The study confirms the contribution of bioenergy to climate change mitigation

That biofuels can contribute to a cleaner global energy mix is ​​widely accepted, but the net benefits of bioenergy in terms of greenhouse gas (GHG) mitigation are questionable. Some argue, for example, that biofuels are not sustainable because converting non-agricultural land to grow energy crops could lead to a significant initial decrease in carbon storage, creating what is known as “biofuel carbon debt.”

A study by a cross-border group of researchers published in Proceedings of the National Academy of Sciences (PNAS) could help refute this argument.

The study showed that the GHG mitigation potential of panic rod cultivation for cellulosic ethanol production in the United States was comparable on a per-hectare basis to that of reforestation and many times greater than that of lawn restoration. Panic rod (Panicum virgatum) is a widely cultivated native North American herb proposed as biomass for the biobased economy.

More advanced technology and the integration of carbon capture and storage (CCS) could further increase the mitigation potential per hectare of bioenergy systems by a factor of six, according to the study, which was supported by the São Paulo Research Foundation – FAPESP. through a guided project by John J. Sheehan.

Sheehan is affiliated with the University of Minnesota in the United States and is currently a visiting fellow at the University of Campinas’s School of Agricultural Engineering (FEAGRI-UNICAMP) in the state of Sao Paulo, Brazil, under the auspices of the (São Paulo Excellence Chair ( SPEC).

Study co-lead author Lee R. Lynd, professor at Dartmouth College in Hanover, New Hampshire (USA), initiated a project in February at UNICAMP’s Center for Molecular Biology and Genetic Engineering (CBMEG), with the funding from FAPESP under the SPEC program.

“The study details the factors and strategies that are important for implementing biofuel production in a way that helps stabilize the climate,” Lynd said.

Answers to questions

According to the authors, critics of bioenergy question whether raw material crops can be sustainably obtained without causing self-destructive reductions in carbon storage in the ecosystem.

In addition to the “carbon debt” resulting from the conversion of non-agricultural land into energy crop plantations, the use of existing productive agricultural land with low carbon stocks can also be counterproductive if food production is shifted and greenhouse gas emissions increase. somewhere else.

This effect, known as indirect land use change, can be minimized or avoided by growing raw materials for biofuels on low-yielding or abandoned farmland, or spared from continued agricultural use through future agricultural intensification or changes. in the diet.

Afforestation offers an alternative use of such land for greenhouse gas mitigation. However, it is often argued that the assessment of bioenergy production in these areas should consider their “opportunity cost”, which is the lack of carbon sequestration when land is used for raw material production rather than reforestation.

“The main studies published to date suggest a net change in land use of zero, but indirect land use change continues to be invoked as a key critique of biofuels,” Lynd said.

These arguments were initially directed at first generation biofuels, made from sugar, starch or vegetable oil in food crops grown on farmland, but issues have since been raised focusing on carbon debt, indirect land use change and cost. opportunities regarding the production of cellulosic biomass for use in advanced biofuel production or in electricity generation.

Based on these and other arguments, recent studies suggest that using land to produce bioenergy raw materials has a less than ideal impact in terms of climate crisis mitigation, and recommend that research and policy be reoriented towards management. Earth’s carbon biological.

However, these studies are often based on secondary estimates of the bioenergy system performance and the costs of mitigation opportunities. Additionally, they generally rule out consideration of CCS or future technology improvements, the authors note.

“Each of the criticisms we speak of in the study has some legitimacy in terms of indicating factors that can negate the beneficial impact of biofuels on the climate, but should not be taken as evidence that biofuels cannot or cannot have a beneficial impact.” Lynd said.

To refute the arguments presented by critics of biofuel sustainability, the researchers used ecosystem simulation combined with cellulosic and CCS biofuel production models, estimating the potential of energy grass biofuel to replace fossil fuels and sequester carbon directly. compared to other land-based mitigation schemes, such as reforestation and meadow restoration.

They calibrated the ecosystem model to perform temporally explicit simulations of atmosphere-biosphere carbon exchange with different land use choices at three case study sites in the United States.

The analysis showed that where farmers switched from rod panic to cellulosic ethanol, the mitigation potential per hectare was comparable to that of reforestation and many times greater than that of pasture restoration.

It also showed that the mitigation potential of plausible future improvements in energy crop yields and biorefining technology, along with CCS, could be four times that of reforestation and 15 times that of lawn restoration.

“Additionally, we found that natural land cover and supply chain technological maturity make a significant difference when it comes to estimating the relative benefits of greenhouse gas mitigation by biofuels and restoring natural vegetation,” he said. Lynd.

Growing panic rod can be especially beneficial in parts of the United States where natural plant cover is made up of grass rather than trees, according to the study.

In the future, the researchers plan to use the same modeling approach to discuss these issues for the United States on a national scale. “An important direction in which the study is pointing is the analysis of a wider range of sites, energy crops and conversion processes, including those designed to include biofuel production in a manner consistent with the circular economy,” said Lynd. .

The methodology could also be used to analyze the production of biofuels from sugar cane in Brazil, he added.