Carbon Credits Versus the “Big Gulp”

Carbon Credits Versus the "Big Gulp" thumbnail

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 is a Davis-based hydrologist who refers to this threat by the name “The Big Gulp” as a breach that would draw in river water and tens or billions of gallons. 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 such disaster to occur.

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. The farmland was submerged four feet by the water. Houseboats and cruisers of thirty-foot length crashed against the embankments. Many people were seriously hurt as hundreds fled the rising waters. 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 is now aiming to save the Delta by inundating it before the Pacific can. He also wants to pay for it using carbon credits.

“Carbon-farming” in the wetlands

Deverel, 70, has spent three decades trying to head off the Big Gulp. His chance is climate change. 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. New plants that grow in these restored wetlands will absorb carbon dioxide (CO2), the most potent greenhouse gas, out of the atmosphere each year. They will store it in strata of accumulating soil that will support the dikes against collapse.

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. This makes it the first and only wetland project to generate carbon credits in the US. Steve Crooks, a Sausalito-based scientist in wetlands and global expert on “carbon-farming” from coastal areas, said that this is the first and only such project.

The Delta project is another one of very few such efforts in the world, but its promise is immense.

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. Environmental scientists see restoring wetlands as a huge source of carbon credits, as countries and corporations increase their commitments to reduce greenhouse gas emissions. The earth’s wetlands could be restored to their former glory, and may even have more environmental benefits than carbon projects in forestry.

But managing these landscapes can be more difficult and expensive than simply flooding fields or replanting tree. Deverel believes that the Delta project has shown a way forward. The key to success is peat, a rich, brown and crumbly soil.

The promise of peat

A few thousand years after the last Ice Age ended, the Delta was covered in a freshwater, marshy inland sea. Over the millennia, layers made up of moss and mud, along with vegetation, have accumulated to create peat. Peatlands can store large amounts of carbon if they are given the right conditions. Marshes “sequester” CO2 by photosynthesis, which allows them to store it as they grow. The carbon remains in the plants until they die or decompose under water. Peat can be used to grow crops once it is drained. This was discovered by the Gold Rush settlers. “Swamplanders” were Chinese farmers who hired Chinese laborers to construct the levees and drain marshes. They then planted rows upon rows of corn and alfalfa. Later, they added other crops such as wine grapes, walnut trees, almond trees, cotton, sugarbeets, and blueberries.

It would take more than a century before scientists realized that farmers were creating their own ruin.

The problem is called “subsidence”, a gentle term for a dangerous situation. Peat can oxidize and evaporate, or be swept away by wind. Each year, the Delta islands are robbed of approximately one inch of their height. The islands shrink in volume and provide less protection against the rising 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 increasing pressure on the levees are also reasons why there is more to the threat that the specter water one day coursing over them. Deverel says that water is already seeping beneath them in some areas. Farmers are forced to reinforce old embankments and drain their land constantly because of this.

There’s also a bigger threat. Soggy peatlands can be powerful carbon sinks. This all changes when the peat dries. Peat oxidizes and 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 and Ingram see this opportunity.

Allowing the old bulrushes, cattails, and to return–or possibly cultivating rice-–would stop these emissions immediately and store carbon as new plants are grown. Deverel, Ingram and others hope that the process will reverse subsidence by adding up to two inches of soil per year as watery plants cease to exist and form new peat. “It’s slow, yes–it could take 150 years to get back to sea-level,” says Ingram. “But every foot decreases the pressure on the .”


Restoring Delta wetlands would also have many other benefits. Healthy wetlands are essential for freshwater filtering, wildlife habitat, and flood control. These services are increasingly in demand due to climate change’s increasing severity and rising sea level. The Delta project could change the paradigm in carbon credits, using the credits to not only reduce or “mitigate”, greenhouse gas emissions, but also to adapt to the inevitable effects of climate change in the coming years.

” Although the project is still in its infancy, we are optimistic about what it means for California’s sustainability,” Michelle Passero (director of climate-based solutions and climate change for The Nature Conservancy) says. 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 said they expect to generate carbon credits from this project in the next few years. This will provide income to pay for further restoration and, ideally, create a model for other people to follow.

To do this, however, the Delta’s defenders must overcome three formidable obstacles: science, expense, and politics of wetlands conversion.

The Devil is in the


In the first US attempt at farming carbon in US wetlands the scientific calculations were not correct.

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 cancelled its pilot project in a Louisiana swamp. Tierra Resources CEO Sarah Mack wrote in an email that the problem was “high uncertainties with the data”. Carbon farmers must submit periodic monitoring reports to the ACR, which means they have to prove that they are delivering on their initial promises.

Mack later worked with the California Delta project as a consultant and praised Deverel’s pioneering work. She said that Deverel and her colleagues “showed it could be done” and that this will encourage other scientists to follow their lead .”


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

All wetlands emit methane because anaerobic soil microbes consume growing plants. Mack’s wetlands in Gulf of Mexico, however, lacked the essential ingredient of peat. According to Deverel, peat wetlands can be inundated with water and stopped by tiny chimneys. This could reduce CO2 levels so much that it would more than offset new methane emissions.

Peat is already inspiring mega-projects in swamp forests and bogs, thousands of miles from the Delta. The Katingan Metaya Project in Indonesia claims it generates 7.5 million carbon credits annually from peat-rich forests and avoids emissions comparable to France. A fast-fashion billionaire in Scotland is currently working on a project that will farm carbon from peatlands on large 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. Peatlands are becoming increasingly dry, and these “weird little chimneys”, which could potentially create a dangerous feedback loop for climate changes, are appearing all over the globe. It is crucial that Delta defenders address the economic and political issues associated with wetlands restoration.

Show Me the Money

Wetlands restoration can be expensive. 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). If the land had not been owned by DWR, that bill would have been even higher. 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 obstacle is making the project financially viable. Despite all the expense, the project has not yet produced any revenue. The carbon credits have been issued to DWR, the project landowner. DWR cannot sell the credits because of rules prohibiting profits from publicly funded projects. 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 is a bit absurd,” is how Bruce Blodgett (executive director of San Joaquin Farm Bureau Federation) describes the Delta carbon-farming plan. “Are we supposed buy our seeds with carbon credit ?

Blodgett is concerned that the state will intervene and force farmers to take part. He claims that the Delta farmers are doing a great job of subsidence management by paying property taxes to finance work on the levees. He doesn’t want to change as long as the water is flowing. “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.”

But Mother Nature is increasingly weighing the scales. Sea levels rising means that salt water seeping beneath the levees is already threatening crops and farmers have to pay more to continue draining their land. The growing threat of climate change could also prompt governments to take more aggressive measures, which could increase the price for carbon credits and offer farmers another incentive. “If we get to $100 a ton, that solves the problem,” says Deverel.

In the meantime, he continues his research and plans to complete the next phase on The Nature Conservancy land. This is continuing with the work which has taken up more than half his life. If you are the type who likes to scroll through climate news and doom-scroll, progress has been slow and insignificant.

But Deverel doesn’t believe in doom-scrolling. He says, “This is what my calling is now.” “I don’t have to worry about the whole stairway, just the next .”

This story originally appeared in Hothouse and is part of Covering Climate Now, a global journalism collaboration strengthening coverage of the climate story.


    Katherine Ellison is a Pulitzer Prize-winning journalist.

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