Yes, biomass produces greenhouse gases at every stage of its lifecycle, from growing and harvesting to processing, transporting, and burning. Burning wood, for example, releases more carbon dioxide per unit of electricity than burning coal. The claim that biomass is “carbon neutral” rests on the idea that regrowing plants will reabsorb that carbon, but the timeline for that reabsorption is hotly debated and can stretch from decades to centuries.
What Burning Biomass Releases
When biomass burns, it releases carbon dioxide, methane, nitrous oxide, and particulate matter. The carbon dioxide output is substantial. Data from the Drax power station in the UK, one of the world’s largest biomass electricity plants, showed that burning wood pellets produced about 965 grams of CO2 per kilowatt-hour of electricity. Coal burned in the same facility produced 856 g CO2/kWh. That means the biomass actually released roughly 13% more CO2 per unit of energy than coal did at the smokestack.
This isn’t a fluke of one power station. The Schiller power station in New Hampshire reported 1,444 g CO2/kWh from its wood boiler, compared to 1,243 g CO2/kWh from its coal boilers. Biomass is less energy-dense than fossil fuels, so you need to burn more of it to get the same amount of electricity, which means more CO2 per kilowatt-hour at the point of combustion.
Beyond CO2, biomass combustion also produces black carbon, a form of soot that absorbs sunlight and warms the atmosphere. Research on smoke from biomass fires found that black carbon deposition alone can produce a radiative forcing (a measure of warming effect) ranging from +0.1 to +3.2 watts per square meter in affected areas, while also darkening snow and ice surfaces and accelerating their melting.
Emissions From Decomposition
Biomass doesn’t have to burn to emit greenhouse gases. When organic material decomposes, it releases both CO2 and methane. The type of decomposition matters enormously. In oxygen-rich environments like compost piles, CO2 dominates. In oxygen-poor environments like landfills or waterlogged soil, bacteria produce methane, which traps about 80 times more heat than CO2 over a 20-year period.
Composting data illustrates the scale. For yard waste composted in open air, the mean emission is about 171 grams of CO2 per kilogram of wet material, plus roughly 2 grams of methane. That methane fraction sounds small, but its outsized warming potential makes it significant. Landfilling the same organic waste produces even higher total greenhouse gas emissions than composting, a finding that reflects broad consensus in the research community.
Methane Leaks From Biogas Plants
Biogas facilities capture methane from decomposing biomass and burn it for energy, which is supposed to prevent that methane from reaching the atmosphere. In practice, these plants leak. A large-scale assessment of anaerobic digestion facilities found that methane losses vary widely depending on plant size, design, and the type of material being processed.
Wastewater treatment plants had the highest average methane losses at 7.0% of all methane produced. Manure-based plants lost 3.7%, biowaste facilities lost 2.8%, and energy crop plants lost 1.9%. Plant size also mattered: small and medium facilities leaked an average of 5.6% of their methane, while larger plants with sealed storage tanks kept losses to about 2.2%. Since the entire climate benefit of biogas depends on capturing methane rather than venting it, these leakage rates can significantly erode or even eliminate the advantage over fossil fuels.
The Full Supply Chain
Combustion emissions are only part of the picture. Growing, harvesting, drying, pelletizing, and shipping biomass all require energy, mostly from fossil fuels. One lifecycle analysis estimated that wood pellet supply chains add roughly 132 to 140 g CO2-equivalent per kilowatt-hour before the pellets are even burned. On top of that, storing wood chips and pellets at mills or power stations releases additional methane as the material partially decomposes, contributing an estimated 162 g CO2/MWh in extra emissions.
A separate lifecycle comparison found that biomass-derived hydrocarbon fuels produced between 2.87 and 3.29 kg of CO2-equivalent per functional unit, compared to 4.59 kg for the fossil-fuel equivalent. That’s a real reduction, roughly 28 to 37%, but it’s far from zero emissions and far from carbon neutral.
The Carbon Payback Problem
The argument for biomass as a climate-friendly fuel hinges on regrowth. Trees and crops absorb CO2 as they grow, so in theory, replanting after harvest should eventually recapture the carbon released during burning. The time this takes is called the carbon payback period, and it varies wildly.
A meta-analysis of 38 published studies on forest biomass carbon accounting found payback periods ranging from zero to 8,000 years. That enormous range reflects differences in forest type, climate, soil, and one especially important variable: wildfire. Studies that included wildfire risk in their models produced much longer and more variable payback periods, because fire can destroy regrowing forests before they’ve had a chance to reabsorb the carbon debt. In regions where wildfire is becoming more frequent due to climate change, the payback window keeps stretching further out.
Land Use Change Multiplies the Impact
When demand for biomass increases, it can trigger land use changes that release massive amounts of stored carbon. If forests are cleared to grow energy crops, or if existing farmland shifts to biomass production and food crops move onto newly cleared land elsewhere, the upfront carbon release can dwarf any annual savings from replacing fossil fuels.
One influential study estimated that biofuel production on converted land initially releases 17 to 420 times the greenhouse gas savings it provides on an annual basis. Another calculated that corn ethanol produced on land subject to indirect use changes would produce no net greenhouse gas benefit for the first 167 years. These figures are contested, and they depend heavily on assumptions about which land gets converted and how. But they illustrate that biomass energy can, under certain conditions, increase total greenhouse gas emissions for generations before any climate benefit materializes.
How Regulators Treat Biomass
Despite these complexities, many government frameworks count biomass as low-carbon or carbon neutral. The U.S. Renewable Fuel Standard, established by the Energy Independence and Security Act of 2007, sets volume targets for biofuels and requires the EPA to consider factors including climate change, air quality, and commodity prices when setting those targets. The EU’s renewable energy directives also include biomass, though with sustainability criteria that have tightened over time.
The gap between regulatory classification and atmospheric reality is where the controversy lives. At the smokestack, biomass emits more CO2 than coal. Across its lifecycle, it emits less than fossil fuels in many scenarios but more in others, depending on feedstock, supply chain efficiency, and whether the land and forests used can realistically regrow fast enough to close the carbon debt within a meaningful timeframe.