Report from the Woodwell Climate Research Center
As more and more countries adopt climate targets to achieve net zero greenhouse gas emissions, the relevance of forests as stores of sequestered carbon has increased. However, the growing use of forest biomass to generate electricity and heat has raised concerns over the immediate emissions resulting from burning wood.
Many national and intergovernmental policy frameworks, including those of the EU and UK, currently treat biomass energy as zero-carbon at the point of combustion. Accordingly, they grant it access to financial and regulatory support available for other renewable energy sources. These incentives have driven a rapid increase in the consumption of biomass for energy, even though its combustion may increase atmospheric concentrations of carbon dioxide (CO2) for years or even decades to come.
This report examines the issue in relation to one particular source of woody biomass: wood pellets sourced from the US that are burnt for electricity and combined heat and power (CHP) in the EU and UK. Although wood pellets represent only a proportion of the total woody biomass consumed for energy in the EU – and of forest harvests in the US – the market has grown rapidly in recent years. US-sourced pellets account for the majority of wood pellet imports to the UK and are an important source for the EU.
In 2019, according to our analysis, US-sourced pellets burnt for energy in the UK were responsible for 13 million–16 million tonnes of CO2 emissions, when taking into account emissions from their combustion and their supply chain, forgone removals of CO2 from the atmosphere due to the harvest of live trees and emissions from the decay of roots and unused logging residues left in the forest after harvest. Almost none of these emissions are included in the UK’s national greenhouse gas inventory; if they were, this would have added between 22 and 27 per cent to the emissions from total UK electricity generation, or 2.8–3.6 per cent of total UK greenhouse gas emissions in 2019. This volume is equivalent to the annual greenhouse gas emissions from 6 million to 7 million passenger vehicles.
Emissions from US-sourced biomass burnt in the UK are projected to rise to 17 million–20 million tonnes of CO2 a year by 2025. This represents 4.4–5.1 per cent of the average annual greenhouse gas emissions target in the UK’s fourth carbon budget (which covers the period 2023–27), making it more difficult to hit a target which the government is currently not on track to achieve in any case.
(2021) Greenhouse gas emissions from burning US-sourced woody biomass in the EU and UK.pdf
By Tara W. Hudiburg et al
Atmospheric greenhouse gases (GHGs) must be reduced to avoid an unsustainable climate. Because carbon dioxide is removed from the atmosphere and sequestered in forests and wood products, mitigation strategies to sustain and increase forest carbon sequestration are being developed. These strategies require full accounting of forest sector GHG budgets. Here, we describe a rigorous approach using over one million observations from forest inventory data and a regionally calibrated life-cycle assessment for calculating cradle-to-grave forest sector emissions and sequestration. We find that Western US forests are net sinks because there is a positive net balance of forest carbon uptake exceeding losses due to harvesting, wood product use, and combustion by wildfire. However, over 100 years of wood product usage is reducing the potential annual sink by an average of 21%, suggesting forest carbon storage can become more effective in climate mitigation through reduction in harvest, longer rotations, or more efficient wood product usage. Of the ∼10 700 million metric tonnes of carbon dioxide equivalents removed from west coast forests since 1900, 81% of it has been returned to the atmosphere or deposited in landfills. Moreover, state and federal reporting have erroneously excluded some product-related emissions, resulting in 25%–55% underestimation of state total CO2 emissions. For states seeking to reach GHG reduction mandates by 2030, it is important that state CO2 budgets are effectively determined or claimed reductions will be insufficient to mitigate climate change.
(2019) Meeting GHG reduction targets requires accounting for all forest sector emissions.pdf
Report from the Dogwood Alliance, Natural Resources Defence Council and Southern Environmental Law Centre.
Global demand for wood pellets is devastating forest ecosystems in the Southeast United States. Investigations by media and independent watchdogs over the past decade reveal the truth about the supply chains for pellets exported by Enviva, the world’s largest wood pellet manufacturer. These investigations expose the damaging logging practices used to source the so- called biomass industry, including the clearcutting of iconic wetland forests. Enviva’s pellets from these ravaged forests are then shipped to utilities, such as Drax Power in the United Kingdom and Ørsted in Denmark.
Despite the claims of the industry, the independent reporting shows a disturbing pattern: wood pellets burned by Drax and others come from wood that is harvested from native hardwood forests in an area designated as a global biodiversity hotspot. They also spotlight the vast quantities of whole trees and other large-diameter wood— biomass feedstocks known to be high-carbon—that are entering Enviva’s supply chain.
