On a walk on an early spring day near his home in Harrisonburg, Virginia, Bronson Griscom talks about his team’s research findings in the manner of someone still waking from a profound dream. A tropical forest ecologist by training, TNC’s director of forest carbon science had long had a hunch that nature was a big part of the solution to climate change.

Griscom found a substantial body of published research assessing one or another specific way to use nature to fight climate change, whether it be restoring forests or farming in ways that more closely mimic nature. But, he says, “I was sifting through this [research], thinking, ‘Everybody’s looking at this from different angles, but nobody is really nailing the question: How does it all add up?’ That question hadn’t really been answered at a comprehensive level.”  

In 2014, Justin Adams, TNC’s global managing director for lands, asked the same question in a meeting. Griscom approached him afterward. “I was like, ‘We should totally do a little review paper on this,’” says Griscom. He remembers thinking, “It’ll be fun. No big deal. Just run some numbers.”

Adams urged him on—but counseled, as Griscom puts it, “This is a big deal, and we need to do this right.”

The quest to get the numbers right quickly assumed the feel of a scientific expedition. Natural systems are far messier than engineered ones. Calculating just how much carbon, say, an acre of dry steppe grassland can absorb, Griscom learned, “is way more complicated than calculating the climate benefits of a wind turbine.”

It took hiring a team of additional staff and two years of late hours and weekends—plus a dive into esoteric statistical techniques like Monte Carlo simulations, marginal abatement cost curves and the Delphi method for expert elicitation—to finally get an answer.

In 2017, Griscom and his team calculated in the Proceedings of the National Academy of Sciences that natural climate solutions can provide 37 percent of the carbon reductions needed to meet the goals of the Paris climate agreement—while also providing clean air, water and habitat for wildlife.

 “We tend to think of nature as a victim,” says Griscom. “But there’s been less attention to the phenomenal resilience and power of nature to heal. The ability of nature to solve problems just doesn’t get enough attention.”

The findings put a spotlight on actions along three broad lines (“The Green Path to a Stable Climate,” opposite). One embraces what many conservationists intuitively guessed: In most places, simply keeping nature intact helps absorb carbon from the atmosphere. Let tropical forests stand, leave coastal marshes undeveloped, and the vegetation in those places will keep on growing and storing carbon.

A second, intriguing strategy centers on managing working lands—such as farms, ranches and timberlands—with carbon in mind. The contribution in terms of carbon is smaller than that of restoration, but the strategy can be applied across large areas without taking lands out of production or harming local economies. The trick is finding the right combination of incentives to persuade agricultural producers and landowners to change how they manage the properties under their care.

The third strategy is to restore natural systems that have been damaged or destroyed, just as Benini and his colleagues hope to do in Brazil. Replanting forests offers enormous potential to capture carbon. But restoring other lands—grasslands, wetlands, coastal mangroves, even sea grasses—also significantly helps the climate picture.

In addition, the paper gets at an overlooked truth about the Paris climate agreement goals:  Eliminating the greenhouse gas emissions of fossil fuels is all-important, but cutting emissions alone won’t be enough to keep the temperature rise well below 2 degrees Celsius by 2030. Humankind needs to figure out how to absorb a lot of carbon that’s already in the atmosphere, and Griscom believes his findings offer a clear path for action.

“Nothing,” he says, “is as good as life at sucking carbon out of the atmosphere. There’s no machine we have that’s as good as life.”

One need go no further than upstate New York to find an example of how Griscom’s analysis can be turned into practice. Here, TNC is helping the Albany Water Board find a way to profitably dial up the carbon storage capacity on about 6,500 acres of city-owned forest whose only moneymaking potential in the past was as timber.

“Historically, the forest was used to fill fiscal holes,” says Troy Weldy, TNC’s senior conservation manager in New York. Albany is hardly alone in such practice, he notes. Many towns log their land holdings for cash to supplement their budgets.

After the U.S. decision to withdraw from the Paris Agreement in 2017, however, Albany Mayor Kathy Sheehan committed to taking on a part of the pledge that the U.S. government had just abandoned. At the same time, TNC was looking for partners to help it forge a new model for how owners of timberlands manage their forest holdings.

