What can biofuels and biomaterials contribute to global carbon reduction? A lot depends on feedstock.
The IPCC’s latest report has one sobering takeaway: limiting warming to 1.5 degrees is now almost impossible.
Far from justifying climate fatalism, this conclusion only underlines the need for all economic sectors to lay out realistic mitigation strategies.
Biofuels and biomaterials are keystone climate mitigation technologies. A 2023 study estimated that if all plastics today were replaced with biobased ones, greenhouse gas emissions savings could equal 369 megatonnes, or around 1% of global emissions.
However, the carbon-reducing capacity of bio-based goods cannot be taken for granted. In this article, we look at how biofuels and biomaterials can best contribute towards global carbon reduction targets, as well as how they can undermine them.
What is the bioeconomy?
Although bio-engineering and advanced materials now dominate perceptions of the bioeconomy, it actually includes any economic activity that uses biological materials as feedstock or processing tools. Synbio and forestry both qualify.
These diverse sub-sectors all ultimately depend on well-functioning habitats, whether these are wild or managed. Developers of bio-engineered enzymes or biopharmaceuticals source industrially useful strains from genetically diverse wild stock. Bioplastics depend on agriculture and forestry for high volumes of cheap biomass.
The manufacturing and land-based parts of the bioeconomy are knitted together in intricate supply and demand relationships. Agriculture and forestry deliver feedstock to bio-manufacturers. Biotech companies develop new solutions for crop production and environmental management.
The relationships between these sub-sectors profoundly shapes how much the bioeconomy overall is reducing emissions. This is because the carbon footprint of bio-based goods all depends on how their feedstock is produced.
Why land use and habitats matter
When we think about the carbon reductions associated with biofuels, we think of transport. However, getting an accurate picture of the global net emissions impacts of biofuels requires taking account of its impact on land-based activities.
All biomanufacturing feedstock can be traced back to either agriculture, forestry, and other land use sectors (collectively known as AFOLU).
Between 2010 and 2019, agriculture, forestry, and other land use sectors contributed around 5 gigatonnes of net carbon emissions per year. However, the IPCC says it is among the most promising areas for emissions cuts, potentially contributing 20-30% of the total 2050 emissions reduction targets needed to limit global warming to 2 degrees.
Habitat management – decisions about how land is used – is the part of AFOLU that offers the biggest carbon savings. Part of why habitat management is so critical to global reduction efforts it provides feedstock for biofuels and biomaterials production, an essential part of easing our dependence on petrochemicals.
All carbon mitigation scenarios modelled by the IPCC carve out some role for biofuels. This is a proven technology with the capacity to reduce petroleum and natural gas use, especially in aviation and shipping where battery-stored renewable electricity is not an option.
Playing a supporting role in renewable fuels expansion is not the only way that habitat management can contribute to carbon reduction. It is also important for determining how much feedstock is available for making renewable materials.
Forestry, for example, may become an important base for more sustainable manufacturing. The IPCC mitigation report from last year states that the increased use of wood in buildings can reduce GHG emissions from cement and steel production’ while timber forests themselves provide carbon storage’. Already, bio-based composite materials are starting to replace traditionally mined components for wind turbines, electric battery anodes, and automobile parts.
There is a third way that habitat management decisions can help meet emissions reduction goals: by maximising carbon locked up in natural ecosystems. Across the world, wild, semi-wild, and cultivated habitats sequester an average of around 7.2 gigatonnes of carbon emissions a year.
Bio-manufacturing can decrease habitat carbon storage
Bio-manufacturing has an uneasy relationship with this conservation-based side of climate mitigation. Growing cheap, abundant feedstock for biofuels means either high-intensity cultivation, increasing how much land is put under cultivation, or both.
Farmland tends to store less carbon than the natural habitats they replace, potentially offsetting the carbon savings of switching from fossil to biofuels.
As the IPCC has written, “while increasing and diversified use of biomass can reduce the need for fossil fuels and other GHG-intensive products, unfavourable GHG balances may limit the [overall] mitigation value”.
The UN body concludes that ‘growth in biomass use may in the longer term … be constrained by the need to protect … essential ecosystem services’, like carbon sequestration.
Certain cultivation methods can increase soil carbon and reduce the final carbon footprint of crop-based biofuels. However, the ability of farmers to adopt climate-friendly methods is constrained by market forces.
Right now, bio-manufacturers do not have strong incentives to favour feedstock suppliers striking the best possible trade-off between crop productivity and carbon storage.
