Does wood bioenergy help or harm the climate?

Figures & data

Table 1. Claims made about bioenergy and facts that counter those claims

Claim: To stop climate change, it is necessary to replace fossil fuels with renewable energy, including wood bioenergy. “Well, that’s the prime objective, to go to full renewables. But simply looking at how fast we need to do that, we just can’t reach the levels of renewables we would need to have [to stop burning fossil fuels and meet European Union energy needs] to completely exclude biomass.” Frans Timmermans, Vice President, European Commission, speaking at the 2021 UN Climate Summit, Glasgow (COP 26) (Catanoso 2021).	Fact: To stop climate change, greenhouse gas emissions including carbon dioxide must drop rapidly, reach net zero by approximately 2050 and be net negative after that. Burning wood for bioenergy emits carbon dioxide. Trees harvested for bioenergy may regrow, but regrowth is not certain and even if it occurs, would not remove the excess carbon dioxide from burning wood for many decades to a century or longer. In the meantime, the excess carbon dioxide remains in the atmosphere and worsens global warming. To meet our climate goals, steep carbon dioxide emission cuts from all sources are needed now (IPCC 2022; IPCC 2021).
Claim: Wood bioenergy only adds carbon that was recently taken up by trees back to the atmosphere. “While burning fossil fuels releases CO2 that has been locked up for millions of years, burning biomass simply returns to the atmosphere the CO2 that was absorbed as the plants grew.” UN Food and Agriculture Organization (Matthews and Robertson 2001)	Fact: A molecule of carbon dioxide added to the atmosphere causes the same global warming whether it came from fossil fuels, trees, or other plants. “burning biomass for energy provision increases the amount of carbon in the air just like burning coal, oil or gas if harvesting the biomass decreases the amount of carbon stored in plants and soils, or reduces carbon sequestration.” The result is a “fundamental accounting error” that “will likely have substantial adverse consequences” (Haberl et al. 2012).
Claim: Wood bioenergy is carbon neutral. Carbon that is emitted now and reabsorbed later has no impact on the climate. “Jen Jenkins, vice president at Enviva, the world’s largest pellet producer, said her industry helped solve the climate crisis: The pellets displace coal, and even though their combustion releases carbon emissions, those would be sucked out of the atmosphere by replanted trees” (Ouzts 2019).	Fact: Eventual carbon neutrality is not climate neutrality. The climate damage caused by adding carbon dioxide to the atmosphere when wood is burned is not reversed even if forest regrowth eventually removes that carbon dioxide. Even if trees grow back, the additional warming creates irreversible changes: the Greenland and Antarctica ice sheets will not return, sea level will not drop, and thawing permafrost will have released more methane. These changes are not undone even if trees grow back (Solomon et al. 2009, Sterman, Siegel, and Rooney-Varga 2018b, IPCC 2022).
Claim: If trees are burned at the same rate that the forest grows, the amount of carbon stored in the forest remains constant. Therefore, wood bioenergy is carbon neutral. “In the Southeast U.S., privately owned and well managed forests produce one-fifth of the world’s wood products. And even as they produce these harvested wood products, forests in the region are adding more carbon.” (Enviva n.d.) “ … the carbon neutrality of biomass harvested from sustainably managed forests has been recognized repeatedly by numerous studies, agencies, institutions, and rules around the world … .” US Senator Susan Collins (R, Maine) on the amendment to the Energy Policy Modernization Act, S. 2102 in 2016. “We are enormously grateful to … all co-sponsors of this amendment, which accurately reflects the carbon beneficial impacts of power from forest biomass,” Bob Cleaves, President and CEO of Biomass Power Association (Voegele 2016).	Fact: Growing use of wood bioenergy removes carbon from existing forests and emits it as carbon dioxide into the atmosphere. The stock of carbon on the land immediately falls. If wood for bioenergy is harvested at a constant rate and the land is replanted and allowed to regrow, regrowth may eventually equal the harvest. Until then, carbon removal exceeds carbon sequestration, causing the stock of carbon on the land to fall. If the carbon added from regrowth eventually equals the carbon removed by harvest and other losses, then the stock of carbon in the forests would stabilize and the harvest might be deemed “sustainable.” But the total stock of carbon on the land stabilizes at a level lower than before wood bioenergy use began. The carbon lost from the land is added to the atmosphere, worsening climate change (Sterman, Siegel, and Rooney-Varga 2018a; Sterman, Siegel, and Rooney-Varga 2018b). When wood is taken from growing forests, the carbon that those growing trees would have removed from the atmosphere is also lost. And if bioenergy harvest grows over time, as projected, then emissions will exceed regrowth every year, even if replanting equals the harvest every year (Sterman, Siegel, and Rooney-Varga 2018a).
Claim: New trees will be planted that offset the carbon emitted from wood used for bioenergy. Dale Greene, dean of forestry at the University of Georgia, and an advisor to Drax (said) “If we harvest more (for bioenergy), we plant more and there is more carbon in the forest” (Pearce 2020).	Fact: Regrowth is uncertain. Land harvested for bioenergy may be converted to other uses (pasture, cropland, development). Newly planted trees may be reharvested as soon as it is economically worthwhile to do so (Newman 1988), releasing the carbon they accumulated back into the atmosphere. The result is lower stocks of carbon on the land and more in the atmosphere, worsening climate change. Newly planted trees have a high mortality rate, contain very little carbon and do not accumulate much carbon for decades (Besnard et al. 2018; Stephenson et al. 2014). Fire, drought, extreme weather, insects, and disease would cause the carbon accumulating in forests harvested for bioenergy to return to the atmosphere, worsening climate change. Climate change increases these risks (Brecka, Shahi, and Chen 2018; Xu et al. 2019), making it less likely that forests will fully recover carbon lost.
Claim: Wood bioenergy is carbon neutral when waste wood, thinnings, and wood that is not suitable for timber are burned. “Wood biomass is sourced from industrial wood waste (like sawdust), or low-grade wood, including ‘thinnings,’ limbs, tops or crooked and knotted trees that would otherwise not get used for lumber or other higher-value products.” Seth Ginther, Executive Director, U.S. Industrial pellet Association (Booth 2018; Ginther 2018).	Fact: (i) Wood waste take years or decades to decompose, while burning it releases carbon immediately (Booth 2018). Allowing wood waste to decompose provides nutrients important for forest health. (ii) Much ‘waste wood’ unsuitable for lumber can be used in other long-lived wood-based products, like cellulose building insulation and oriented strand board keeping it out of the atmosphere for decades (Reuse Wood 2020).
Claim: Young trees grow faster than older trees. Therefore we should harvest older trees that are not accumulating much carbon, use them for bioenergy, and replace them with faster growing younger trees. “ … young forests grow rapidly, removing much more CO2 each year from the atmosphere than an older forest covering the same area” (NCASI 2021).	Fact: Harvesting and burning old trees releases large amounts of carbon immediately. The young trees that may grow if the land is reforested will not accumulate as much carbon as the existing forest emitted for a century or more. Older forests accumulate more carbon in trees and soils per year than do younger forests (Stephenson et al. 2014).
Claim: Forests that are growing today are removing carbon dioxide from the atmosphere, which makes wood bioenergy carbon neutral and justifies omitting the carbon dioxide from burning wood from carbon accounting. “ … since the state [North Carolina] has increasing overall timber volumes per acre and in total, we are sustainable, and we are carbon neutral or better” (Cubbage and Abt 2020). “The continued forest carbon gain across the landscape … means that products from the Southeast U.S., including wood bioenergy, are not adding carbon emissions to the atmosphere. As a result, when wood pellets from this region are used to generate energy, we can set stack emissions to zero.” (Enviva n.d.)	Fact: the carbon dioxide (“stack emissions”) from burning wood for energy does not instantly increase forest growth on the harvested land or in forests miles away. Whether forests are growing now at landscape scale is irrelevant. What counts is the incremental impact of bioenergy on atmospheric carbon dioxide and climate change, i.e., how the amount of carbon dioxide in the atmosphere is changed by using wood bioenergy. Burning wood for energy emits carbon dioxide, increasing the amount of carbon dioxide in the atmosphere above what it would have been, even if the wood displaces coal or other fossil fuels (Sterman, Siegel, and Rooney-Varga 2018a). Harvesting wood from forests that are growing also prevents the growth of the forests that would have occurred but for harvesting and burning that wood. The faster the forests harvested for bioenergy are growing, the worse the climate impact of bioenergy (Sterman, Siegel, and Rooney-Varga 2018b).