Under a new, carbon-focused plan developed by TNC, Albany’s forest began to look less like standing timber and a lot more like carbon credits. “We keep the trees in the ground for a longer period of time, so we’re growing bigger trees,” Weldy says. “And as the forest matures, it’s then sucking in and storing more carbon.” Using third-party certification and existing carbon markets, such as those in California and Quebec, Albany can earn credits for the extra carbon it is storing and sell those credits to buyers seeking to offset their own emissions.  

In addition to earning credits, the bigger trees also mean larger profits from the carefully planned timber sales that do happen. The bigger trees can be put to much better use as lumber for construction. “If you log a tree and it gets milled and put into a house, the carbon’s still stored,” Weldy says. “The life cycle of a house is going to be 100 to 200 years, and that carbon’s still locked up over that period.” By contrast, the harvesting of smaller trees is usually for firewood, which immediately returns stored carbon to the atmosphere when burned.

It’s shaping up to be a switch that makes financial sense. When TNC figured the potential revenues for the water authority, says Weldy, “our conservative estimate was half a million dollars in 10 years by allowing the trees to grow longer.” Now, with a more detailed forest inventory in hand and Albany’s decision to include more land, Weldy believes that the new management scheme may actually deliver closer to
$1 million to the city’s coffers.

Looking at conservation efforts through a climate lens can push projects in new directions, depending on the economic drivers that affect land-use decisions. 

In places with extensive forests, keeping trees standing becomes enormously important—and that has put renewed attention on empowering indigenous communities to manage their traditional lands. In British Columbia, for example, the Great Bear Rainforest holds one of the world’s largest stores of carbon. Here TNC worked with 27 First Nations to help them gain rights to manage much of their traditional territories and train a new generation of leaders and entrepreneurs in sustainable forest management. These indigenous communities finalized an agreement with the Canadian and provincial governments in 2016, after more than a decade of planning and negotiation. The agreement places 9 million acres of rainforest off-limits to logging and puts millions more acres under strict forest management guidelines.

In Indonesia, where forestry has played a large part in economic growth over the past five decades, TNC’s Griscom helped develop techniques to minimize the amount of carbon emitted during legal logging operations. Simple changes, most notably ensuring that only commercially valuable trees are cut, can reduce emissions by as much as half. This year, the Indonesian government adopted the system for use throughout the entire country, and TNC is adapting it for use in Mexico, Peru, Gabon and Suriname.

Farmlands and ranchlands offer a lot of potential, too. “This does not require fundamentally rethinking what is being produced on working lands,” says Griscom. “But we do need to rethink our practices on those lands.”

For example, practices such as planting cover crops between growing seasons increase the amount of carbon stored in soils. By far the biggest low-cost gains in agriculture could come simply from using fertilizers correctly. Plants can take up only a certain amount of nitrogen, so when farmers apply too much nitrogen-based fertilizer, it needlessly costs them time and money. Worse, the fertilizer reacts with the air and forms nitrous oxides, which are a potent greenhouse gas.  

Likewise, pragmatic changes to the management of pastures—for example, letting grass recuperate between episodes of grazing—can help. In Kenya, TNC has been working with the Northern Rangeland Trust for a decade to create community-supported norms around how communal grasslands are managed. By giving pastures more time to recover, cattle owners build up the amount of grass on the ground—an outcome that is good for the herd, good for the pastures and measurably good for storing more carbon.

The carbon equation has given many conservationists a renewed zeal for habitat protection. Coastal wetlands, for example—mangroves, saltmarshes and sea grasses—store carbon in soils, where the water seals it in. Drain or develop these areas, and “that’s thousands of years of carbon being released into the atmosphere,” says Emily Landis, TNC’s coastal wetlands strategy lead.

By contrast, keeping the same habitat intact makes climate sense. Mangrove forests can store up to four times more carbon per hectare than terrestrial forests. Mangroves also help shield coastal communities from storms.

In that respect, protecting mangroves—just like using less fertilizer on farm fields—improves the lives of people.  

In Brazil, Rubens Benini has seen that dynamic. Just four years after beginning on-the-ground restoration work in the Mantiqueira Mountains, Benini began to see evidence of large mammals like pumas returning to the reforested areas.

“I have spent almost an entire lifetime working on this,” he says. “When we see animals that we imagined had completely disappeared from this region come back, it’s a very nice feeling. But when you get inside of a restored forest and see the animals and the clean water and the rivers—the whole picture—the feeling is completely amazing.”