Not only is this devastating for these irreplaceable forests, but it’s worsening our Earth’s climate crisis. Multiple independent, peer-reviewed studies have determined that burning biomass from forests for electricity creates more carbon dioxide emissions than burning coal, and that increased carbon dioxide concentrations persist in the atmosphere for decades or more.
Two recent investigations add new evidence about the destructive logging practices being used to provide biomass to Enviva, adding insult to injury in a region that’s suffered years of unsustainable logging. In March 2019, investigators in North Carolina again tracked logging trucks from a mature hardwood forest to Enviva’s Northampton wood pellet mill. In January 2018, reporters from the UK Channel 4 News program Dispatches traveled to North Carolina to examine what is happening on the ground in the forests that have become ground zero for feeding Drax Power Station’s voracious demand for wood. The images from the Dispatches investigation tell a story of ecological devastation in the name of clean energy: a once majestic wetland forest clearcut to supply wood to Enviva, and ultimately to Drax.
(2019) Global Markets for Biomass Energy are Devastating US Forests.pdf
By Beverly E. Law et al
Strategies to mitigate carbon dioxide emissions through forestry activities have been proposed, but ecosystem process-based integration of climate change, enhanced CO2, disturbance from fire, and management actions at regional scales are extremely limited. Here, we examine the relative merits of afforestation, reforestation, management changes, and harvest residue bioenergy use in the Pacific Northwest. This region represents some of the highest carbon density forests in the world, which can store carbon in trees for 800 y or more. Oregon’s net ecosystem carbon balance (NECB) was equivalent to 72% of total emissions in 2011–2015. By 2100, simulations show increased net carbon uptake with little change in wildfires. Reforestation, afforestation, lengthened harvest cycles on private lands, and restricting harvest on public lands increase NECB 56% by 2100, with the latter two actions contributing the most. Resultant co-benefits included water availability and biodiversity, primarily from increased forest area, age, and species diversity. Converting 127,000 ha of irrigated grass crops to native forests could decrease irrigation demand by 233 billion cubic metres·per year. Utilizing harvest residues for bioenergy production instead of leaving them in forests to decompose increased emissions in the short- term (50 y), reducing mitigation effectiveness. Increasing forest carbon on public lands reduced emissions compared with storage in wood products because the residence time is more than twice that of wood products. Hence, temperate forests with high carbon densities and lower vulnerability to mortality have substantial potential for reducing forest sector emissions. Our analysis framework provides a template for assessments in other temperate regions.
(2018) Land use strategies to mitigate climate change in carbon dense temperate forests.pdf
By John Sterman et al
Bioenergy is booming as nations seek to cut their greenhouse gas emissions. The European Union declared biofuels to be carbon-neutral, triggering a surge in wood use. But do biofuels actually reduce emissions? A molecule of CO2 emitted today has the same impact on radiative forcing whether it comes from coal or biomass. Biofuels can only reduce atmospheric CO2 over time through post-harvest increases in net primary production (NPP). The climate impact of biofuels therefore depends on CO2 emissions from combustion of biofuels versus fossil fuels, the fate of the harvested land and dynamics of NPP. Here we develop a model for dynamic bioenergy lifecycle analysis. The model tracks carbon stocks and fluxes among the atmosphere, biomass, and soils, is extensible to multiple land types and regions, and runs in ≈1s, enabling rapid, interactive policy design and sensitivity testing. We simulate substitution of wood for coal in power generation, estimating the parameters governing NPP and other fluxes using data for forests in the eastern US and using published estimates for supply chain emissions. Because combustion and processing efficiencies for wood are less than coal, the immediate impact of substituting wood for coal is an increase in atmospheric CO2 relative to coal. The payback time for this carbon debt ranges from 44–104 years after clearcut, depending on forest type—assuming the land remains forest. Surprisingly, replanting hardwood forests with fast-growing pine plantations raises the CO2 impact of wood because the equilibrium carbon density of plantations is lower than natural forests. Further, projected growth in wood harvest for bioenergy would increase atmospheric CO2 for at least a century because new carbon debt continuously exceeds NPP. Assuming biofuels are carbon neutral may worsen irreversible impacts of climate change before benefits accrue. Instead, explicit dynamic models should be used to assess the climate impacts of biofuels.
(2018) Does replacing coal with wood lower CO 2 emissions? Dynamic lifecycle analysis of wood bioenergy.pdf