A forest the size of Mexico could store twice as much carbon as was thought. That makes its conservation even more valuable

Editor’s Note: Call to Earth is a CNN editorial series committed to reporting on the environmental challenges facing our planet, together with the solutions. Rolex’s Perpetual Planet Initiative has partnered with CNN to drive awareness and education around key sustainability issues and to inspire positive action.

It’s been called the world’s biggest mammal migration; from October to December, up to 10 million straw-colored fruit bats travel from across Africa and gather over a swamp forest in Kasanka National Park, at the heart of Zambia’s Miombo woodland.

They leave in January, many returning to other locations within the vast dry Miombo forest surrounding the park — which provides these bats with year-round habitat and a bountiful supply of fruit

Stretching from the northern tips of Tanzania, through to coastal Angola in the west, and all the way down to southern Mozambique, the Miombo covers 1.9 million square kilometers (734,000 square miles): an area about the size of Mexico.

It’s thought to provide livelihoods and essential resources for over 300 million people, as well as sustaining much of Africa’s most iconic megafauna, including some of the continent’s largest remaining elephant populations.

Despite its importance, the Miombo saw a decline in forest cover of almost a third between 1980 and 2020. However, recent research shed light on its ability to store carbon, which could mean that restoring the woodland has more economic value than cutting it down.

Double the carbon

A first-of-its-kind study published in July 2024 found that the Miombo may be locking up more than twice as much aboveground carbon as was previously thought. This difference equates to an additional 3.7 billion metric tons of carbon stored across the whole forest — more than that emitted into the atmosphere by China in 2023.

Professor Mathias Disney, of University College London, who co-authored the paper, explains that the oversimplified relationship between trunk diameter and tree mass (of which carbon makes up a fixed proportion) used in prior estimates, “kind of underpins everything we know about carbon and forests worldwide.”

Instead, this new study predicted the aboveground biomass in the Miombo using a much more advanced method: lidar (light detection and ranging). Much as sonar relies on sound pulses, and radar on radio pulses, lidar builds up a 3D-map by firing thousands of laser pulses per second at an object and recording the reflected signals.

The team deployed the imaging technique from the ground, from drones and from helicopters, over a 500-square-kilometer region of the forest in Mozambique. They then used their data to build the most accurate 3D-representation of the woodland to date and extrapolated to estimate the amount of carbon locked up across the whole Miombo.

Accurately gauging this figure is hugely important. Article 6 of the 2015 Paris Agreement on climate change says that countries gain “carbon credits” based on performance, relative to their emissions targets. Countries that over-perform can sell excess carbon credits to companies that want to offset their emissions, or countries that under-perform, allowing these to also meet their targets.

As far as the Miombo is concerned, although “nothing has actually changed on the ground… if you double the amount of carbon that’s stored across these woodlands… you’ve essentially doubled their dollar value overnight,” says Disney. This means doubling the financial incentive for southern African nations to protect and restore the Miombo, but also doubling the financial cost of cutting it down.

Restoration Alliance

The Miombo Restoration Alliance, a collaboration between 11 southern African nations, conservation organizations, and Trafigura — a global commodities trading group — was formed in September 2024. Trafigura is funding $500 million for the scheme to finance forest restoration projects, which would allow for the sale of carbon removal credits under Article 6.

“In the carbon world, everything flows from policy, everything flows from regulation,” says Hannah Hauman, global head of carbon trading at Trafigura. With governments committing to funding and enforcing stricter environmental regulation, she says that the Alliance has the potential to become “the largest nature-based removals initiative on the planet.”

The Miombo Alliance’s first pilot scheme was announced in November 2024 at the COP29 climate conference in Azerbaijan. It is focused on promoting sustainable land use among local communities in Mozambique’s Gorongosa District, with an aim to research the regional potential for carbon offsets through this.

However, carbon offsets under the Paris Agreement are controversial.

Rachel Rose Jackson, director of climate research and policy at Corporate Accountability — a non-profit watchdog that challenges transnational corporations on ethical practices — says that Article 6 often serves as “a pollution allowance rather than an actual emissions reduction.” Effectively, the countries and corporations that pollute most heavily can continue do so, by paying people elsewhere to offset their emissions for them, she says.

Jackson points to a 2023 study of 2,000 offset projects which found that only 12% of existing credits actually constituted any real emissions reductions. The carbon trading market is “full of loopholes, it’s riddled with weaknesses, and on the whole, it’s absolutely not working,” she says.

Though Jackson makes it clear that she is not criticizing the Miombo Restoration Alliance specifically, she says that governments must shift away from “dangerous distractions like offsets and carbon markets” and instead focus on keeping fossil fuels in the ground.

“Much more than carbon”

For Disney, “forests are much more than carbon.” While keeping carbon locked up in the woodland is incredibly important from a climate perspective, it “says nothing about biodiversity,” nor about “food, resources, shelter, aesthetics, health benefits to people,” he explains.

Edwin Tambara, director of Global Leadership at the African Wildlife Foundation, says that compared to rainforests such as the Amazon and the Congo Basin, dry forests like the Miombo are systematically understudied, underappreciated and undervalued.

Reflecting on his own childhood, growing up surrounded by the Miombo in Zimbabwe, Tambara says “we relied on the ecosystem in terms of every aspect of our lives.”

His community depended on the forest for termite-resistant construction materials, food supplies, even toothache-curing medicines, he explains. A 2016 study valued such provisions to rural livelihoods across the Miombo — and the geographically overlapping Mopane woodlands — at $9 billion per year.

“Africans owning conservation is important and Africans leading on conservation is important,” says Tambara, praising the newly formed intergovernmental program. However, he insists that conserving the Miombo in the long term must serve to protect the local people and biodiversity that relies on it, as well as the carbon that it locks up.

As an example, he describes a 2016 project in which the African Wildlife Foundation introduced a drought-resistant sugarcane variety to smallholder farmers in Tanzania’s Kilombero District, an important region for sugar production. Farmers receiving the new variety saw a 70% increase in sugarcane yields, which significantly reduced the need to deforest the surrounding Miombo in order to expand their agricultural plots.

He reminisces about the “traditional rules” when he was young, dictating which plants could be gathered and which must be preserved — rules that he later realized reflected a deep-rooted local understanding of both the scarcity and societal importance of different species.

Tambara adds: “Communities who live day in, day out in these woodlands… have a lot of indigenous knowledge that we need to tap into in terms of how best to conserve (the woodlands).”

For more CNN news and newsletters create an account at CNN.com