Burning plants plays a significant role in the modern energy mix, but needs to meet strict sustainability standards to benefit the climate

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For as long as the human species has been around, we’ve burned plants to meet our needs. Millennia before humans were burning oil and gas, we were burning wood for heat and light.

Nowadays, plants are still used for heat and light, particularly in rural parts of the developing world. They’re also burned to spin turbines which provide electricity or power vehicles’ internal combustion engines. The various fuels derived from plants are collectively known as bioenergy.

They make up more of the modern energy mix than you might think, accounting for one tenth of global primary energy supply. While wind turbines and solar panels are the images that spring to mind when we hear “renewable”, bioenergy is also classified that way, attracting policy support. As of 2019, biomass was the biggest renewable energy source in the EU, at 60% of the total.

But the role for bioenergy in tackling climate change is fiercely disputed. “Renewable doesn’t necessarily mean sustainable,” said Stockholm Environment Institute’s biofuels expert Francis X Johnson.

That’s because the world has a limited amount of land. If it’s being used to produce energy crops, then it’s not being used to grow food or restore carbon-rich ecosystems. With food prices and hunger rising, and deforestation damaging the climate and taking away animals’ habitats, the question of how best to use land is increasingly sensitive.

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In its authoritative summary of climate science, the Intergovernmental Panel on Climate Change (IPCC) said in 2022 that “reconciling bioenergy demands with food and biodiversity, as well as competition for land and water, will require changes in food systems – agricultural intensification, open trade, less consumption of animal-products and reduced food losses and advanced biotechnologies”.

The source of the bioenergy matters. Waste feedstocks like used cooking oil or sawmill offcuts are generally uncontroversial, but they may not match the scale of demand. Specially grown crops vary hugely in their carbon impact, depending on the species, location and management plan.

Limited supplies of sustainable bioenergy should be prioritised for hard-to-decarbonise sectors, experts told Climate Home News. For things that can be electrified like cars, solar and wind power are usually a better solution. Air travel, long-distance shipping and heavy industry, on the other hand, are still expected to need combustible fuels.

What is the climate impact of bioenergy?

Whether biofuels are better or worse than fossil fuels depends on how they are grown.

Sweden, which has a small population relative to its forests and a legal duty to replace every felled tree, offers a positive case study.

Over the last 50 years or so, Sweden’s use of biomass (mainly wood) for district heating has soared, massively reducing emissions intensity compared to oil-fired boilers, while the area of forest cover has increased.

In other cases, energy crops displace forest or other ecosystems that would otherwise be valuable carbon sinks, which is bad for the climate.

Energy crops like sunflower, wheat or rapeseed, planted annually, Johnson said, “normally have a less favourable carbon balance” than trees. Perennial grasses like sugarcane and miscanthus (silvergrass) can have a better carbon balance “under the right conditions and uses. And it depends on the management, the use, and the suitability of soils and climate for different trees and crops”.

A eucalyptus forest in Kenya (Photo: Flickr/CIFOR)

According to the European Sciences Advisory Council and the Joint Research Centre, the only types of woody biomass which are good for the climate and not bad for nature are twigs and small branches from coniferous forests and wood grown with low intensity on former farmland. Even then, some of the twigs should be left behind for soil fertility, they say.

The most sustainable type of biofuels are those which would otherwise be burned as a waste product or go into landfill. These include agricultural waste, used cooking oil and uneaten food.

The Indonesian government plans to use oil palm plants to partly replace coal in power stations. The plants will be burned once they’ve grown too old to produce oil.

Fabby Tumiwa, an adviser to the Indonesian government and director of the Institute for Essential Services Reform think tank, told Climate Home: “In the past, they just burned it. So the idea now it to use that as a biomass feedstock… I am sure we will not cut any forest.”

This would only be economic when the oil palms are within 50-100 km of the power station. “Beyond that, I think it’s too expensive,” he said.

Scalability is another consideration. Fast food chain McDonald’s its ready supply of used cooking oil to power delivery trucks. But, Transport and Environment researcher Laura Buffet said: “The quantities are quite limited. It’s not like you can power the entire transport sector with waste oils. Otherwise, we’ll end up just eating fries every day to make sure we can run transport on [the used cooking oil].”

