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The sustainable production of biomass for energy must play a key role in the world’s future climate-friendly energy system.
A recent report published by the Joint Research Centre of the European Commission on the use of woody biomass for EU energy production called for an honest discussion to “detoxify the debate surrounding the sustainability of wood-based bioenergy.”
It’s a very timely call. There are many opinions about the climate neutrality of biomass for energy purposes. Many opinions are influenced by subjective interpretations and special interests. When referencing scientific papers, facts are often repeated out of context.
When considering climate-friendly options for our future energy system, the debate must be much more nuanced than only considering if something is green or not.
Simply put, burning biomass (plant matter) produces heat and can also be used to generate electricity or to produce biofuels. Generally speaking we know this as bioenergy. This includes agricultural residues as sugarcane bagasse and corn cobs, wood chips and pellets from thinnings and wood industry residues, and even dried animal dung. As organic material, they all contain stored energy absorbed naturally from the sun.
Bioenergy is often pitched as a trendy solution to our energy needs, but it’s a concept that stretches back beyond any other derived energy source, when our cave-dwelling ancestors burned firewood to keep warm.
The European Academies Science Advisory Council (EASAC) is among the leading voices to claim that using biomass for energy is bad for the climate. But that paints a far too simplistic picture. When considering the overall carbon balance between earth and its atmosphere, a different picture emerges.
A common criticism of biomass combustion is that the CO2 emissions have the same global warming effect as CO2 released from the combustion of fossil fuels.
IEA Bioenergy explained why this is not a fair comparison: “Burning biomass for energy emits carbon that is part of the continuous exchange of carbon between the biosphere and the atmosphere. In contrast, fossil fuel emissions represent a linear flow of carbon from geological stores to the atmosphere. Therefore, the effect on the atmospheric GHG concentrations of switching from fossil fuels to biomass cannot be determined by comparing CO2 emissions at the point of combustion.”
Øyvind Skreiberg, chief scientist at SINTEF Energy Research, explains that there is a fixed sum of carbon stock on Earth and its atmosphere: “Global warming is a result of a shift of more carbon to the atmosphere, mainly as CO2. If the fixed carbon stock embedded in biomass remains constant, there is no net global warming from biomass combustion because there is no net addition of CO2 to the atmosphere.”
In its revised renewable energy directive, the EU defined direct CO2 emissions from biomass as climate neutral in the energy sector. Any non-neutrality in either direction is accounted for through changes in the carbon stock embedded in biomass and reported in the land use sector. “This means it is only an increased net use of biomass that can lead to increased direct CO2 emissions and with that net global warming. If the use of biomass stabilizes at a higher level, then a new equilibrium will be reached between the carbon stock in biomass on Earth and in the atmosphere,” says Skreiberg.
One of the biggest arguments from EASAC and the JRC is related to forest conservation. While the destruction of rainforest is a major issue in some parts of the world, the notion that deforestation is occurring all over the world is not the case. In Norway and large parts of Europe, forest biomass stock is increasing.
A 2017 paper published in the journal Biofuels, Bioproducts and Biorefining disputed the assumption that more use of biomass for energy would cause deforestation: “Projections show that in the absence of additional demand for wood pellets, natural timberland area is projected to decline by 450–15,000 km2 by 2030. Under the high wood pellet demand scenario, more (2,000–7,500 km2) natural timberland area is retained and more (8,000–20,000 km2) pine plantation is established.”
Professor Francesco Cherubini, director of the Industrial Ecology program at Norway’s NTNU university, explains that active forest management secures forests as carbon sinks and not carbon sources: “Well managed areas of timberland and forest contribute to the increasing forest carbon stock while providing biomass for multiple purposes, including energy.”
Of course, the availability of land and possibilities for beneficial land use changes are important considerations when evaluating biomass potential and climate impacts. But this is about more than the amount of available land. Once again, it is difficult to talk about the biomass stock in isolation. The climate, biomass diversity impacts and the opportunity cost of the land must also be considered.
Such discussion also raises big questions about the food systems of today. “Nearly half the planet’s land is used to feed animals, not people. For example, soybean growth is the main driver for the deforestation of the Amazon, but more than three-quarters of the crop is used to feed animals,” says Cherubini.
“Bioenergy must sit alongside other climate change mitigation options to achieve the Paris climate goals. We shouldn’t think of this as a competition between using available land to expand forests and growing crops for energy. We need both,” he adds.
Regardless of direct CO2 emission mitigation, the emission of a fossil-sourced CO2 molecule must be compensated for by an increase in the Earth’s non-fossil-based carbon stock or other ways of removing CO2 from the biosphere, if the carbon balance between the Earth and its atmosphere is to be maintained. But there is a limit on how much carbon can be naturally absorbed by the oceans and the terrestrial biosphere, and current emission levels are well beyond the natural sink capacity.
That balance is not maintained today, to the point where the carbon stock in the atmosphere becomes critical with respect to limiting average global temperature rise.
This means labelling bioenergy as “bad” is misleading. Limiting the impact of climate change requires a tremendous effort including an aggressive reduction of fossil emissions. Bioenergy alone will not solve the climate crisis, but it will play a crucial role as part of wider change. “We need integrated and multiple solutions, which include forest management, forest expansion, and forest conservation, together with parallel improvements in the agri-food sector,” says Cherubini.
Given the need to reduce fossil emissions, carbon capture and storage (CCS) technologies can be used in conjunction with bioenergy to create a carbon negative solution. According to the IPCC this process alone has the potential to permanently store gigatons of CO2 every year, although this is reliant on sustainable biomass availability and the full-scale implementation of CCS.
There are many more biomass-based climate positive solutions beyond combustion that can make a contribution to the energy transition.
Storing charcoal in the soil improves soil quality while creating a carbon sink, an option for cities as well as rural areas. An increased use of wood as a building material will also store carbon for the long-term.
We need a portfolio of sustainable options that consider complex local contexts and greater societal needs for material and energy.
So as IEA stated recently, let’s not take the concept of woody biomass off the table. Instead, our focus should be on ensuring the best possible management practices and regulations are developed for sustainable production.