Uncertainty prevalent in soil carbon markets

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While initial focus is on carbon sequestration, other opportunities also exist with immediate climate benefits.

Scientists estimate that agricultural soils could remove 4-6% of annual United States emissions, but the current system lacks verification to know if soil carbon credits are encouraging actions to close in on those targets. Credits for soil carbon sequestration currently lack comparability and consistency, which creates uncertainty in soil carbon markets. Efforts are underway, however, to improve the quality of credits and help realize the full greenhouse gas mitigation potential of agricultural soils. 

In a new report — Agricultural Soil Carbon Credits: Making sense of protocols for carbon sequestration and net greenhouse gas removals — Environmental Defense Fund and the Woodwell Climate Research Center reviewed the 12 published protocols used to generate soil carbon credits through carbon sequestration in croplands. The protocols take different approaches to measuring, reporting and verifying net climate impacts, and to managing the vital issues of additionality, reversal and permanence. The result is a confusing credit marketplace where it is difficult to compare credits or guarantee climate benefits have been achieved, the organizations note.

“As addressing climate change becomes ever more urgent, we’re seeing a gold rush of investment in soil carbon credits. The stakes for the climate and farmers are extraordinarily high,” says Emily Oldfield, lead report author and agricultural soil carbon scientist at EDF. “Agricultural soils could remove 4-6% of annual U.S. emissions. We need credible, consistent and cost-effective measurement and verification to know with confidence that soil carbon credits are moving us toward that target.”

Public and private sector efforts are underway to improve measurement technologies and methods and to set unified standards for high-quality agricultural carbon credits that accurately represent carbon sequestration and net greenhouse gas removals.

Soil carbon protocols take different approaches to measuring, reporting and verifying net climate impacts, and to managing the vital issues of additionality, reversal and permanence. This variation makes it difficult to ensure climate benefits have been achieved.

“Until these variations can be resolved, paying farmers to sequester soil carbon will remain an uncertain approach to greenhouse gas mitigation but can still deliver important benefits for climate resilience, soil health and water quality,” the report notes.

The Senate overwhelmingly passed the Growing Climate Solutions Act earlier this summer to direct the USDA to set guidelines for high-quality agricultural carbon credits. The House has introduced its own version but has not taken up the bill itself. Callie Eideberg, director of agricultural policy for EDF, says, “USDA must be ready to swiftly implement the bill when it becomes law to increase certainty that markets deliver for farmers and the environment.”

Related: Landmark Growing Climate Solutions Act clears Senate

Agricultural soils can contribute meaningfully to climate mitigation and resilience efforts. Once guidelines and standardization between protocols are in place, the enthusiasm for soil carbon credits can be channeled productively toward slowing the rate of climate change and adapting to impacts that are already here. This will benefit both farmers and the planet, EDF adds.

“Businesses face intense pressure to reduce emissions at the pace and scale that the science demands,” says Katie Anderson, senior manager for EDF+Business. "Companies must focus on reducing emissions from their own operations and supply chains, as well as investing in high-quality carbon credits. But, it’s crucial that both soil and forest carbon credits have environmental integrity, guidelines for use and that they’re integrated into a clear pathway to decarbonization.”

Soil carbon remains difficult to measure for a variety of reasons. While scientists understand how soil carbon responds to farm management changes, scientists can’t currently predict the amount and longevity of new carbon sequestration on all farms. Detecting soil carbon changes over time requires a high number of samples, which are costly to collect and analyze, and may need to be collected from different soil depths depending on soil type and conservation practices used.

“There are exciting new research efforts and technological developments underway that will greatly reduce the cost of verifying soil carbon credits,” says Jonathan Sanderman, contributing report author and associate scientist at the Woodwell Climate Research Center. “Increasing accuracy at scale, while also being able to pass on most of the value of a carbon credit to the farmer, is critical to ensuring functioning carbon markets.”

Researchers can advance technology that will make it easier to measure soil carbon levels over time and more cost-effective to verify carbon credits.

Beyond just soils

While much of the current attention is focused on soil organic carbon sequestration, the opportunities to reduce emissions associated with agricultural activities are equally worthy of consideration, as their mitigation potential is large, and they have many advantages over soil organic carbon sequestration as a mitigation strategy, the report notes.

For instance, reduction of fuel consumption, methane emissions or fertilizer inputs results in avoided emissions that are permanent and therefore do not have the risk of reversal. Without the risk of reversal, there is no need for risk management requirements like maintaining a GHG offset credit buffer. Avoided emissions are also immediate, unlike soil organic carbon sequestration, which takes many years to accumulate to measurable levels.

An important avoided emissions opportunity for farmers is the reduction of nitrous oxide emissions from soil. Nitrous oxide is a potent GHG with a global warming potential of 265 over 100 years or 264 over 20 years, the report explains.

Agricultural soils are responsible for 78% of nitrous oxide emissions in the U.S., representing about 5% of total GHG emissions on a 100-year time frame. “By optimizing manure and inorganic fertilizer application, many farmers can save money and reduce nitrous oxide losses from soils, while also reducing nitrate leaching and providing water quality benefits,” the report adds.

Capturing biogas, which is usually more than half methane, currently emitted from manure management systems can provide permanent, immediate climate benefits, as well as revenue since biogas can be processed to pipeline-grade methane.

Livestock also produce methane via enteric emissions. The report states, “Work is underway to develop feed additives or diet changes to reduce enteric emissions, and protocols to credit those avoided methane emissions are being considered. However, getting such feed additives to grazing beef cattle, where most livestock methane emissions occur, will be a challenge.”

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