And the premium put on used cooking oil raises the potential for fraud. The UK and Netherlands have launched investigations into suspected misselling of imported virgin oils as waste.

Comment: Nature restoration and carbon removal are not the same. Here’s why it matters

As well as the climate impacts, where biofuel crops displace food crops, it pushes up food prices. The IPCC says growing biofuels for transport could conflict with the UN’s sustainable development goals on eradicating hunger.

It recommends targeted support for food security, more efficient agricultural methods and less meat-eating as ways to reduce this conflict.

Global food prices have spiked since Russia invaded Ukraine in February, disrupting supplies from two major producers of grain and sunflower oil. This has led to renewed calls to use these crops for food not fuel.

The use of biomass – usually wood pellets – for electricity generation globally has increased steadily over the last twenty years and the International Energy Agency forecasts it will double by 2030 in its net zero by 2050 scenario.

The use of biofuels for electricity has grown steadily. (Photo: International Energy Agency)

Its growth has been supported by government policy. For example, in 2009 the European Union classified biomass as carbon neutral. “It wasn’t foreseen that it would be big so it wasn’t investigated very thoroughly,” said Ember analyst Tomos Harrison.

Following this classification, EU countries subsidised power stations which switched, partially or fully, to using biomass instead of coal.

But burning wood causes emissions at the power plant and in the supply chain, which are not fully offset by the trees absorbing carbon when they grow. Scientists have become increasingly assertive at pointing this out. The European Academies Science Advisory Council (EASAC) says that using wood for electric power “is not effective in mitigating climate change and may even increase emissions”.

EASAC scientist Michael Norton said: “Labelling forest biomass as renewable has a perverse impact on the climate. Much of the biomass employed in Europe is anything but carbon neutral.”

The UK government’s official and independent advisers on the Climate Change Committee found in 2018 that “biomass can play an important role in meeting the UK’s long-term emissions targets… but only with stricter governance to ensure sustainable supplies”.

The EU tightened the criteria for sustainable biomass in 2018, and campaigners and industry continue to wrangle over where the line should be drawn in a revised renewable energy directive.

Transport – save it for the heavy stuff

In the race to decarbonise cars, motorbikes and buses, electrification is winning. Electric motors are significantly more efficient and lower maintenance than internal combustion engines, whatever the latter is fueled with.

In the short term, though, electric charging infrastructure is patchy. Biofuels, in the form of ethanol, have the advantage that they can be blended with fossil fuels and used in filling stations.

This argument has won policy backing in many places, notably US and Brazil, at significant cost to governments and consumers.

Despite mounting evidence bioethanol might do more harm than good to the climate, it’s mandated for political reasons. Farmers in the US swing state of Iowa want to keep putting their corn into cars and no presidential candidate can afford to deny them that. The Brazilian sugar industry is similarly powerful.

An E85 (85% ethanol) gas pump at a fueling station in Minnesota. (Photo Wikicommons)

Other forms of transport, which have to carry heavier loads or travel longer distances between charging points, are much more difficult to electrify.

The IPCC scientists say that “electrification tends to play the key role in land-based transport, but biofuels and hydrogen (and derivatives) could play a role in decarbonisation of freight in some contexts”.

“Biofuels and hydrogen (and derivatives) are expected to be more prominent in shipping and aviation,” the IPCC continues.

That’s because there’s unlikely to ever be a battery both powerful enough to propel a plane across the Atlantic and small enough to fit on such a plane.

Similarly, a container ship travelling between Shanghai and Los Angeles can’t re-charge its battery in the middle of the Pacific Ocean.

This is where biofuels could make sense. Given the concerns around land use, there have been experimental efforts to make jet fuel from algae, although they are long way from commercial viability.

Whatever biofuels are used for, how they are produced matters, Johnson said. “Biofuels can cut emissions as well as contributing to sustainable development. But life cycle assessment and context-specific analysis is needed to determine the existence and significance of these benefits.”

This article is the second in a four-part series on the future of energy. Hero image: Biomass at Tofte, Norway (Statkraft/Flickr).

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