PLANT CITY, Fla. — The preserve stretches for thousands of acres, its teeming wetlands alternating with forests where ultra-straight lumber pines grow side-by-side with their lusher, native cousins.

At Hillsborough County’s Lower Green Swamp, officials are working to restore the land from cow pastures and a former pine plantation back to its natural state. The trees in the preserve also offer up something else: They’re a source of more than $1 million in county revenue.

About 5,200 acres of the preserve is enrolled in a “carbon bank” program that cashes in on how much carbon the trees are estimated to capture.

It’s part of a global billion-dollar industry, where each ton of carbon that trees remove from the atmosphere can be bought by companies wanting to offset their pollution. Each ton is represented by one carbon “credit,” which the buyers then subtract from their own emissions ledgers. The companies may buy the credits for mandatory reasons, like complying with government emissions ceilings, or voluntarily to improve their public image on environmental issues.

Hillsborough officials said the local program is a win-win for taxpayers and the environment. A small number of carbon credit registries, including the American Carbon Registry, set rules for the projects and issue credits if they meet those standards.

“All the money that is generated out of this carbon bank goes straight back to restoration in the Lower Green Swamp preserve,” said Ross Dickerson, environmental lands manager for the county.

But while it sounds like a straightforward tradeoff between emissions and the trees that capture them, carbon credits have come under scientific scrutiny. The accounting is frequently abused or inaccurate, experts say, and these projects can do more harm than good in the fight against climate change.

The evidence has been “pretty unequivocal” in terms of the impact of carbon credit programs like the one in use at the Lower Green Swamp, said Danny Cullenward, a senior fellow with the Kleinman Center for Energy Policy at the University of Pennsylvania and the vice chairperson of California’s Independent Emissions Market Advisory Committee.

“The atmosphere is being screwed over by these deals,” he said.

How carbon credits work

Hillsborough County worked with an outside group that used complex calculations to determine how much carbon is captured by the trees in the preserve.

That group, an Oregon nonprofit called The Climate Trust, estimated that the trees will store more than 300,000 metric tons of carbon dioxide-equivalent over a 20-year period. That means companies or other entities can buy about 300,000 credits generated by the Lower Green Swamp over time.

In an interview with the Tampa Bay Times, Julius Pasay, executive director of the Climate Trust, declined to disclose who has bought Hillsborough County’s credits or how much they paid, saying the buyer (or buyers) wished to remain anonymous. But the global average price of a credit in 2022 was $7.37, according to a report by Ecosystem Marketplace, an environmental finance group. Pasay said high demand for the type of credit produced by the Lower Green Swamp has pushed those prices into the double digits.

All of Climate Trust’s credits are sold to buyers in the “voluntary market,” Pasay said, such as companies trying to meet their own internal emissions goals. Big corporations across the world have purchased credits in the voluntary market, including Disney, Gucci, Salesforce and Shell, according to the Guardian.

Hillsborough County’s project remains fairly small-scale for now. It has generated just under $1.3 million so far, with a couple hundred thousand more expected in coming years.

But the Lower Green Swamp could be the beginning of a larger movement in Florida of using government land to generate carbon revenue. County officials believe it’s the first carbon bank on government land in the state. Dickerson said he’s fielded calls from other local governments, including Pasco County, asking how they can follow Hillsborough’s lead.

Hillsborough also plans to enroll thousands more acres to expand its use of carbon credits. That push would begin next year with planting millions of trees that would eventually become eligible for restoration credits, Dickerson said.

Do carbon credits help or hurt?

Scientists have said the world must transition away from fossil fuels to avoid the worst of climate change. Carbon credits, some scientists say, could slow that trajectory by allowing companies to claim green bona fides without meaningfully changing their operations.

Plus, journalists and researchers have uncovered problems with the quality of carbon credits, including companies claiming to save forests from development that were never under threat to begin with, because they were already on preserved land.

In order for carbon credits to work, they must be adding additional climate benefits than would have existed without intervention, such as preserving trees that were about to get razed for a shopping mall. Otherwise, carbon credits are simply a get-out-of-jail-free card for polluting companies to pay money to look like they’re taking action, some experts say, while nothing changes about emissions.

So what would have happened in Hillsborough County without the carbon bank program?

The county would have managed the land differently, Dickerson said, more quickly cutting down non-native trees so they could be replaced with native species. “Because of the carbon project, we stopped cutting down these trees until our replacement (group of trees is) mature enough that it offsets what would have been lost if we cut down these trees.”

Pasay said the Lower Green Swamp is enrolled in a carbon credit program designed for situations like this, where the owner could make more money by turning the trees into timber compared to maintaining them.

Still, there’s a disconnect between what the county says would have been done with the land absent a carbon program, and what was written in the documents submitted to the American Carbon Registry.

Those documents, prepared by the Climate Trust with assistance from the county, state that the county could have clear cut the land before converting the property “to slash pine plantations” for timber — the exact thing that the county has been working for more than a decade to reverse by planting native species.

When asked about this wording, the county said that that’s because that scenario could happen based on common practices on nearby land. It doesn’t have to be what the county would do with 100% certainty absent a carbon program, under the rules.

“By agreeing to protect (the trees) through carbon banking, we added an additional layer of protection for the next 40 years,” Dickerson, from the county, wrote in an email. “This was important to us because you never know what could happen in the future,” such as if the price of lumber increases and adds pressure for the county to harvest its trees.

Barbara Haya, a research fellow at the University of California Berkeley who’s been studying carbon offset quality for two decades, said that the problems go beyond any one project to the structure of carbon credit programs.

“The rules are lax and the proof is only that you could do it, and not that you likely would have done it,” she said. “That’s how we have so many false credits on the market today.”

Scientists have identified another problem with carbon credits: While the programs’ land protections are temporary, the carbon dioxide emissions they are supposed to offset stay in the atmosphere for centuries. That means that when the carbon bank agreements expire, trees can be cut down whose existence helped a company justify additional pollution.

Despite this imperfection, carbon credits shouldn’t be discounted, Pasay said, because they’re a valuable action that people can take right now.

“People aren’t going to stop driving cars today,” he said. “It’s to get us to the point where we can be a more fossil fuel-free society.”

Numbers vs. nature

On a recent spring afternoon at the Lower Green Swamp, a bobwhite quail darted by the windshield of Dickerson’s truck in a flash of wings and spots.

“God, that’s so cool!” he said. He’d never seen that species here before, but the quail are coming back as the land is restored.

Pasay said beyond the columns of carbon stored versus emitted, projects like the Lower Green Swamp help preserve nature in ways that transcend numbers.

“Protecting water quality, wildlife habitat corridors ... that’s what inspires me,” he said.

Cullenward, the climate researcher, agrees that conserving land is valuable. He just wishes companies wouldn’t use that to argue that a certain number of trees is equivalent to the pollution they emit.

“I am sympathetic to the mission of governments and landowners trying to do right” by preserving land, he said. “I am deeply suspicious of how this industry has created this marketing regime under which is there are often fact patterns where they say they’re going to do one thing (with the land) and they’re doing another. The whole systems is designed to take good intentions and turn them into green-washing.”

The way Dickerson sees it, carbon bank programs reveal something fundamental about our warming world.

“We have something on these lands that’s becoming more and more valuable, which is trees — which is kind of sad,” he said. “We bought this land, and now the land value, when it comes to carbon and those trees that are here, has increased. And people want to pay you for that.”

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