KETI BANDAR, Pakistan — Wildlife ranger Mohammad Jamali boats through mangrove forests of the Indus River Delta, the terminus of a curly waterway that begins thousands of miles upstream in the Himalayas. Birds flutter in and out. Insects dart around mangrove roots that poke like fingers out of the mud. It looks ancient, but this part of the forest is only 5 years old.

"We planted this," says Jamali, 28-years-old. We — rangers of the wildlife department of the government of the southern Pakistani province of Sindh, and locals of nearby fishing communities.

This forest in southern Pakistan is part of one of the world's largest mangrove restoration projects, covering much of the vast delta, an area nearly the size of Rhode Island. These trees, which exist in slivers between sea and land, are powerhouses of sucking up the carbon dioxide that is dangerously heating up the planet.

"They do this very big job per hectare," says Catherine Lovelock, an expert on coastal ecology. Mangroves capture, or sequester, carbon dioxide "through their roots and into the soil, as well as above ground," she says.

This mangrove reforestation effort alone in the Indus Delta is expected to absorb an estimated 142 million tons of carbon dioxide over the next sixty years. It's a test case for restoration, and planting mangroves at this scale might help the fight to curb planetary warming.

Speaking over gusty winds, Jamali, the wildlife ranger, says reforestation began here two decades ago after a cyclone swept through and killed dozens of people. The area was hit hard, because the mangrove forests that once fringed this area had died away over the decades after successive Pakistani governments built dams upstream that deprived the delta of fresh water. The mangroves were a buffer between the sea and local communities, muting the impact of storm surges during cyclones and heavy storms.

According to Afia Salam, an environmental campaigner, it was a former Sindh wildlife ranger, Tahir Qureshi, who pioneered planting mangrove species that don't need so much fresh water, because there's so little of it now in the Indus River Delta.

Qureshi died in 2020 after a lifetime of advocacy for mangroves, and on behalf of the impoverished fishing communities that rely on them to attract aquatic life. Salam recalls fisherfolk called him "baba," or father, "because they respected what he was doing," she says, "how he was benefiting the communities."

Qureshi oversaw the forestation of some 30,000 hectares of mangrove forest over the decades. But planting efforts were supercharged after a Pakistani company, Delta Blue Carbon, partnered with the provincial government to restore more than a hundred thousand hectares of degraded forests, and to plant an area more than double that with new mangroves.

Building out a mangrove forest, sapling by sapling

Jamali, the wildlife ranger, jumps out of the boat to show how they are expanding mangrove forests. From a mangrove tree, he snaps off a thing that looks like a spear. It's a propagule, basically, an already germinated seed that drops from the mother tree and lodges into the muddy, wet soil below.

Workers harvest the propagules and raise them in nurseries on the forest outskirts. When they're hardy enough, the workers plant them elsewhere. That scale of reforestation takes years, and has so far cost millions – far more than the provincial government was willing, or even able, to spend on its own.

The company Delta Blue Carbon has chiefly funded these efforts, spending years preparing this project, making agreements with local communities and the government. The company undertook this project so it could sell the mangrove's carbon dioxide removal service as credits to polluting companies.

Delta Blue Carbon representatives declined to respond to a detailed list of questions.

The way carbon credits work is if a company emits a ton of planet-heating carbon dioxide, it can pay another company to do some activity that absorbs a ton of carbon dioxide. Carbon dioxide can be absorbed and stored many ways, including by planting forests, restoring wetlands and in this part of Pakistan, planting mangroves.

Delta Blue's carbon credit program works by planting mangroves that suck up and store carbon dioxide and then it sells credits for that activity. This is big business in a world where companies are trying to show they are compensating for the carbon dioxide they are emitting, also called becoming "carbon neutral".

But is it "carbon colonialism"?

In Pakistan, some environmentalists say without carbon credits, this massive reforestation project wouldn't have happened. They say the government was incentivized to support it. Instead of having to find the budget to do this, the government is being paid proceeds from carbon credit sales.

So far, Delta Blue Carbon has sold two batches of credits, most recently in June. It's made the provincial government around $40 million so far, according to local media outlet Arab News. It's big money in a poor country.

"It is paying money. It is generating revenue," says ecologist Rafiul Haq who consulted on the mangrove project. Haq says without that revenue stream, the government would be under pressure to let developers in, for shrimp farms or for seaside homes.

Haq says there's another benefit: auditors must evaluate the company's progress before they can sell more carbon credits, which means the mangrove forests are nurtured and protected, and the company has to show local communities are benefiting. "This is a blessing for us," Haq says. "We have to present ourselves as the good boy," he laughs.

To other environmentalists, the mangrove project is "carbon colonialism."

"I don't begrudge anyone, especially in areas like these, for taking money for large scale restoration projects like this," says Polly Hemming, director of the climate and energy program of the progressive think tank, the Australia Institute. But she says, "it's just another form of carbon colonialism. Like, we'll give you some money to restore your land," and then, sell "your credits to a polluter so they can continue emitting."

Underscoring that argument, Hemming pointed to one of the key purchasers of these carbon credits is one of the world's largest fossil fuel trading companies, Trafigura. It is also one of the world's largest traders of carbon credits. Through a spokesperson, the company declined to comment for this story.

In Keti Bandar, in a fishing hut near the jetty, 23-year-old Gul Zamir shakes freshly caught blue crabs into freezer boxes for market. He says crab, shrimp and fish have been returning in greater numbers as the mangroves have expanded. He calls them "nurseries" for sea life, and magnets that bring back catches.

He says a few years ago his family could only eat one meal a day – rice and lentils, or fish that he caught. Now he says, they're eating three meals a day – "beef, mutton, chicken," Zamir crows, and pats his belly. That's where he measures the difference.