that by the time the policy world acknowledges the carbon debt from today's biomass energy, it will be too late to repay it.