By Katherine Ellison for Hothouse.
Broadcast version by Suzanne Potter for California News Service reporting for the Solutions Journalism Network-Public News Service Collaboration

Twitchell Island, Sacramento County, California - Steve Deverel gazes out over a levee on the San Joaquin River to a buoy where half a dozen sea lions are barking. It's a loud reminder that even here, 50 miles inland, some of California's most productive farmland lies perilously close to the Pacific Ocean. At any moment, a weak spot in the more than 1,000 miles of earthen levees protecting islands in the Sacramento-San Joaquin River Delta could unleash a salty deluge, threatening not just crops, but the drinking water for as many as 27 million Californians.

Deverel, a Davis-based hydrologist, refers to this threat as "The Big Gulp," a breach that would suck in tens of billions of gallons of river water, drawing ocean water in its wake. All it would take is some heavy rain, a moderate earthquake, or even hard-working gophers tunneling through earthen barriers first built in the late 1800s.

It wouldn't be the first time such a disaster happened.

On a sunny day in June 1972, a levee failed without warning or apparent cause near Andrus Island, about an hour's drive from San Francisco. Water ran four feet deep over the farmland. Thirty-foot cruisers and houseboats smashedagainst the embankments. Hundreds of homeowners fled rising waters, with several people seriously injured. In 2004-on another calm, sunny day-it happened again. This time the water turned 12,000 acres of prime California farmland into a brackish lake, costing $100 million in damages.

Deverel now hopes to save the Delta by flooding it before the Pacific can. And he wants to pay for it with carbon credits.

"Carbon-farming" in the wetlands

Deverel, 70, has spent three decades trying to head off the Big Gulp. Climate change is his chance. His project, funded to date by California state agencies and the University of California, has so far inundated 1,700 acres of Delta farmland on Twitchell and nearby Sherman island, transforming them into marshes of cattails and tule reeds. Each year, new plants growing in these restored wetlands will suck carbon dioxide (CO₂)-the most abundant greenhouse gas-out of the atmosphere, storing it in strata of accumulating muck that will help buttress the dikes in danger of collapsing.

The project passed its first important milestone on October 27, 2020, when the American Carbon Registry issued credits for 52,000 tons of CO₂ removed by the experiment, which is still in its very early stage. That makes this the first wetland project (and only one so far) to generate verified carbon credits in the US, according to Steve Crooks, a Sausalito, California-based wetlands scientist and global expert in the field of "carbon-farming" from coastal wetlands.

The Delta project is also one of very few such efforts around the world, yet its promise is enormous.

Even as they cover just 9% of the Earth's surface, wetlands are the largest natural carbon sink on land, sequestering an estimated 35% of the world's carbon stored on land, more than all other biomes combined. Since a majority of wetlands are degraded or destroyed, environmental scientists see restoring them as a huge potential source of carbon credits as countries and corporations ramp up their commitments to cut greenhouse gas emissions. Rehabilitating the earth's wetlands would provide myriad benefits in addition to carbon sequestration, possibly even more environmentally useful than carbon projects in forestry.

Yet managing these landscapes is a lot more complicated-and expensive-than simply flooding fields or replanting trees. Deverel believes the Delta project has revealed a path forward. The key is a rich, brown crumbly soil known as peat.

The promise of peat

A few thousand years after the end of the last Ice Age, the Delta was covered by a marshy, freshwater inland sea. Over millennia, layers of moss, mud, and vegetation accumulated to form peat. Under the right conditions, peatlands can store vast amounts of carbon. Marshes "sequester" or store CO₂ through photosynthesis as they grow, and the carbon stays trapped in the plants as they die and decompose underwater. Once drained, however, peat can be fabulous for growing crops, as farmers who came here after the Gold Rush soon discovered. The farmers, known as "swamplanders," hired Chinese laborers to build the levees and drain the marshes, and planted rows and rows of corn and alfalfa, much later adding other crops, including wine grapes, walnut and almond trees, cotton, sugar beets, and blueberries.

More than a century would pass before scientists realized the farmers were harvesting their own ruin.

The problem is known as "subsidence," a gentle word for a sinister situation. When peat dries, it oxidizes and evaporates, or is swept away by the wind, steadily robbing the Delta islands of about an inch in height each year. As they shrink in volume, the islands provide less and less of a buffer against the water pressure on the aging levees.

Subsidence explains why you can stand on a grassy field here, some 300 feet from the levees' edge, and look up to watch ships passing on the river. Some parts of Twitchell and other Delta islands are now more than 20 feet below sea level. Subsidence, and the growing pressure on the levees, also explain why there's more to the threat than the specter of water someday coursing over the levees. In some areas it's already seeping under them, says Deverel. That's forcing farmers to fortify old embankments while continually draining their land.

There's also a broader threat. Soggy peatlands can be powerful carbon sinks. All that changes when the peat dries out. As peat oxidizes, it releases stored CO₂. In the Delta, this translates to an area of about 150,000 acres of soil turned into "this weird little chimney in the middle of the state that is just pumping out carbon dioxide," says Campbell Ingram, executive director of the Delta Conservancy, a state agency that is collaborating with Deverel on the carbon-credits project.

Over more than 30 years of careful measurements, Deverel has found that each year, on average, each of those acres of dried-peat farmland emits roughly ten tons of CO₂, roughly equivalent to the annual emissions of 217,000 gas-powered cars.

Deverel, Ingram, and their colleagues see this as an opportunity.

Inundating the land, and allowing the ancient bulrushes and cattails to return-or potentially cultivating rice-would stop those emissions immediately, and even store carbon as new plants grow. Deverel and Ingram hope the process could start to reverse the subsidence by adding as much as two inches of soil a year as watery plants die and form new peat. "It's slow, yes-it could take 150 years to get back to sea-level," says Ingram. "But every added foot reduces the pressure on the levees."

