The trillion-tree myth: Why reforestation can’t save us

When I think about tree planting, it reminds me of my early days at Carbonsink. At that time, many companies built their entire sustainability strategy around trees. We planted forests for everything: the “employees’ forest,” forests for events, for travel, for products. Every month, new private and public initiatives came out with the same promise: to plant more and more trees. We started with millions and ended up talking about billions. I never did that in the early days at Carbonsink; we focused instead on community-based projects such as household energy efficiency, access to clean energy, and renewable energy programs.

I have always been a big fan of trees. I truly believe in their power; they intercept pollutants and contribute to stormwater management, they give us oxygen, shade, beauty, biodiversity, and a sense of peace that connects us with nature. Trees are essential for our well-being and for the health of our planet. Sometimes, when I ride my bike through Milan on a crazy hot summer day and enter a tree-lined avenue, I can immediately feel the difference; the air becomes cooler, fresher, calmer. Just one block can change everything. That is the quiet, real power of trees.

But as much as I admire them, I have also learned trees can play a crucial role in mitigating and adapting to the climate crisis, but they cannot solve it on their own. The idea that we can simply plant our way out of the climate crisis is a beautiful story and a deeply misleading one. Behind the glossy campaigns and political pledges lies a hard physical reality: the planet simply doesn’t have enough suitable land, water, or time.

Over the past decade, I’ve met countless people dreaming of large-scale reforestation projects with the ambition to restore millions of hectares. Most of these projects fail, for reasons that are always the same: lack of capital, unclear land rights, weak implementation capacity, and the systematic overestimation of tree growth rates and carbon uptake. Many projects assume perfect conditions, fast growth, low mortality, stable climate, and use optimistic carbon models that translate directly into inflated credit numbers. Droughts, pests, fires, and management gaps often reduce sequestration well below projections. As a result, the carbon accounting of reforestation is frequently exaggerated, creating a false sense of progress and a large gap between credits issued and carbon actually stored. This often translates into a financing gap and a lack of long-term capital to sustain the projects once the initial enthusiasm fades.

I’ve always been skeptical about reforestation at scale because, aside from commercial plantations, the idea of financing reforestation purely through carbon credits is simply not sustainable in the long run.

A new study published in Science (Wang et al., 2025) provides the most advanced and realistic assessment of the global potential for forestation. Unlike earlier optimistic estimates (Griscom 2017, Bastin 2019), the authors integrated ecological, political, and socio-economic limits, excluding areas where planting trees would cause more harm than good.

After removing regions with biodiversity risks, water scarcity, or negative albedo effects, the results are sobering: 389 million hectares of land remain suitable for forestation (about 4 million km²), capable of absorbing around 146 billion tons of CO₂ by 2050. When limited to areas already included in national commitments, the potential drops to about 46 billion tons of CO₂, less than 1.5% of projected cumulative emissions through 2050.

Even more telling, 95% of that potential lies in low- and middle-income countries, where the technical and financial capacity to deliver large-scale forestation is limited.

Reforestation does matter for biodiversity, soil, and livelihoods, but the idea that it may solve the effects of global warming is a dangerous illusion. The math doesn’t work: there isn’t enough land that doesn’t compete with food or people, trees take decades to grow while the carbon clock ticks fast, and planting trees where they don’t belong can disrupt ecosystems, water cycles, and even increase local temperatures by reducing albedo.

In other words, the dream of a “global forest” is not just unfeasible, it’s often counterproductive.

Even in the best scenario, forestation could absorb around 1.5 billion tons of CO₂ per year, less than one-twentieth of today’s fossil-fuel emissions. This isn’t a systemic solution; it’s a marginal contribution. The problem isn’t the tree; it’s the myth that we can plant enough of them to offset the physics of burning carbon.

Reforestation has real climatic value, it restores ecosystems, cools landscapes, and supports biodiversity , but it cannot replace deep decarbonization. As Wang and colleagues conclude, even under optimistic conditions, tree planting will make only a small dent in global emissions.

The real transformation lies elsewhere: decarbonizing energy, redesigning industries, and rethinking consumption.

This article is also published on Substack. illuminem Voices is a democratic space presenting the thoughts and opinions of leading Sustainability & Energy writers, their opinions do not necessarily represent those of illuminem.

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