Figure 1. Life cycle emissions from wood bioenergy. Every stage of the supply chain adds carbon dioxide to the atmosphere, from cutting the trees through transport, processing the wood into chips or pellets, transporting them to a power plant, and combustion. Carbon dioxide is removed only later, and only if, the harvested land regrows. Photo credits, left to right: Power Plant, courtesy of Paul Glazzard, Creative Commons Attribution-ShareAlike 2.0 license. Transport: Handymax bulk carrier, courtesy of Nsandel/Wikimedia/Public Domain. Pellet mill, Truck Transport, and Forest images all courtesy of Dogwood Alliance, used with permission.

Figure 2. Impact of harvesting wood for bioenergy in 2025 from a 50-year-old oak-hickory forest in the south central USA. Top: Change in carbon on the harvested land (tons carbon per hectare). Brown: carbon in soils and dead organic matter; Green: carbon in living biomass. Dotted line: the total carbon stock (living biomass and soils) if the forest were not harvested in 2025. The forest would have continued to grow and remove carbon from the atmosphere but for being cut for bioenergy. The difference between the dotted no-harvest line and the top of the green band is the carbon emitted into the atmosphere by the harvest. Bottom: Change in atmospheric carbon dioxide resulting from the harvest and combustion of the wood. Solid line: wood displaces a zero-carbon energy source. Dotted line: wood displaces coal. Scale: the initial rise in atmospheric carbon dioxide when wood displaces zero-carbon energy is normalized to 100 percent. The initial rise in atmospheric carbon dioxide when wood displaces coal is about 50 percent less due to the emissions avoided by the reduction in coal use.

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