Initially hailed as a solution to soaring roadside carbon dioxide emissions – which rose by 26% between 1990 and 2008 – headlines have recently turned to the damage that feedstock-based fuel crops such as biodiesel might have on the planet’s climate.
This is because of indirect land use change (ILUC) that happens when arable land taken to grow fuel crops is then compensated for by clearing forests, wetlands and other natural habitats elsewhere in the world to grow the missing food.
Futuristic biofuels made from the residues of agricultural products or algae do not compete with food production and have a “crucial role” to play in mitigating carbon dioxide emissions, a new report says.
But even so, it cautions that care and more EU funding are needed to ensure that exploiting them does not have unintended consequences.
“Ambitious EU action on advanced biofuels would also help relieve concerns over ILUC effects of biofuels that increase greenhouse gas emissions and compete for productive land resources or with food production,” said Jason Anderson, a World Wildlife Fund (WWF) spokesman.
The WWF-commissioned report, ‘Smart Use of Residues’, proposes an investigation of the effects that removing residues can have on biodiversity, organic soil matter, greenhouse gas emissions and evaporation and soil risks.
The study was carried out by the German Biomass Research Centre and Öko Institute, with funding from the bioenergy company, Novozymes.
Crop residues are the leaves, seeds, straw, stalks and ‘stubble’ left over after a harvest, and turning them into an energy source has become a holy grail for advocates of green biofuels.
They do not require additional land use, and a study by Bloomberg New Energy Finance earlier this year estimated that 17.5% of currently available residues could be used as a feedstock for advanced biofuels.
“With this amount, enough advanced biofuels could be produced to replace over 50% of the forecasted 2030 gasoline demand,” said Steen Riisgaard, chief executive of Novozymes.
In May, the Danish company inaugurated a € 161 million enzyme plant - the largest yet – dedicated solely to advanced biofuels.
WWF envisages around a quarter of the planet’s total primary energy coming from agricultural residues by 2050, but still the report sounds a cautionary note.
Because ecosystems involve a fragile and intricate weave of interdependent factors, any changes can have an unanticipated ‘carbon debt’, or overuse of the carbon storage capacity of the Earth’s soil, vegetation and oceans.
“Carbon debt is the sequel to ILUC in the making,” one EU official told EurActiv. “We are risking a repeat of the same story with bioenergy but it will be bigger and nastier.”
Advanced biofuels could make a negative contribution to the carbon debt in several ways.
Animals and insects use agricultural habitats for shelter, fodder, mating and nesting, and underground fauna depend on organic matter. As crop production often depends on fauna, residue removal can threaten yields – and have implications on land use.
Organic soil matter – or ‘humus’ – works as a carbon sink by indefinitely storing chemical compounds and improving soil structure. The removal of crop residues can lead to its decline over time, affecting soil fertility and carbon sequestration.
Reduced soil coverage can also remove barriers to evaporation and the sun, causing changes in soil humidity and reduced crop protection from the elements.
Lars Christian Hansen, president for Region Europe at Novozymes, welcomed the report’s demonstration that advanced biofuels represented “an opportunity for Europe to lead in the decarbonisation of the transport sector globally while creating green growth and jobs in Europe.”
“But we need to do it right from the beginning,” he went on. “Policymakers need to take over and support advanced biofuels while guaranteeing their sustainability.”
Soil carbon is the largest terrestrial pool of carbon, and removing crop residues might lead to greenhouse gas emissions, as well as the increased use of CO2-emitting fertilisers and diesel, when straw is removed.