New study shows high climate sensitivity may reduce the effectiveness of large-scale reforestation

Researchers studied two carbon dioxide removal methods: large-scale reforestation and ocean alkalinity enhancement. The methods were analyzed under a scenario in which global warming is limited to below 2 °C.

The study shows that the effectiveness of carbon dioxide (CO₂) removal can depend on how sensitive the climate is to cumulative CO₂ emissions, but the effect varies between methods. Climate sensitivity to cumulative CO₂ emissions refers to how much the temperature increases per total amount of CO₂ emissions emitted into the atmosphere.

Reforestation and ocean alkalinity enhancement were analyzed

Reforestation was designed as an idealized scenario in which the global population adopts a vegan diet in 2050. As a result, natural vegetation can expand to areas previously used as pasture and cropland for livestock production.

The mitigation potential of reforestation decreases as climate sensitivity to cumulative CO₂ emissions increases. Reforestation achieves the greatest CO₂ removal if the climate is less sensitive to CO₂ emissions than current estimates suggest. Conversely, its effectiveness declines as climate sensitivity increases. Specifically, by 2100 reforestation would be about 11% less effective under very high climate sensitivity, and by 2300 this reduction would increase to 33%. Despite uncertainty and this coupling with climate sensitivity, reforestation through global vegan diet was a strong mitigation option, sequestering almost 250 Gt of CO₂ between 2050 and 2100 (equivalent to about six years of present-day CO₂ emissions).

Ocean alkalinity enhancement was implemented by simulating the addition of calcium hydroxide (slaked lime) to the surface of the ice-free ocean from 2050 onwards. In this scenario, the lime reacts with CO₂ and removes it from the ocean surface, which in turn increases the absorption of CO₂ from the atmosphere to the ocean.

Carbon removal through ocean alkalinity enhancement does not depend on climate sensitivity to cumulative CO₂ emissions. According to the simulations, this method removes a constant amount of CO₂ regardless of how much the planet warms in the future.

Results support climate policy planning

These findings are important for both the scientific community and policymakers. The coupled uncertainties in carbon dioxide removal and climate sensitivity should be considered when designing robust climate change mitigation strategies.

The study highlights that reforestation could become less efficient in a future where climate sensitivity is high – precisely when effective mitigation would be needed the most.

Research on carbon dioxide removal is critical for developing effective climate mitigation strategies. Such methods are needed alongside strong emission reductions to meet the Paris Agreement target of limiting global temperature increase to well below 2 °C.

The research was conducted in 2023–2025 at the Finnish Meteorological Institute in collaboration with GEOMAR Helmholtz Centre for Ocean Research Kiel and the Jet Propulsion Laboratory at the California Institute of Technology.

Further information:

Doctoral researcher Carla Maria Di Natale, Finnish Meteorological Institute, carla.di.natale@fmi.fi

The scientific article is openly available in Environmental Research Letters.

Reference: Carla M. Di Natale et al 2026 Environ. Res. Lett. 21 024033. https://doi.org/10.1088/1748-9326/ae20a5