While mandates for biofuels are now commonplace, few reward sourcing or growing sustainable feedstocks.Measuring the carbon stored by crop soil to certify sustainable farms is also notoriously costly.
For these reasons, many campaigners advocate investing in biofuels made using organic waste – cheap, land-efficient feedstock that can result in fuels with neutral or even negative carbon footprints. However, this is a less technologically mature option than older, crop-based fuels. Despite lobbying pressure, the EU voted to reject outright bans on the latter in 2022.
Caution is needed over the way the biofuels industry is impacting overall net emissions figures for the bioeconomy as a whole. Between now and 2050, consideration must be given to how the industry is impacting carbon stored in the habitats they use for feedstock and the vehicle emissions reduced when consumers switch to biofuels.
Scaling biofuels serves global carbon reduction goals but only up to a point. The IPCC provides figures for how much bioenergy we should aim to produce once accounting for the constraints of both food security and biodiversity. By 2050, we could potentially make 5–50 extrajoules of bioenergy per year from the waste products of forestry and food agriculture and 50–250 extrajoules from crops devoted to making biofuels.
We still have a long way to go before meeting these volumes. In 2021, the International Energy Agency says the world produced around 15 extrajoules from modern bioenergy (products like biogas and biofuels, excluding traditional fuels like burning wood). But more is not always better from a mitigation perspective.
For biofuels to offer net carbon reductions long term, the location of new fuel crop sites must be carefully regulated. Scaling should be targeted at applications where battery power is not an option, meaning shipping and aviation rather than automobiles.
Bioplastics are not always greener
Similarly, biomaterials contribute best to mitigation when deployed strategically. Investment and scaling should be targeted at applications in areas where “full decoupling from carbon is difficult to achieve”, like plastics and chemicals.
According to the IPCC, bioplastics are particularly well suited to improving the carbon footprint of food packaging. Even here, however, the biomaterials sector needs to look carefully at whole-life, product-specific impacts. This is particularly important as most bioplastics feedstocks today are from food crops.
In 2021, a full life cycle assessment found that switching from petrochemical plastic to maize-based PLA bioplastic packaging for fresh fruit and vegetables could actually be more environmentally damaging than ordinary plastic when looking at the total impacts of feedstock, manufacturing, use, and end-of-life processes.
End-of-life recycling and disposal decisions make all the difference. The PLA was likely to have a worse environmental outcome than petrochemical plastics where there was no diversion of organic waste (of both packaging and the food contained within it) to biowaste treatment.
Feeding bioplastic waste to insects was the most environmentally beneficial recycling method, the study found. Insects can convert low-value organic matter into high value products extremely efficiently. In fact, this remains among the least scaled but most promising carbon-reducing technologies that can be developed by the bioeconomy.
As well as the choice of recycling method, it found that the energy efficiency and location of PLA manufacturing heavily influences the overall environmental footprint.
Overall, the study highlights how material substitution is not enough to achieve net negative carbon emissions – the nature of the feedstock is all-important. The carbon footprint of bioplastics is also influenced by a wider infrastructural context. For net emissions reductions to come from switching to bioplastics, there must be a viable system in place for sustainable end-of-life processing.
The importance of emissions from recycling in the final carbon footprint of a bioplastic signals how circular solutions are generally a good rule of thumb for industry to aim for. This requires cross-sectoral collaboration: bioplastics producers developing products in collaboration with bio-waste processing start-ups, and industry working in concert with public authorities to organise effective waste feedstock collection.
More life-cycle assessments needed
Right now, the biomanufacturing industry is overwhelmingly focused on scaling. More attention is needed to what exactly is being scaled.
In assessing the climate benefits of particular products, our focus often falls on scope 1 emissions. These are all emissions made at the point of consumption – for example, the emissions associated with burning biofuels rather than fossil fuels in a plane.
From a global emissions perspective, the carbon emissions of the whole product life cycle, from feedstock to recycling, are just as important as the emissions displaced when a consumer swaps fossil fuels for renewables. This is heavily context dependent: even within the same group of materials, like PLA or bioethanol, we could see dramatic variations in net carbon emissions depending on where the feedstock came from and the regulations of particular countries for waste processing.
The questions that the biofuels and biomaterials industries must ask are: How much carbon does a particular piece of feedstock cropland absorb compared to the habitat it replaced? Does a product displace petroleum consumption to the extent it still offers an overall net carbon emissions reduction despite replacing a carbon-rich habitat at the upstream end? Only by addressing these nuances of the carbon calculus can these industries claim to be advancing net zero goals.
