GLOBAL – October 2, 2025 – New research published in the journal Science warns that global pledges to plant billions of trees as a cornerstone of carbon reduction may be based on wildly optimistic land and sequestration estimates. The study found that the amount of land previously deemed suitable for forestation an area about the size of India shrank by as much as two-thirds when vital environmental and social constraints were factored in.
The research co-authored by Josep “Pep” Canadell, executive director of the Global Carbon Project, determined that once adverse impacts on biodiversity, food security, and water resources are accounted for the potential for existing tree-planting pledges to store an estimated 40 gigatons of carbon by 2050 drops significantly to just 12.5 gigatons.
Policy Constraints Deflate Carbon Promises
The study used new modeling tools that compared global carbon sequestration rates based on existing pledges with the realistic limits of those commitments. Researchers also recognized that permanently deforested lands, such as those used for agriculture or ranching are highly unlikely to return to forest.
Canadell stressed that policymakers have “sold reforestation as a kind of easier path [to fighting climate change], and it’s not easy at all,” citing the immense complexity that arises when managing landscapes where people live and need food.
The findings severely undercut the notion that massive forestation projects alone can offset continued high fossil fuel emissions. For example, the study found that despite accounting for half of the 230 million hectares pledged globally for forestation by 2030, only 4% of the land in Africa is actually suitable for such massive tree-planting without harming critical savannas and grasslands.
Prioritizing Existing Forests Over New Planting
The study top-line message urges policymakers to be more pragmatic, prioritize and accelerate forestation initiatives where they are truly viable, and focus on replanting with native tree species rather than low-biodiversity monoculture plantations.
However, other experts argue that the focus should shift entirely. William Moomaw, an environmental policy professor emeritus at Tufts University, contends that greater protection of existing biodiverse forests is the more urgent and effective climate action priority. Moomaw noted that current forests already remove an amount of atmospheric \text{CO}_2 equal to almost 30% of annual fossil fuel emissions, and their conservation offers a faster, more reliable mitigation strategy than new planting.
In short, while the 12.5 gigatons of carbon storage potential is important representing new forests roughly the size of South Africa the research forces a more realistic reckoning with the limitations of reforestation as a primary climate solution.