A new climate modeling study suggests that large-scale reforestation could be less effective as a carbon removal strategy if the climate is highly sensitive to carbon dioxide (CO₂) emissions.
The research, conducted between 2023 and 2025 by the Finnish Meteorological Institute in collaboration with GEOMAR Helmholtz Centre for Ocean Research Kiel and NASA’s Jet Propulsion Laboratory, examined how different carbon removal methods perform under varying levels of climate sensitivity.
The study focused on two approaches: large-scale reforestation and ocean alkalinity enhancement, modeled under a scenario limiting global warming to below 2°C.
Results show that the effectiveness of reforestation depends on how strongly global temperatures respond to cumulative CO₂ emissions. Under higher climate sensitivity, the mitigation potential of reforestation declines.
By 2100, reforestation could be around 11% less effective under high climate sensitivity scenarios, with the reduction increasing to 33% by 2300. The researchers modeled reforestation as a scenario in which global adoption of a vegan diet by 2050 frees up land currently used for livestock, allowing natural vegetation to expand.
Despite the decline in efficiency under certain conditions, reforestation remains a significant mitigation option. The study estimates it could remove nearly 250 gigatons of CO₂ between 2050 and 2100, equivalent to roughly six years of current global emissions.
In contrast, ocean alkalinity enhancement – modeled through the addition of calcium hydroxide to ocean surfaces – was found to remove a consistent amount of CO₂ regardless of climate sensitivity. The process increases the ocean’s capacity to absorb CO₂ from the atmosphere.
The findings highlight the importance of considering uncertainties in both carbon removal methods and climate sensitivity when developing mitigation strategies.
The researchers said the results are particularly relevant for policymakers, as reforestation may be less effective in scenarios where climate change impacts are more severe.
The study emphasizes that carbon dioxide removal approaches should complement rather than replace emissions reductions in efforts to meet the Paris Agreement target of limiting global temperature rise to well below 2°C.
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