CAMBRIDGE, Ma. - New research from MIT, Climate Interactive, and UMass Lowell has revealed that substituting coal with wood as a means to generate power could make climate change worse for many decades.
 
In a joint study, researchers found that wood pellets burned in European and U.K. power plants, such as a British Drax facility—which has transitioned some of its coal power generation capacity to wood pellets with the support of U.K. government subsidies—actually emit more CO2 per kilowatt hour than that generated by coal. Researchers say this is because wood is both less efficient at the point of combustion and has larger processing and supply chain emissions than coal.
 
Thus, using wood instead of coal in power generation increases the amount of CO2 in the atmosphere, worsening climate change until—and only if—the harvested forests regrow.
 

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Wood waste converted to jet fuel for cross-country flight

Alaska Airlines flew the first commercial flight using the world’s first renewable, alternative jet fuel made from wood waste and forest residuals.


U.S. forests are a main source for EU wood pellet imports, which have been rising as demand has grown. These forests grow back slowly, so it takes a long time to repay the initial "carbon debt" incurred by burning wood instead of coal, the researchers say. For forests in the central and eastern US, which supply much of the wood used in U.K. power plants, the payback time for this carbon debt ranges from 44 to 104 years, depending on forest type—and assuming the land remains forest. If the land is developed, or converted to agricultural use, then the carbon debt is never repaid and grows over time as the harvested land emits additional carbon from soils. 

"A molecule of CO2 emitted today has the same impact on the climate whether it comes from coal or biomass," says Prof. John Sterman. "Declaring that biofuels are carbon neutral, as the EU, UK and others have done, erroneously assumes forest regrowth happens quickly and fully offsets the emissions from biofuel production and combustion. One way to address the challenges raised in this study would be to count emissions where they occur, for example, at a power plant, and monitor and count carbon removed from the atmosphere by regrowth on the harvested land."

Since publishing this story yesterday, we've received comments taking issue with MIT's findings:

Benedict McAleenan, Head of Biomass UK, part of renewables body REA, said:

“It’s vitally important to understand how economics and science work together in the real world. In this study, there are highly unlikely scenarios being modeled, which results in worst-case conclusions.

“In the real world – as independently studied over several years by the UK government and others – responsible biomass sourcing is driven by a market that incentivizes best use of forest materials. It works as a hierarchy, with bioenergy at the bottom. This study unfortunately doesn’t model that accurately and jumps to the worst possible outcomes.

“Supplier forests in the Southern USA have actually doubled their inventories since the 1950s and we see roughly 1% net growth per year, supported by revenues from industries including bioenergy. In the EU, working forest inventories have grown 38% over the last 25 years or so.

“These are the real-world outcomes we’re achieving with the use of biomass – growing forests and a shift to reliable low-carbon electricity. It’s a real-world good news story for the environment.”

Andy Koss, Drax Power CEO said: “The MIT report uses unrealistic scenarios which do not take account of how we source our biomass in real life. The sustainable working forests we source from supply other industries – including construction and furniture making – with high-grade timber.  We take the low-grade material to make compressed wood pellets. This includes tree tops, limbs, sawmill residues, misshapen and diseased trees, as well as thinnings - small trees removed to maximise the growth of the forest. 

“Since Drax upgraded half of the power station to use biomass, those generating units deliver carbon savings of more than 80% compared to when they used coal. This takes account of our supply chain and is an independently audited figure.

“Since 1990 US forests have grown by 7.7 million ha and EU forests by 28 million ha thanks largely to sustainable demand for wood – as these forests grow they are absorbing carbon.

“Sustainable biomass is indispensable because it generates flexible renewable power at scale, and provides the full range of system support services National Grid expects to become increasingly important in keeping the lights on, as more intermittent renewables come online. Thermal power sources like biomass, gas and coal are the only technologies which can provide the full range of services to balance the grid and maintain secure supplies.”


Large biofuel and wood waste projects are in the works around the world. A $73 million synthetic fuel plant is being built in West Virginia, Canadian lumber giant Canfor is building its first biocrude oil plant in Vancouver, and Washington state-based Alaska Airlines made history flying the first commercial flight using the world’s first renewable, alternative jet fuel made from wood waste and forest residuals – limbs and branches left over after a harvest of a managed forest.

 
 
 

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