Regulators need to take a closer look at the impacts of biofuel production on land use and the carbon intensity of anaerobic digesters as they develop lifecycle assessments for transportation fuels, a National Academy of Sciences report says.

Despite “intense study over the last decade” on whether, or to what extent, biofuel production replaces food production and affects the environment, “substantial uncertainties remain on many key components of economic models used to assess these impacts,” the report said, calling for more work to be done.

The report, which did not evaluate specific transportation fuel options, comes as the Environmental Protection Agency considers making Sustainable Aviation Fuel (SAF) and electricity from biogas eligible for pathways under the Renewable Fuel Standard.

“New fuels like SAF, as well as other new pathways for RFS compliance, such as electricity generated from biogas that may be proposed for so-called ‘e-RINs,’ must be accommodated in a fashion that is additive to existing fuel technologies and previous blending targets,” 13 senators wrote to EPA Administrator Michael Regan in a letter Wednesday. “They must also be subject to the same rigorous transparency, integrity, and lifecycle analysis standards as other renewable transportation fuels.”

In an email to Agri-Pulse, Geoff Cooper, president and CEO of the Renewable Fuels Association, called the NAS effort “largely an academic exercise” and disputed some of its conclusions.

“We don’t expect it will have much impact on current or future low carbon fuel policies and regulations, including the RFS ‘set’ rule that EPA is currently working on,” he said referring to the multiyear blending targets EPA is expected to propose next month.

Cooper also said the report “seems to exaggerate the level of uncertainty associated with lifecycle analysis of biofuels. By now, the direct carbon impacts of producing biofuels are fairly well known and understood. And empirical data and hindsight have shown us that the speculative and ‘uncertain’ land use changes that were predicted more than a decade ago simply have not occurred.”

More data and study are needed, he said, but “more current and more robust data sets would surely show that the carbon intensity of biofuels like ethanol is even lower than current models suggest,” Cooper said.

The NAS report said changes in the regulation of confined animal feeding operations such as dairies could increase the carbon intensity (CI) scores now assigned to the production of biomethane in California under its Low Carbon Fuel Standard.

“The most significant fuels with large negative CI scores under existing policy are based on biomethane from manure,” the report said. But those large negative scores “arise from the assumption that confined animal feeding operations will store manure in lagoons, thus emitting methane to the atmosphere, and LCFS support for the use of manure-derived biomethane will result in the construction of enclosed anaerobic digesters that would otherwise not have been constructed.”

However, the scores would go up if policies were enacted requiring all such feeding operations to manage their manure in enclosed anaerobic digesters, the report said.

“Similarly, by capturing the reduction in emissions for the LCFS, no reduction in emissions can be assigned to the animal food product pathways,” the report said. “Policy or practice changes that reduce assumed manure methane emissions outside their use for transportation fuel would require an update to the life cycle, which could reduce or eliminate the negative emissions presently associated with the fuel pathway.”

Tyler Lobdell, an attorney with Food & Water Watch, which has petitioned California’s Air Resources Board to exclude from the LCFS fuels derived from biomethane from dairy and swine manure, agreed with the report.

“It’s the failure to regulate air emissions from CAFOs that has led to the extreme negative carbon intensities,” he said. Dairy operations in California, he said, are “rewarded” by using manure flushing and lagoons that they knew would result in air pollution and GHG emissions, which allows them to be paid for “’capturing’ methane they are intentionally generating, and in the process further encouraging concentration of herds and skewing market dynamics even more in favor of the largest, industrial-scale operators to the detriment of more sustainable, smaller-scale farmers.”

In an interview earlier this year, Mark Stoermann, chief operating officer of Newtrient, said emissions from dairy production and processing “have already been captured in the lifecycle analysis of dairy products.” 

He said that taking that into account, the LCA for biomethane only looks at manure management, resulting in negative carbon intensity scores that fetch higher LCFS credit prices.

Newtrient is a dairy industry-funded research group founded by 12 cooperatives.

The report also said policymakers need to “exercise caution in crediting biorefineries for GHG emissions sequestration as a result of exporting co-products such as biochar, digestate, and compost, as it risks over-crediting producers for downstream behavior that is not necessarily occurring.” The NAS committee recommended that “credits generated from these activities must be contingent on verification that these activities are being practiced.”

It added, “Applying credits for carbon sequestration to soil or reduced use of fertilizer should require robust measurement and verification to prove the co-products are applied in a manner that yields net climate benefits.”

“Nutrient-rich materials such as compost only offer fertilizer offset benefits if they are applied in a manner that results in lowered net GHG emissions,” the report said.

“Research articles vary in their assumptions about the potential for carbon sequestration using biorefinery co-products as soil amendments, but many assume 80-85 percent of biochar is stable for at least 100 years whereas digestate and compost are not assumed to result in accumulation of stable carbon in soils,” the report said.

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Research designed to develop accurate estimates of changes in soil organic carbon is needed, the report said.

“Given the importance of soil organic carbon changes in influencing life-cycle GHG emissions of biofuels, investments are needed to enhance data availability and modeling capability to estimate soil organic carbon,” the report said. “Capabilities to evaluate permanence of soil organic carbon changes should also be developed.”

Research is also needed, the report concluded, on the use of sensors or remote methods to measure soil carbon.

The committee agreed “there is an important distinction between using LCA for policy implementation, policy design, and [Regulatory Impact Analysis.] In all cases, a rigorous accounting of process-level emissions (e.g., fossil fuel combustion emissions at a refinery, (nitrous oxide) emissions on farms, and (methane) leakage at compressed natural gas production facilities) is essential.”

On aviation fuels, the report called for more research on the climate impacts of soot, water vapor, sulfates, and nitrogen oxides by aircraft. In addition, “additional research is needed to determine how alternative fuels and airframe combinations ― particularly electric battery technology and hydrogen ― may impact aircraft efficiency and overall emissions.”

In a news release, NAS said “there is no single LCA method capable of answering all questions related to the climate impacts of a transportation fuel.” However, it found that both attributional LCA (ALCA) and consequential LCA (CLCA) “have important roles to play.”

ALCA “assigns portions of observed environmental impacts from human activities to specific goods and services” and can be used “to attribute emissions in well-defined supply chains and help identify opportunities to reduce carbon intensity throughout that supply chain,” NAS said.

On the other hand, CLCA, which NAS said “considers the consequences of a policy or decision, such as the market effects of production changes,” would be better used to understand the wide-ranging impacts proposed changes might have on net GHG emissions.

The report was requested by Breakthrough Energy, a Bill Gates-founded venture.

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