Biofuels Are a Controversial Climate Solution. Could They Still Help Save the Planet?

by Emily Pontecorvo (Grist) Two recent studies add fresh evidence to both sides of an age-old debate. ... (Lee) Lynd’s study aimed to address the common claim that biofuels do not actually offer greenhouse gas benefits.

Ignoring factors like biodiversity and economics, Lynd and his coauthors calculated the potential avoided fossil fuel emissions from growing a crop called switchgrass in three different places — on abandoned agricultural land, pasture land, or land where a young forest has been cleared. The switchgrass would be turned into ethanol that would replace the gas in your car. For each location, they compared the results to the potential climate benefits of other land use choices, like reforestation, grassland restoration, or in the case of an existing forest, just letting it be.

As one might expect, chopping down a young forest to grow switchgrass did not produce optimal results. That would put the biofuel operation in immediate and immense carbon debt, and it would take too long for the avoided fossil fuel emissions associated with biofuels to make up for it. But the researchers found that on former cropland or pasture, so-called “marginal land,” with little agricultural value, growing switchgrass would have about the same greenhouse gas mitigation potential as restoring the land to forest, and potentially twice the benefits of restoring it to grassland.

In a third scenario, they calculated the added benefit of capturing the carbon dioxide that’s typically emitted during the process of converting the grass into fuel and storing it deep underground. With carbon capture and sequestration, switchgrass could mitigate about four times as much carbon pollution as trees can.

“What they are showing is that these advanced biofuel technologies can get much more carbon sequestration for that unit of land than replanting a native forest,” said (Daniel) Sanchez. “It challenges this idea that the best use for everything is to just reforest, reforest, reforest the world.”

But forests are considered a negative emissions technology too, as long as there’s some guarantee they’ll be preserved. That’s why (Tim) Searchinger was not won over by the study’s results for BECCS. “They are missing the notion of opportunity cost,” he said. What he means is the potential for a win-win situation — for the land to be reforested, and for the same amount of energy to be produced in some other way.

In the study, the authors note that sequestering carbon from biofuels deep underground could potentially be more permanent than planting trees, since climate change will make forests increasingly vulnerable to wildfire. They also point out that growing switchgrass is a potential revenue stream for landowners. And there are other considerations that are harder to predict, like how quickly different technologies can scale and be adopted. Airplanes and ships have long lives, so converting a fleet to run on new technology like hydrogen fuel won’t happen overnight. Plant-based fuels can be blended with traditional fuels and “dropped in” to existing engines today.

There are other ways to get negative emissions, including big “direct air capture” machines that pull CO2 straight out of the air. Another recent study asked whether large-scale deployment of these machines could alleviate some of the strains that an expanding biofuels industry and reforestation would put on food, land, and water availability. These facilities are currently expensive and energy intensive, but unlike BECCS, they can be placed pretty much anywhere, and they don’t require as much water.

The researchers modeled and compared ways to limit warming to 1.5 degrees C (2.7 degrees F), the goal of the Paris Agreement, with and without direct air capture. They looked at how much carbon we might need to remove if the world moves quickly to get to net-zero emissions in the next few decades, versus a more gradual reduction in emissions. For the scenario that included direct air capture, the model chose the most cost-effective mix between that, BECCS, and reforestation.

What they found was that direct air capture could soften the blow of biofuels, so to speak, when it comes to land use. But even with prompt action to get to net-zero emissions, the level of BECCS and reforestation needed to hold global warming to 1.5 degrees C by the end of the century could still cause food prices to double or triple around the world by 2050, and get even higher in the Global South. The model showed that water use would still go up dramatically as well, because so many direct air capture facilities would need to be built that it would cancel out the water benefits of growing fewer bioenergy crops. And the energy required to power these carbon-sucking machines would be monumental: It would be equivalent to more than all of the natural gas the world consumes today.

One caveat to these results is that the models assumed that if direct air capture were available at scale, it would reduce the need to green up industries like transportation, because the machines could be used to offset continued emissions.