On a windy July day in 2017, temperatures started climbing early in Pauma Valley, California, an unincorporated community about 50 miles northeast of San Diego. Staff at Solidarity Farms, a 10-acre cooperative, were busy that morning, preparing for a 30-degree spike in temperature. 

They watched the chickens to make sure the flock had enough water and shade. Irrigation ran all day, dripping water into the sandy soil, though it evaporated just as quickly. As temperatures topped 120 degrees, Ellee Igoe, a co-owner at the farm, was shocked and overwhelmed as she tried to manage the heat, her young children, and no air conditioning. “We were trying to keep ourselves alive, let alone trying to keep everything else going,” she said. 

Nearly all the chickens died. Huddled under the coop, some hens seemed to have been overwhelmed by body heat from the birds that surrounded them. A few days later, Igoe could see the impact on the crops. Vine plants, like pumpkins and cucumbers, particularly suffered, she said, because they struggled to pump water through their spindly stems and out to their leaves. 

After that day, the farm changed course. Today, Solidarity Farms, which sits on a plot of land leased from the Pauma Band of Luiseño Indians, farms not only fruit and vegetables, but also carbon. Starting with funds received from the state of California in 2017, Solidarity Farms began incorporating practices that improve soil and help suck carbon out of the atmosphere, like spreading compost and reducing tilling on fields, rather than applying fertilizer or plowing. The farm applied for the money after the devastating heat. It was a shot, they hoped, at making the farm more resilient to the changing environment. Any potential carbon sequestration would be an added benefit.  

Now, California legislators are considering promoting those same types of practices on more farms, by establishing an overall greenhouse gas reduction target for the state’s “natural, working, and urban lands.” A bill under consideration  would create new natural carbon sequestration programs and boost greening the state’s cities and suburbs. Supporters of the legislation see the goal as an important step toward California meeting its climate targets while using its ample farmland. 

If passed, the bill would appear to be the first setting such a state target by law, said Torri Estrada, executive director at the Carbon Cycle Institute, an organization that advocates for nature-based carbon removal that co-sponsored the bill. Estrada says U.S. climate strategy has largely framed policy around emissions reductions, but the bill would create the same sort of high-level climate target for land use that’s already been established for sectors like transportation and electricity. That’s one reason why assemblymember Cristina Garcia introduced it. 

“We want to make it clear where we expect the Department to go, and give them clear direction,” Garcia said. The bill would need to pass before the legislative session ends in August and sponsors are hopeful about its chances. 

Regenerative agriculture practices boost soil health in part by increasing its carbon content. But  climate policies relying on carbon farming are also controversial. 

In 2019, the United Nations Intergovernmental Panel on Climate Change estimated that, worldwide, soil on croplands and grasslands could sequester anywhere from 0.4 to 8.6 gigatons of greenhouse gases per year. But in recent years a range of experts have questioned our ability to rely on natural carbon sequestration and regenerative agriculture practices as climate solutions. 

Experts at the World Resources Institute and scientists at universities like Purdue and Colorado State have raised concerns about how accurately that carbon can be measured and monitored over time and across varying geographies at scale. In 2021, environmental groups like Food & Water Watch and Friends of the Earth sent a letter to federal lawmakers asking them to vote against a climate bill creating a voluntary carbon market that would include farmers, instead urging them to support policies that build local food economies and make farming more sustainable. 

Still, other university scientists argued in a 2020 paper that “the science is clear” that regenerative agriculture can contribute to fighting climate change, and that all solutions must be used in confronting the challenge.

“There is quite a bit of consensus that there is no consensus on the effectiveness of practices, annual [agricultural] practices in particular, such as tillage, to sequester more carbon,” said Silvia Secchi, a professor in the department of geographical and sustainability sciences at the University of Iowa. 

California’s bill, which has already passed the state assembly, would set a goal of at least 60 million metric tons of carbon dioxide removed from the atmosphere each year by 2030 through natural carbon sequestration (in 2019, the state emitted 418 million metric tons of carbon dioxide equivalents). That would sequester enough carbon annually to equal yearly emissions from nearly 13 million gas-powered cars. California’s target would increase to 75 million metric tons per year by 2035. 

The bill as written requires the state Natural Resources Agency and the Department of Food and Agriculture to hash out how the state will actually achieve that removal. The sequestration goal would not become part of California’s existing cap-and-trade program and would add to the state’s commitments to slash greenhouse gas emissions, rather than count toward those targets. 

Carbon Cycle provides technical assistance to farmers across the state on how to incorporate longstanding practices like no-till agriculture and planting vegetation called cover crops, which can reduce erosion and add nutrients back to the soil, that now fall under the umbrella of carbon farming. Tillage, or plowing, land removes carbon from the soil and releases it into the air as carbon dioxide.

Solidarity Farms worked with the organization while it was implementing some of those techniques. Encouraging carbon sequestration on agricultural lands in California, which cover about 43 percent of the state, is a given, according to Estrada, because carbon sequestration is inherent to how plants grow. 

“Carbon sequestration is not just a technique; it’s part of photosynthesis,” Estrada said. “It’s what farming is.”

Others, though, are more skeptical. 

Aside from concerns about the climate potential  of natural carbon sequestration, the legislation’s greenhouse gas target is ambitious, higher than most existing scientific estimates for potential carbon removal for natural lands in California, according to Daniel Sanchez, a professor at University of California, Berkeley who runs the school’s Carbon Removal Lab. He worked on a 2020 Lawrence Livermore National Laboratory report that found that California’s natural lands could sequester 25 million tons of carbon dioxide per year and that the state needs to sequester 125 million tons per year to reach carbon neutrality by 2045. A Nature Conservancy report from the same year found that the state could sequester about 514 million metric tons of carbon dioxide by 2050, which equates to an average of roughly 20 million tons per year. 

Natural climate solutions can also be impermanent. A farmer may not till her land, increasing its carbon content, but if plowing on that land restarts, all that carbon can be released. Likewise, when a tree dies and decomposes, the carbon taken up as it grows returns to the atmosphere. Drought and wildfire in California put trees at risk of mortality. 

Sanchez believes that California should encourage natural carbon removal, but that the state must also pursue technological solutions for capturing carbon. He recently took a leave from Berkeley to join Carbon Direct, a firm that advises other companies on carbon-removal technologies and that invests in companies commercializing those technologies.

“We’re ultimately going to need engineered carbon-removal technologies,” he said. “The question is always ‘How much?’ and ‘How quickly?’ and ‘How much could we use these nature-based sinks as complements?’” 

Measuring how much carbon natural projects actually sequester is also notoriously tricky, although the controversy has largely centered on using natural sequestration as offsets that are then sold to polluters, which California’s new bill would not allow. Some experts like Sanchez  have also raised concerns with the expense and techniques used to rigorously account for carbon sequestered using natural methods. 

Igoe at Solidarity Farms hesitates to provide an estimate of how much carbon the farm has stored since it changed some of its practices, in part because she’s seen so many strategies for measuring it, such as modeling and on-farm sampling. And she sees it as an ancillary benefit, anyway. She’s more interested in the health of the soil, in which organic matter rose from 1 percent to 7 percent in their no-till vegetable beds. That increase helps the soil hold thousands more gallons of water. On hot days, the improved soil acts like a sponge. 

“It just holds onto water longer. That was the aha moment—‘OK, we’ve got to get off the tractors, we’ve got to think about really focusing on soil,’” she said. “The reason to do this kind of farming is definitely to sequester greenhouse gas emissions. But more importantly—and this goes back to the root of why we even started this in the first place—it’s to build on-farm resilience, so that our local food system has some resilience.”