Restoring Delta wetlands would have many other benefits as well. Healthy wetlands help filter freshwater, offer habitat for wildlife, and provide a buffer for flood control-all services increasingly in demand as climate change brings more devastating droughts and rising sea levels. In this way, the Delta project could shift the carbon credits paradigm, using the credits not only to reduce or "mitigate" greenhouse gas emissions but to help adapt to the inevitable results of climate change in coming years.

"This project is still in its early stages but we're very hopeful about what it implies for California's sustainability," says Michelle Passero, director of climate and nature-based solutions for The Nature Conservancy. The international non-profit, which owns an entire Delta island, has recently begun working with Deverel to greatly expand the scope of his plan, converting 4,000 acres from corn to rice and another 1,000 to restore wetlands habitat. Passero says they hope to generate carbon credits from the project within the next few years, providing income to pay for more restoration, and ideally creating a model for others to follow.

To do so, however, the Delta's defenders still need to overcome three daunting obstacles: the science, the expense, and the politics of wetlands conversion.

The Devil's in the data

In the first US attempt to farm carbon in US wetlands, the scientific calculations didn't add up.

In December 2013, Tierra Resources, a small environmental restoration firm based in New Orleans, announced that the American Carbon Registry had approved its "revolutionary new tool:" a "first of its kind" methodology to restore degraded wetlands in the Gulf of Mexico.

Seven years later, however, the company quietly canceled its pilot project in a Louisiana swamp. The problem was "high uncertainty with the data," wrote Tierra Resources CEO Sarah Mack in an email. The ACR requires periodic monitoring reports, meaning carbon farmers must continually prove they're doing what they initially promised.

Mack, who later consulted on the California Delta project, praised Deverel and colleagues for what she described as their pioneering work. "They showed it can be done," she said, "and that is going to encourage other scientists to follow them."

As Mack acknowledged, the Delta project has had some key advantages over her own effort. For one thing, after three decades of studying and measuring emissions from the land, Deverel has more scientific certainty. But more important is the problem of methane, a greenhouse gas that is about 25 times more powerful than CO2.

All wetlands emit methane, as anaerobic soil microbes digest growing plants. But Mack's wetlands in the Gulf of Mexico lacked the key ingredient of peat. In peat wetlands, inundating the land-and stopping up those weird little chimneys-has the potential to reduce so much CO2 that it would more than compensate for new methane emissions, according to Deverel.

Peat's promise is already inspiring some mega-projects in swamp forests, bogs, and fens, many thousands of miles away from the Delta. In Indonesia, the Katingan Metaya Project claims it is generating 7.5 million carbon credits per year from peat-rich forests, avoiding emissions equal to those of France. In Scotland, a fast-fashion billionaire is working on a project to farm carbon from peatlands on his extensive landholdings. Closer to home, in North Carolina, scientists have investigated the potential for a carbon farm on 10,000 acres of previously drained pocosins, wetland bogs with woody shrubs and sandy peat soil.

The clock is ticking. As peatlands increasingly dry out, those "weird little chimneys" are popping up all over the planet, potentially creating a dangerous feedback loop for climate change. That makes it all the more important that the Delta defenders find answers to the economic and political challenges of wetlands restoration.

Show me the money

Wetlands restoration is expensive, and the Delta carbon project is no exception. Over the past 12 years, California state agencies have spent nearly $17 million restoring and managing wetlands in the project area, according to Bryan Brock, an engineer for the California Department of Water Resources (DWR). That bill would have been much larger had the land not already been owned by DWR. Another $1.5 million was spent on research-related expenses, including 10 eddy covariance stations, which can cost $50,000 each, to measure gas flows and temperature changes over the wetlands.

Now, the biggest hurdle is making the project financially sustainable. For all its expense, the project has yet to produce any revenue. Carbon credits issued so far have gone to the project landowner, DWR, which can't sell the credits due to rules forbidding profits from publicly funded projects, as Brock explains.

To finance more wetlands restoration, the Delta team must do the political work of convincing thousands of farmers to convert at least some of their land from profitable crops to marshes or rice, and then keep them that way for a minimum of 40 years. Carbon prices have been rising, but at less than $10/ton for the voluntary market, are still far from enough to change a lot of minds.

"It's a bit ridiculous," is how Bruce Blodgett, executive director of the San Joaquin Farm Bureau Federation, characterizes the Delta carbon-farming proposal. "Are we supposed to buy our seeds with carbon credits?"

Blodgett worries the state will step in and force farmers to participate. He insists the Delta farmers are doing just fine dealing with subsidence by paying property taxes to fund work on the levees and, as long as the water keeps flowing, he doesn't want to change. "We have one area in the entire state of California that we know we can still be farming 150 years from now," he says, "and they want to plant tules there."

Yet Mother Nature increasingly has put her finger on the scales. As sea levels rise, that salty water seeping under the levees is already threatening crops, while farmers must pay more to keep draining their land. The increasing threats from climate change may also eventually move governments to act more aggressively, which could raise the price of carbon credits and provide another inducement for the farmers. "If we get to $100 a ton, that solves the problem," says Deverel.

In the meantime, he continues with his research and plans for the next phase of the project, on The Nature Conservancy land, continuing with the work that has now consumed more than half of his life. Progress so far has been small and slow, and maybe even a little nerve-wracking if you're the sort who tends to doom-scroll climate news.

But Deverel isn't one for doom-scrolling. "This is what I am called to do now," he says. "I don't need to worry about the entire stairway, just the next step."

Katherine Ellison wrote this article for Hothouse.