Where does bioenergy fit into a low-carbon future?

Biofuels like ethanol and other forms of bioenergy are often seen as a key part of a low-carbon future. But large-scale production of these fuels, which are usually made from either food crops like corn and sugar cane, or from woody plants and grasses, would represent a major shift in how the world makes its energy and uses its land — with implications for global food prices and natural resources like forests.

In a report released Thursday, researchers investigated what a large-scale increase in bioenergy production caused by a global carbon price might look like. The report concludes that changes spurred by the carbon price, including bioenergy production, could cut greenhouse-gas emissions by more than half, with a catch: To achieve the cut, the carbon price must cover emissions from changing land use. Without this safeguard, deforestation becomes a major concern as forests are cleared to make way for farmland.

If emissions from deforestation are included in a carbon price, bioenergy — together with other advances in clean technology — can reduce emissions 57 percent by 2050, relative to when there is not a carbon price. In comparison, not counting emissions from changing land use in the carbon price leads to a reduction of only 16 percent.

The study is one of the most in-depth evaluations to date of how bioenergy might fit into a low-carbon future. The research team developed a cutting-edge modeling tool covering a comprehensive range of bioenergy pathways. Researchers then used the new tool to consider interactions among bioenergy, other low-carbon technologies, and the economy in a world where bioenergy fuels about a quarter of global energy needs by 2050.

“Biofuels are only one channel for bioenergy,” says Niven Winchester, an environmental energy economist at the MIT Joint Program on the Science and Policy of Global Change. “If you want to study how land can be used to meet our energy needs, you have to think of all the different ways to use what grows on that land — including food, feed, and fuel.” 

Currently, ethanol made from corn and sugar supplies the majority of biofuel. But with new technologies, ethanol can be made from other materials; and there are other ways to generate energy from biomass. For example, the woody residues from logging and lumber processing can be turned into biofuels, or burned to produce electricity or heat for industrial processes.

If the technology to create and use it improves, researchers found that lignocellulosic ethanol becomes the dominant type of bioenergy by 2050. Lignocellulosic ethanol, a so-called second-generation biofuel, can be made from tough grasses such as switchgrass and Miscanthus. In some of their simulations, researchers assumed that the cost to produce lignocellulosic fuels would fall by about half over the next decade, as predicted by some analysts. They also assumed that technological improvements would eliminate the barrier to using a fuel mix with a high proportion of ethanol to gasoline, known as the “blend wall.” 

Under these conditions, lignocellulosic ethanol provides more than half of all bioenergy by midcentury. First-generation fuels mostly disappear from the market, but there continues to be a role for Brazilian sugar cane through 2050. If lignocellulosic fuels do become the norm, Africa and Brazil become the largest producers of bioenergy.

“Africa can become a key player in supplying global energy, if agricultural expertise can be transferred to this region.” Winchester says. “It has the right climate and a large amount of land, but also the potential for deforestation if policy safeguards aren’t in place.” 

Winchester cautions that, while biofuels could be a boon for areas with the right climate conditions, deforestation is a real concern. The researchers found that deforestation was likely to occur in areas with the weakest political constraints to clearing forests, regardless of where biofuels are actually grown. Deforestation was lessened, and in some cases reversed, when emissions from land-use change were included in the carbon price.

A policy like a global carbon price can lead to changes in land use when it increases the price of fossil fuels, making bioenergy more cost-competitive. This leads to changes in how land is used. Instead of growing soybeans, a farmer might decide to grow biofuel feedstock, or cut down a forested area to convert the land into farmland. Clearing forests increases emissions because trees are natural carbon reservoirs.

Because of its land requirements, bioenergy can put stress on other parts of the economy, especially food prices. Researchers found that large-scale bioenergy production would increase food prices by between 1.3 percent and 2.6 percent by 2050.

“Although many studies already exist on the potential of biomass for energy, they are often criticized because they fail to capture linkages between environmental and economic systems, which limits their value in informing sound decision-making,” says John Pierce, Chief Bioscientist at BP, which supported the work. 

“The work at MIT is advancing the state-of-the-art of bioenergy modeling,” Pierce says of the report. “It applies technical rigor to the assessment of the commercial potential of bioenergy, using a framework whereby economics is linked to land, climate, and ecosystems models. This provides an important and needed perspective in the overall discussion of the use of bioenergy in our energy future.”