Why Planting Billions of Trees Alone Won’t Solve Climate Change: Unpacking the Math Behind Global Efforts

Josep “Pep” Canadell, director of the Global Carbon Project, urges caution when countries promise to plant billions of trees as a quick fix for climate change. He highlights that reforestation isn’t as simple as it seems. “We’ve marketed it as an easier path, but it’s actually really complex,” he told Mongabay. Managing landscapes, especially where people live, adds layers of difficulties.

A new study in the journal Science, co-authored by Canadell, reveals that the land available for new trees—an area about the size of India—drops significantly when we factor in concerns like biodiversity, food security, and water resources. Researchers mapped how carbon in the soil changes after tree planting. They found that while existing pledges suggest we could capture an extra 40 gigatons of carbon by 2050, the number shrinks to just 12.5 gigatons when we consider real-world challenges.

That’s not insignificant. If these new forests are well-maintained, they could cover an area similar to South Africa, helping tackle climate change. However, this amount is far below the initial 40 gigatons deemed necessary to slow down the alarming pace of climate change.

The Importance of Planting Trees Wisely

Over the last five years, many global assessments have touted reforestation potential, often with inflated figures and a lack of ecological nuance. Canadell points out that areas like Africa, home to many large mammals, are being eyed for tree planting, even though only 4% of the continent is truly viable for it. Half of the 230 million hectares pledged for forestation globally by 2030 are supposed to be in Africa.

In contrast, a separate study from The Nature Conservancy highlights that the success of tree-planting initiatives greatly depends on how and where we plant trees. Even with ideal conditions, their impact is limited.

Katherine Sinacore, a restoration ecologist at James Madison University, reviewed the Science study and praised its modeling. It corrects previous overestimations of available land for reforestation. She believes action is key: “It’s not hard to plant a tree, but keeping it alive and thriving is a challenge.”

Prioritizing Natural Forests

Experts argue that focusing on natural forests is critical. William Moomaw, an environmental policy professor at Tufts University, suggests that protecting existing biodiverse forests should take priority over new reforestation efforts. These forests already absorb significant amounts of CO2—around 30% of annual fossil fuel emissions.

As climate change accelerates, plant-based strategies can offer a part of the solution, but they should not overshadow the work needed to cut down fossil fuel use. Moomaw emphasizes, “Restoring existing forests is urgent. New plantings will take decades to produce significant environmental benefits.”

Conclusion

The conversation around tree planting is evolving. While planting trees can be a valuable tool in combating climate change, it is crucial to approach it thoughtfully. We must recognize the limitations of existing land for reforestation and place greater emphasis on protecting natural forests to meet our climate goals effectively.

For more in-depth insights on climate action and sustainability, check out the original articles from Mongabay.

Citations:

1. Wang, Y. et al. (2025). Land availability and policy commitments limit global climate mitigation forestation. Science.
2. Fesenmyer, K. A. et al. (2025). Addressing critiques refines global estimates of reforestation potential for climate change mitigation. Nature Communications.

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